|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | DESCRIPTION | SUDOERS FILE FORMAT | SUDOERS OPTIONS | GROUP PROVIDER PLUGINS | EVENT LOGGING | I/O LOGGING | FILES | EXAMPLES | SECURITY NOTES | DEBUGGING | SEE ALSO | AUTHORS | CAVEATS | BUGS | SUPPORT | DISCLAIMER | COLOPHON |
|
|
|
SUDOERS(5) File Formats Manual SUDOERS(5)
sudoers — default sudo security policy plugin
The sudoers policy plugin determines a user's sudo privileges.
It is the default sudo policy plugin. The policy is driven by
the /etc/sudoers file or, optionally, in LDAP. The policy format
is described in detail in the “SUDOERS FILE FORMAT” section. For
information on storing sudoers policy information in LDAP, see
sudoers.ldap(5).
Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which plugins to
load. If no sudo.conf(5) file is present, or if it contains no
Plugin lines, sudoers will be used for auditing, policy decisions
and I/O logging. To explicitly configure sudo.conf(5) to use the
sudoers plugin, the following configuration can be used.
Plugin sudoers_audit sudoers.so
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible to specify optional
arguments to the sudoers plugin in the sudo.conf(5) file. Plugin
arguments, if any, should be listed after the path to the plugin
(i.e., after sudoers.so). The arguments are only effective for
the plugin that opens (and parses) the sudoers file.
For sudo version 1.9.1 and higher, this is the sudoers_audit
plugin. For older versions, it is the sudoers_policy plugin.
Multiple arguments may be specified, separated by white space.
For example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
error_recovery=bool
The error_recovery argument can be used to control whether
sudoers should attempt to recover from syntax errors in the
sudoers file. If set to true (the default), sudoers will
try to recover from a syntax error by discarding the
portion of the line that contains the error until the end
of the line. A value of false will disable error recovery.
Prior to version 1.9.3, no error recovery was performed.
ignore_perms=bool
The ignore_perms argument can be used to disable security
checks when loading the sudoers file. If enabled, the
sudoers file will be loaded regardless of the owner or file
mode. This argument is intended to be used for testing
purposes and should not be enabled on production systems.
ldap_conf=pathname
The ldap_conf argument can be used to override the default
path to the ldap.conf file.
ldap_secret=pathname
The ldap_secret argument can be used to override the
default path to the ldap.secret file.
sudoers_file=pathname
The sudoers_file argument can be used to override the
default path to the sudoers file.
sudoers_uid=user-ID
The sudoers_uid argument can be used to override the
default owner of the sudoers file. It should be specified
as a numeric user-ID.
sudoers_gid=group-ID
The sudoers_gid argument can be used to override the
default group of the sudoers file. It must be specified as
a numeric group-ID (not a group name).
sudoers_mode=mode
The sudoers_mode argument can be used to override the
default file mode for the sudoers file. It should be
specified as an octal value.
For more information on configuring sudo.conf(5), refer to its
manual.
User Authentication
The sudoers security policy requires that most users authenticate
themselves before they can use sudo. A password is not required
if the invoking user is root, if the target user is the same as
the invoking user, or if the policy has disabled authentication
for the user or command. Unlike su(1), when sudoers requires
authentication, it validates the invoking user's credentials, not
the target user's (or root's) credentials. This can be changed
via the rootpw, targetpw and runaspw flags, described later.
If a user who is not listed in the policy tries to run a command
via sudo, mail is sent to the proper authorities. The address
used for such mail is configurable via the mailto Defaults entry
(described later) and defaults to root.
No mail will be sent if an unauthorized user tries to run sudo
with the -l or -v option unless there is an authentication error
and either the mail_always or mail_badpass flags are enabled.
This allows users to determine for themselves whether or not they
are allowed to use sudo. By default, all attempts to run sudo
(successful or not) are logged, regardless of whether or not mail
is sent.
If sudo is run by root and the SUDO_USER environment variable is
set, the sudoers policy will use this value to determine who the
actual user is. This can be used by a user to log commands
through sudo even when a root shell has been invoked. It also
allows the -e option to remain useful even when invoked via a
sudo-run script or program. Note, however, that the sudoers file
lookup is still done for root, not the user specified by
SUDO_USER.
sudoers uses per-user time stamp files for credential caching.
Once a user has been authenticated, a record is written
containing the user-ID that was used to authenticate, the
terminal session ID, the start time of the session leader (or
parent process) and a time stamp (using a monotonic clock if one
is available). The user may then use sudo without a password for
a short period of time (5 minutes unless overridden by the
timestamp_timeout option). By default, sudoers uses a separate
record for each terminal, which means that a user's login
sessions are authenticated separately. The timestamp_type option
can be used to select the type of time stamp record sudoers will
use.
The tsdump utility, included with the sudo source distribution,
can be used to display the contents of a time stamp file. See
sudoers_timestamp(5) for details of the time stamp file format.
Logging
By default, sudoers logs both successful and unsuccessful
attempts (as well as errors). The log_allowed and log_denied
flags can be used to control this behavior. Messages can be
logged to syslog(3), a log file, or both. The default is to log
to syslog(3) but this is configurable via the syslog and logfile
settings. See “EVENT LOGGING” for a description of the log file
format.
sudoers is also capable of running a command in a pseudo-terminal
and logging input and/or output. The standard input, standard
output, and standard error can be logged even when not associated
with a terminal. For more information about I/O logging, see the
“I/O LOGGING” section.
Starting with version 1.9, the log_servers setting may be used to
send event and I/O log data to a remote server running
sudo_logsrvd or another service that implements the protocol
described by sudo_logsrv.proto(5).
Command environment
Since environment variables can influence program behavior,
sudoers provides a means to restrict which variables from the
user's environment are inherited by the command to be run. There
are two distinct ways sudoers can deal with environment
variables.
By default, the env_reset flag is enabled. This causes commands
to be executed with a new, minimal environment. On AIX (and
Linux systems without PAM), the environment is initialized with
the contents of the /etc/environment file. The HOME, MAIL,
SHELL, LOGNAME and USER environment variables are initialized
based on the target user and the SUDO_* variables are set based
on the invoking user. Additional variables, such as DISPLAY,
PATH and TERM, are preserved from the invoking user's environment
if permitted by the env_check, or env_keep options. A few
environment variables are treated specially. If the PATH and
TERM variables are not preserved from the user's environment,
they will be set to default values. The LOGNAME and USER are
handled as a single entity. If one of them is preserved (or
removed) from the user's environment, the other will be as well.
If LOGNAME and USER are to be preserved but only one of them is
present in the user's environment, the other will be set to the
same value. This avoids an inconsistent environment where one of
the variables describing the user name is set to the invoking
user and one is set to the target user. Environment variables
with a value beginning with ‘()’ are removed unless both the name
and value parts are matched by env_keep or env_check, as they may
be interpreted as functions by the bash shell. Prior to version
1.8.11, such variables were always removed.
If, however, the env_reset flag is disabled, any variables not
explicitly denied by the env_check and env_delete options are
allowed and their values are inherited from the invoking process.
Prior to version 1.8.21, environment variables with a value
beginning with ‘()’ were always removed. Beginning with version
1.8.21, a pattern in env_delete is used to match bash shell
functions instead. Since it is not possible to block all
potentially dangerous environment variables, use of the default
env_reset behavior is encouraged.
Environment variables specified by env_check, env_delete, or
env_keep may include one or more ‘*’ characters which will match
zero or more characters. No other wildcard characters are
supported.
By default, environment variables are matched by name. However,
if the pattern includes an equal sign (‘=’), both the variables
name and value must match. For example, a bash shell function
could be matched as follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the ‘=()*’ suffix, this would not match, as bash shell
functions are not preserved by default.
The complete list of environment variables that are preserved or
removed, as modified by global Defaults parameters in sudoers, is
displayed when sudo is run by root with the -V option. The list
of environment variables to remove varies based on the operating
system sudo is running on.
Other settings may influence the command environment:
• sudoers options such as always_set_home, secure_path,
set_logname, set_home, and setenv.
• Command tags, such as SETENV and NOSETENV. Note that SETENV
is implied if the command matched is ALL.
• sudo options, such as -E and -i.
On systems that support PAM where the pam_env module is enabled
for sudo, variables in the PAM environment may be merged in to
the environment. If a variable in the PAM environment is already
present in the user's environment, the value will only be
overridden if the variable was not preserved by sudoers. When
env_reset is enabled, variables preserved from the invoking
user's environment by the env_keep list take precedence over
those in the PAM environment. When env_reset is disabled,
variables present the invoking user's environment take precedence
over those in the PAM environment unless they match a pattern in
the env_delete list.
The dynamic linker on most operating systems will remove
variables that can control dynamic linking from the environment
of set-user-ID executables, including sudo. Depending on the
operating system this may include _RLD*, DYLD_*, LD_*, LDR_*,
LIBPATH, SHLIB_PATH, and others. These type of variables are
removed from the environment before sudo even begins execution
and, as such, it is not possible for sudo to preserve them.
As a special case, if the -i option (initial login) is specified,
sudoers will initialize the environment regardless of the value
of env_reset. The DISPLAY, PATH and TERM variables remain
unchanged; HOME, MAIL, SHELL, USER, and LOGNAME are set based on
the target user. On AIX (and Linux systems without PAM), the
contents of /etc/environment are also included. All other
environment variables are removed unless permitted by env_keep or
env_check, described above.
Finally, the restricted_env_file and env_file files are applied,
if present. The variables in restricted_env_file are applied
first and are subject to the same restrictions as the invoking
user's environment, as detailed above. The variables in env_file
are applied last and are not subject to these restrictions. In
both cases, variables present in the files will only be set to
their specified values if they would not conflict with an
existing environment variable.
The sudoers file is composed of two types of entries: aliases
(basically variables) and user specifications (which specify who
may run what).
When multiple entries match for a user, they are applied in
order. Where there are multiple matches, the last match is used
(which is not necessarily the most specific match).
The sudoers file grammar will be described below in Extended
Backus-Naur Form (EBNF). Don't despair if you are unfamiliar
with EBNF; it is fairly simple, and the definitions below are
annotated.
Resource limits
By default, sudoers uses the operating system's native method of
setting resource limits for the target user. On Linux systems,
resource limits are usually set by the pam_limits.so PAM module.
On some BSD systems, the /etc/login.conf file specifies resource
limits for the user. On AIX systems, resource limits are
configured in the /etc/security/limits file. If there is no
system mechanism to set per-user resource limits, the command
will run with the same limits as the invoking user. The one
exception to this is the core dump file size, which is set by
sudoers to 0 by default. Disabling core dumps by default makes
it possible to avoid potential security problems where the core
file is treated as trusted input.
Resource limits may also be set in the sudoers file itself, in
which case they override those set by the system. See the
rlimit_as, rlimit_core, rlimit_cpu, rlimit_data, rlimit_fsize,
rlimit_locks, rlimit_memlock, rlimit_nofile, rlimit_nproc,
rlimit_rss, rlimit_stack options described below. Resource
limits in sudoers may be specified in one of the following
formats:
“value”
Both the soft and hard resource limits are set to the
same value. The special value “infinity” can be used to
indicate that the value is unlimited.
“soft,hard”
Two comma-separated values. The soft limit is set to the
first value and the hard limit is set to the second.
Both values must either be enclosed in a set of double
quotes, or the comma must be escaped with a backslash
(‘\’). The special value “infinity” may be used in place
of either value.
“default”
The default resource limit for the user will be used.
This may be a user-specific value (see above) or the
value of the resource limit when sudo was invoked for
systems that don't support per-user limits.
“user” The invoking user's resource limits will be preserved
when running the command.
For example, to restore the historic core dump file size
behavior, a line like the following may be used.
Defaults rlimit_core=default
Resource limits in sudoers are only supported by version 1.8.7 or
higher.
Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a
language. Each EBNF definition is made up of production rules.
For example:
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a
grammar for the language. EBNF also contains the following
operators, which many readers will recognize from regular
expressions. Do not, however, confuse them with “wildcard”
characters, which have different meanings.
? Means that the preceding symbol (or group of symbols) is
optional. That is, it may appear once or not at all.
* Means that the preceding symbol (or group of symbols) may
appear zero or more times.
+ Means that the preceding symbol (or group of symbols) may
appear one or more times.
Parentheses may be used to group symbols together. For clarity,
we will use single quotes ('') to designate what is a verbatim
character string (as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias,
Host_Alias and Cmnd_Alias. Beginning with sudo 1.9.0, Cmd_Alias
may be used in place of Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias,
or Cmnd_Alias. A NAME is a string of uppercase letters, numbers,
and underscore characters (‘_’). A NAME must start with an
uppercase letter. It is possible to put several alias
definitions of the same type on a single line, joined by a colon
(‘:’). For example:
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is
possible to use the same name for aliases of different types, but
this is not recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user-IDs
(prefixed with ‘#’), system group names and IDs (prefixed with
‘%’ and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-
Unix group names and IDs (prefixed with ‘%:’ and ‘%:#’
respectively), and User_Aliases. Each list item may be prefixed
with zero or more ‘!’ operators. An odd number of ‘!’ operators
negate the value of the item; an even number just cancel each
other out. User netgroups are matched using the user and domain
members only; the host member is not used when matching.
A user name, user-ID, group, group-ID, netgroup, nonunix_group or
nonunix_gid may be enclosed in double quotes to avoid the need
for escaping special characters. Alternately, special characters
may be specified in escaped hex mode, e.g., \x20 for space. When
using double quotes, any prefix characters must be included
inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the
underlying group provider plugin. For instance, the QAS AD
plugin supports the following formats:
• Group in the same domain: "%:Group Name"
• Group in any domain: "%:Group [email protected]"
• Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See “GROUP PROVIDER PLUGINS” for more information.
Quotes around group names are optional. Unquoted strings must
use a backslash (‘\’) to escape spaces and special characters.
See “Other special characters and reserved words” for a list of
characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias |
'!'* ALL
A Runas_List is similar to a User_List except that instead of
User_Aliases it can contain Runas_Aliases. User names and groups
are matched as strings. In other words, two users (groups) with
the same user (group) ID are considered to be distinct. If you
wish to match all user names with the same user-ID (e.g., root
and toor), you can use a user-ID instead of a name (#0 in the
example given). The user-ID or group-ID specified in a
Runas_Member need not be listed in the password or group
database.
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias |
'!'* ALL
A Host_List is made up of one or more host names, IP addresses,
network numbers, netgroups (prefixed with ‘+’), and other
aliases. Again, the value of an item may be negated with the ‘!’
operator. Host netgroups are matched using the host (both
qualified and unqualified) and domain members only; the user
member is not used when matching. If you specify a network
number without a netmask, sudo will query each of the local
host's network interfaces and, if the network number corresponds
to one of the hosts's network interfaces, will use the netmask of
that interface. The netmask may be specified either in standard
IP address notation (e.g., 255.255.255.0 or
ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g.,
24 or 64). A host name may include shell-style wildcards (see
the “Wildcards” section below), but unless the hostname command
on your machine returns the fully qualified host name, you'll
need to use the fqdn flag for wildcards to be useful. sudo only
inspects actual network interfaces; this means that IP address
127.0.0.1 (localhost) will never match. Also, the host name
“localhost” will only match if that is the actual host name,
which is usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[A-Za-z0-9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= regex |
file name
command ::= command name |
command name args |
command name regex |
command name '""' |
ALL
Edit_Spec ::= "sudoedit" file name+ |
"sudoedit" regex |
"sudoedit"
List_Spec ::= "list"
Cmnd ::= Digest_List? '!'* command |
'!'* directory |
'!'* Edit_Spec |
'!'* List_Spec |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more commands, directories, or
aliases. A command is a fully qualified file name, which may
include shell-style wildcards (see the “Wildcards” section
below), or a regular expression that starts with ‘^’ and ends
with ‘$’ (see the “Regular expressions” section below). A
directory is a fully qualified path name ending in a ‘/’. When
you specify a directory in a Cmnd_List, the user will be able to
run any file within that directory (but not in any sub-
directories therein). If no command line arguments are
specified, the user may run the command with any arguments they
choose. Command line arguments can include wildcards or be a
regular expression that starts with ‘^’ and ends with ‘$’. If
the command line arguments consist of ‘""’, the command may only
be run with no arguments.
If a Cmnd has associated command line arguments, the arguments in
the Cmnd must match those given by the user on the command line.
If the arguments in a Cmnd begin with the ‘^’ character, they
will be interpreted as a regular expression and matched
accordingly. Otherwise, shell-style wildcards are used when
matching. Unless a regular expression is specified, the
following characters must be escaped with a ‘\’ if they are used
in command arguments: ‘,’, ‘:’, ‘=’, ‘\’. To prevent arguments
in a Cmnd that begin with a ‘^’ character from being interpreted
as a regular expression, the ‘^’ must be escaped with a ‘\’.
There are two commands built into sudo itself: “list” and
“sudoedit”. Unlike other commands, these two must be specified
in the sudoers file without a leading path.
The “list” built-in can be used to permit a user to list another
user's privileges with sudo's -U option. For example, “sudo -l
-U otheruser”. A user with the “list” privilege is able to list
another user's privileges even if they don't have permission to
run commands as that user. By default, only root or a user with
the ability to run any command as either root or the specified
user on the current host may use the -U option. No command line
arguments may be specified with the “list” built-in.
The “sudoedit” built-in is used to permit a user to run sudo with
the -e option (or as sudoedit). It may take command line
arguments just as a normal command does. Unlike other commands,
“sudoedit” is built into sudo itself and must be specified in the
sudoers file without a leading path. If a leading path is
present, for example /usr/bin/sudoedit, the path name will be
silently converted to “sudoedit”. A fully-qualified path for
sudoedit is treated as an error by visudo.
A command may be preceded by a Digest_List, a comma-separated
list of one or more Digest_Spec entries. If a Digest_List is
present, the command will only match successfully if it can be
verified using one of the SHA-2 digests in the list. Starting
with version 1.9.0, the ALL reserved word can be used in
conjunction with a Digest_List. The following digest formats are
supported: sha224, sha256, sha384, and sha512. The string may be
specified in either hex or base64 format (base64 is more
compact). There are several utilities capable of generating
SHA-2 digests in hex format such as openssl, shasum, sha224sum,
sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself
(directly or via a sudo command), it may be possible for the user
to replace the command after the digest check has been performed
but before the command is executed. A similar race condition
exists on systems that lack the fexecve(2) system call when the
directory in which the command is located is writable by the
user. See the description of the fdexec setting for more
information on how sudo executes commands that have an associated
digest.
Command digests are only supported by version 1.8.7 or higher.
Defaults
Certain configuration options may be changed from their default
values at run-time via one or more Default_Entry lines. These
may affect all users on any host (‘Defaults’), all users on a
specific host (‘Defaults@host’), a specific user
(‘Defaults:user’), a specific command (‘Defaults!cmnd’), or
commands being run as a specific user (‘Defaults>runasuser’).
White space is not permitted between ‘Defaults’ and the ‘@’, ‘:’,
‘!’, or ‘>’ characters. While a comma-separated list may be used
in place of a single value after the ‘@’, ‘:’, ‘!’, or ‘>’
character, using an alias instead of a list is often improve
readability. Per-command entries may not include command line
arguments. If you need to specify arguments, define a Cmnd_Alias
and reference that instead.
Default_Type ::= 'Defaults' |
'Defaults@' Host_List |
'Defaults:' User_List |
'Defaults!' Cmnd_List |
'Defaults>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists.
Flags are implicitly boolean and can be turned off via the ‘!’
operator. Some integer, string and list parameters may also be
used in a boolean context to disable them. Values may be
enclosed in double quotes ("") when they contain multiple words.
Special characters may be escaped with a backslash (‘\’).
To include a literal backslash character in a command line
argument you must escape the backslash twice. For example, to
match ‘\n’ as part of a command line argument, you must use
‘\\\\n’ in the sudoers file. This is due to there being two
levels of escaping, one in the sudoers parser itself and another
when command line arguments are matched by the fnmatch(3) or
regexec(3) function.
Lists have two additional assignment operators, ‘+=’ and ‘-=’.
These operators are used to add to and delete from a list
respectively. It is not an error to use the ‘-=’ operator to
remove an element that does not exist in a list.
Defaults entries are parsed in the following order: global, host,
user, and runas Defaults first, then command defaults. If there
are multiple Defaults settings of the same type, the last
matching setting is used. The following Defaults settings are
parsed before all others since they may affect subsequent
entries: fqdn, group_plugin, runas_default, sudoers_locale.
See “SUDOERS OPTIONS” for a list of supported Defaults
parameters.
User specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* (Tag_Spec ':')* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec)
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC' | 'NOEXEC' | 'FOLLOW' | 'NOFOLLOW' |
'LOG_INPUT' | 'NOLOG_INPUT' | 'LOG_OUTPUT' |
'NOLOG_OUTPUT' | 'MAIL' | 'NOMAIL' | 'INTERCEPT' |
'NOINTERCEPT' | 'PASSWD' | 'NOPASSWD' | 'SETENV' |
'NOSETENV')
A user specification determines which commands a user may run
(and as what user) on specified hosts. By default, commands are
run as root (unless runas_default has been set to a different
value) but this can also be changed on a per-command basis.
The basic structure of a user specification is “who where =
(as_whom) what”. Let's break that down into its constituent
parts:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command
may be run as. A fully-specified Runas_Spec consists of two
Runas_Lists (as defined above) separated by a colon (‘:’) and
enclosed in a set of parentheses. The first Runas_List indicates
which users the command may be run as via the -u option. The
second defines a list of groups that may be specified via the -g
option (in addition to any of the target user's groups). If both
Runas_Lists are specified, the command may be run with any
combination of users and groups listed in their respective
Runas_Lists. If only the first is specified, the command may be
run as any user in the list and, optionally, with any group the
target user belongs to. If the first Runas_List is empty but the
second is specified, the command may be run as the invoking user
with the group set to any listed in the Runas_List. If both
Runas_Lists are empty, the command may only be run as the
invoking user and the group, if specified, must be one that the
invoking user is a member of. If no Runas_Spec is specified, the
command may only be run as the runas_default user (root by
default) and the group, if specified, must be one that the
runas_default user is a member of.
A Runas_Spec sets the default for the commands that follow it.
What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the
host boulder—but only as operator. For example:
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an
entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but
/bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the
user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
While the group portion of the Runas_Spec permits the user to run
as command with that group, it does not force the user to do so.
If no group is specified on the command line, the command will
run with the group listed in the target user's password database
entry. The following would all be permitted by the sudoers entry
above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a
modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
In this example only the group will be set, the command still
runs as user tcm. For example:
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in
which case the user may select any combination of users and
groups via the -u and -g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin,
optionally setting the group to operator or system.
Option_Spec
A Cmnd may have zero or more options associated with it. Options
may consist of start and/or end dates and command timeouts. Once
an option is set for a Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit that option unless it is overridden by
another option. Option names are reserved words in sudoers.
This means that none of the valid option names (see below) can be
used when declaring an alias.
Date_Spec
sudoers rules can be specified with a start and end date via the
NOTBEFORE and NOTAFTER settings. The time stamp must be
specified in “Generalized Time” as defined by RFC 4517. The
format is effectively ‘yyyymmddHHMMSSZ’ where the minutes and
seconds are optional. The ‘Z’ suffix indicates that the time
stamp is in Coordinated Universal Time (UTC). It is also
possible to specify a timezone offset from UTC in hours and
minutes instead of a ‘Z’. For example, ‘-0500’ would correspond
to Eastern Standard time in the US. As an extension, if no ‘Z’
or timezone offset is specified, local time will be used.
The following are all valid time stamps:
20170214083000Z
2017021408Z
20160315220000-0500
20151201235900
Timeout_Spec
A command may have a timeout associated with it. If the timeout
expires before the command has exited, the command will be
terminated. The timeout may be specified in combinations of
days, hours, minutes, and seconds with a single-letter case-
insensitive suffix that indicates the unit of time. For example,
a timeout of 7 days, 8 hours, 30 minutes, and 10 seconds would be
written as ‘7d8h30m10s’. If a number is specified without a
unit, seconds are assumed. Any of the days, minutes, hours, or
seconds may be omitted. The order must be from largest to
smallest unit and a unit may not be specified more than once.
The following are all valid timeout values: ‘7d8h30m10s’, ‘14d’,
‘8h30m’, ‘600s’, ‘3600’. The following are invalid timeout
values: ‘12m2w1d’, ‘30s10m4h’, ‘1d2d3h’.
This setting is only supported by version 1.8.20 or higher.
Chdir_Spec
The working directory that the command will be run in can be
specified using the CWD setting. The directory must be a fully-
qualified path name beginning with a ‘/’ or ‘~’ character, or the
special value “*”. A value of “*” indicates that the user may
specify the working directory by running sudo with the -D option.
By default, commands are run from the invoking user's current
working directory, unless the -i option is given. Path names of
the form ~user/path/name are interpreted as being relative to the
named user's home directory. If the user name is omitted, the
path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Chroot_Spec
The root directory that the command will be run in can be
specified using the CHROOT setting. The directory must be a
fully-qualified path name beginning with a ‘/’ or ‘~’ character,
or the special value “*”. A value of “*” indicates that the user
may specify the root directory by running sudo with the -R
option. This setting can be used to run the command in a
chroot(2) “sandbox” similar to the chroot(8) utility. Path names
of the form ~user/path/name are interpreted as being relative to
the named user's home directory. If the user name is omitted,
the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Tag_Spec
A command may have zero or more tags associated with it. The
following tag values are supported: EXEC, NOEXEC, FOLLOW,
NOFOLLOW, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL,
NOMAIL, INTERCEPT, NOINTERCEPT, PASSWD, NOPASSWD, SETENV, and
NOSETENV. Once a tag is set on a Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit the tag unless it is overridden by the
opposite tag (in other words, PASSWD overrides NOPASSWD and
NOEXEC overrides EXEC).
EXEC and NOEXEC
If sudo has been compiled with noexec support and the
underlying operating system supports it, the NOEXEC tag can be
used to prevent a dynamically-linked executable from running
further commands itself.
In the following example, user aaron may run /usr/bin/more and
/usr/bin/vi on the host shanty, but shell escapes will be
disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the “Preventing shell escapes” section below for more
details on how NOEXEC works and whether or not it will work on
your system.
FOLLOW and NOFOLLOW
Starting with version 1.8.15, sudoedit will not open a file
that is a symbolic link unless the sudoedit_follow flag is
enabled. The FOLLOW and NOFOLLOW tags override the value of
sudoedit_follow and can be used to permit (or deny) the editing
of symbolic links on a per-command basis. These tags are only
effective for the sudoedit command and are ignored for all
other commands.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input flag on a per-
command basis. For more information, see “I/O LOGGING”.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output flag on a per-
command basis. For more information, see “I/O LOGGING”.
MAIL and NOMAIL
These tags provide fine-grained control over whether mail will
be sent when a user runs a command by overriding the value of
the mail_all_cmnds flag on a per-command basis. They have no
effect when sudo is run with the -l or -v options. A NOMAIL
tag will also override the mail_always and mail_no_perms
options. For more information, see the descriptions of
mail_all_cmnds, mail_always, and mail_no_perms in the “SUDOERS
OPTIONS” section below.
PASSWD and NOPASSWD
By default, sudo requires that a user authenticate before
running a command. This behavior can be modified via the
NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a
default for the commands that follow it in the Cmnd_Spec_List.
Conversely, the PASSWD tag can be used to reverse things. For
example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and
/usr/bin/lprm as root on the machine “rushmore” without
authenticating himself. If we only want ray to be able to run
/bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who
are in the group specified by the exempt_group setting.
By default, if the NOPASSWD tag is applied to any of a user's
entries for the current host, the user will be able to run
‘sudo -l’ without a password. Additionally, a user may only
run ‘sudo -v’ without a password if all of the user's entries
for the current host have the NOPASSWD tag. This behavior may
be overridden via the verifypw and listpw options.
SETENV and NOSETENV
These tags override the value of the setenv flag on a per-
command basis. If SETENV has been set for a command, the user
may disable the env_reset flag from the command line via the -E
option. Additionally, environment variables set on the command
line are not subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users should be
allowed to set variables in this manner. If the command
matched is ALL, the SETENV tag is implied for that command;
this default may be overridden by use of the NOSETENV tag.
INTERCEPT and NOINTERCEPT
If sudo has been compiled with intercept support and the
underlying operating system supports it, the INTERCEPT tag can
be used to cause programs spawned by a command to be validated
against sudoers and logged just like they would be if run
through sudo directly. This is useful in conjunction with
commands that allow shell escapes such as editors, shells, and
paginators. There is additional overhead due to the policy
check that may add latency when running commands such as shell
scripts that execute a large number of sub-commands. For
interactive commands, such as a shell or editor, the overhead
is not usually noticeable.
In the following example, user chuck may run any command on the
machine “research” in intercept mode.
chuck research = INTERCEPT: ALL
See the “Preventing shell escapes” section below for more
details on how INTERCEPT works and whether or not it will work
on your system.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters)
to be used in host names, path names, and command line arguments
in the sudoers file. Wildcard matching is done via the glob(3)
and fnmatch(3) functions as specified by IEEE Std 1003.1
(“POSIX.1”).
* Matches any set of zero or more characters (including
white space).
? Matches any single character (including white space).
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character ‘x’, evaluates to ‘x’. This is used to
escape special characters such as: ‘*’, ‘?’, ‘[’, and
‘]’.
These are not regular expressions. Unlike a regular expression
there is no way to match one or more characters within a range.
Character classes may be used if your system's glob(3) and
fnmatch(3) functions support them. However, because the ‘:’
character has special meaning in sudoers, it must be escaped.
For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
A forward slash (‘/’) will not be matched by wildcards used in
the file name portion of the command. This is to make a path
like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does
get matched by wildcards since command line arguments may contain
arbitrary strings and not just path names.
Wildcards in command line arguments should be used with care.
Wildcards can match any character, including white space. In
most cases, it is safer to use a regular expression to match
command line arguments. For more information, see “Wildcards in
command arguments” below.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string ‘""’ is the only command line
argument in the sudoers file entry it means that
command is not allowed to be run with any arguments.
sudoedit Command line arguments to the sudoedit built-in command
should always be path names, so a forward slash (‘/’)
will not be matched by a wildcard.
Regular expressions
Starting with version 1.9.10, it is possible to use regular
expressions for path names and command line arguments. Regular
expressions are more expressive than shell-style wildcards and
are usually safer because they provide a greater degree of
control when matching. The type of regular expressions supported
by sudoers are POSIX extended regular expressions, similar to
those used by the egrep(1) utility. They are usually documented
in the regex(7) or re_format(7) manual, depending on the system.
As an extension, if the regular expression begins with “(?i)”, it
will be matched in a case-insensitive manner.
In sudoers, regular expressions must start with a ‘^’ character
and end with a ‘$’. This makes it explicit what is, or is not, a
regular expression. Either the path name, the command line
arguments or both may be regular expressions. Because the path
name and arguments are matched separately, it is even possible to
use wildcards for the path name and regular expressions for the
arguments. It is not possible to use a single regular expression
to match both the command and its arguments. Regular expressions
in sudoers are limited to 1024 characters.
There is no need to escape sudoers special characters in a
regular expression other than the pound sign (‘#’).
In the following example, user john can run the passwd(1) command
as root on any host but is not allowed to change root's password.
This kind of rule is impossible to express safely using
wildcards.
john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\
!/usr/bin/passwd root
It is also possible to use a regular expression in conjunction
with sudoedit rules. The following rule would give user bob the
ability to edit the /etc/motd, /etc/issue, and /etc/hosts files
only.
bob ALL = sudoedit ^/etc/(motd|issue|hosts)$
Regular expressions may also be used to match the command itself.
In this example, a regular expression is used to allow user sid
to run the /usr/sbin/groupadd, /usr/sbin/groupmod,
/usr/sbin/groupdel, /usr/sbin/useradd, /usr/sbin/usermod, and
/usr/sbin/userdel commands as root.
sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$
One disadvantage of using a regular expression to match the
command name is that it is not possible to match relative paths
such as ./useradd or ../sbin/useradd. This has security
implications when a regular expression is used for the command
name in conjunction with the negation operator, ‘!’, as such
rules can be trivially bypassed. Because of this, using a
negated regular expression for the command name is strongly
discouraged. This does not apply to negated commands that only
use a regular expression to match the command arguments. See
“Regular expressions in command names” below for more
information.
Including other files from within sudoers
It is possible to include other sudoers files from within the
sudoers file currently being parsed using the @include and
@includedir directives. For compatibility with sudo versions
prior to 1.9.1, #include and #includedir are also accepted.
An include file can be used, for example, to keep a site-wide
sudoers file in addition to a local, per-machine file. For the
sake of this example the site-wide sudoers file will be
/etc/sudoers and the per-machine one will be /etc/sudoers.local.
To include /etc/sudoers.local from within /etc/sudoers one would
use the following line in /etc/sudoers:
@include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the
current file (/etc/sudoers) and switch to /etc/sudoers.local.
Upon reaching the end of /etc/sudoers.local, the rest of
/etc/sudoers will be processed. Files that are included may
themselves include other files. A hard limit of 128 nested
include files is enforced to prevent include file loops.
Starting with version 1.9.1, the path to the include file may
contain white space if it is escaped with a backslash (‘\’).
Alternately, the entire path may be enclosed in double quotes
(""), in which case no escaping is necessary. To include a
literal backslash in the path, ‘\\’ should be used.
If the path to the include file is not fully-qualified (does not
begin with a ‘/’), it must be located in the same directory as
the sudoers file it was included from. For example, if
/etc/sudoers contains the line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the ‘%h’ escape, signifying the
short form of the host name. In other words, if the machine's
host name is “xerxes”, then
@include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes. Any
path name separator characters (‘/’) present in the host name
will be replaced with an underbar (‘_’) during expansion.
The @includedir directive can be used to create a sudoers.d
directory that the system package manager can drop sudoers file
rules into as part of package installation. For example, given:
@includedir /etc/sudoers.d
sudo will suspend processing of the current file and read each
file in /etc/sudoers.d, skipping file names that end in ‘~’ or
contain a ‘.’ character to avoid causing problems with package
manager or editor temporary/backup files.
Files are parsed in sorted lexical order. That is,
/etc/sudoers.d/01_first will be parsed before
/etc/sudoers.d/10_second. Be aware that because the sorting is
lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded
after /etc/sudoers.d/10_second. Using a consistent number of
leading zeroes in the file names can be used to avoid such
problems. After parsing the files in the directory, control
returns to the file that contained the @includedir directive.
Unlike files included via @include, visudo will not edit the
files in a @includedir directory unless one of them contains a
syntax error. It is still possible to run visudo with the -f
flag to edit the files directly, but this will not catch the
redefinition of an alias that is also present in a different
file.
Other special characters and reserved words
The pound sign (‘#’) is used to indicate a comment (unless it is
part of a #include directive or unless it occurs in the context
of a user name and is followed by one or more digits, in which
case it is treated as a user-ID). Both the comment character and
any text after it, up to the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a
match to succeed. It can be used wherever one might otherwise
use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias.
Attempting to define an alias named ALL will result in a syntax
error. Using ALL can be dangerous since in a command context, it
allows the user to run any command on the system.
The following option names permitted in an Option_Spec are also
considered reserved words: CHROOT, TIMEOUT, CWD, NOTBEFORE and
NOTAFTER. Attempting to define an alias with the same name as
one of the options will result in a syntax error.
An exclamation point (‘!’) can be used as a logical not operator
in a list or alias as well as in front of a Cmnd. This allows
one to exclude certain values. For the ‘!’ operator to be
effective, there must be something for it to exclude. For
example, to match all users except for root one would use:
ALL, !root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users.
This is different from a true “negation” operator.
Note, however, that using a ‘!’ in conjunction with the built-in
ALL alias to allow a user to run “all but a few” commands rarely
works as intended (see “SECURITY NOTES” below).
Long lines can be continued with a backslash (‘\’) as the last
character on the line.
White space between elements in a list as well as special
syntactic characters in a User Specification (‘=’, ‘:’, ‘(’, ‘)’)
is optional.
The following characters must be escaped with a backslash (‘\’)
when used as part of a word (e.g., a user name or host name):
‘!’, ‘=’, ‘:’, ‘,’, ‘(’, ‘)’, ‘\’.
sudo's behavior can be modified by Default_Entry lines, as
explained earlier. A list of all supported Defaults parameters,
grouped by type, are listed below.
Boolean Flags:
always_query_group_plugin
If a group_plugin is configured, use it to
resolve groups of the form ‘%group’ as long as
there is not also a system group of the same
name. Normally, only groups of the form
‘%:group’ are passed to the group_plugin. This
flag is off by default.
always_set_home If enabled, sudo will set the HOME environment
variable to the home directory of the target
user (which is the runas_default user unless
the -u option is used). This flag is largely
obsolete and has no effect unless the env_reset
flag has been disabled or HOME is present in
the env_keep list, both of which are strongly
discouraged. This flag is off by default.
authenticate If set, users must authenticate themselves via
a password (or other means of authentication)
before they may run commands. This default may
be overridden via the PASSWD and NOPASSWD tags.
This flag is on by default.
case_insensitive_group
If enabled, group names in sudoers will be
matched in a case insensitive manner. This may
be necessary when users are stored in LDAP or
AD. This flag is on by default.
case_insensitive_user
If enabled, user names in sudoers will be
matched in a case insensitive manner. This may
be necessary when groups are stored in LDAP or
AD. This flag is on by default.
closefrom_override
If set, the user may use the -C option which
overrides the default starting point at which
sudo begins closing open file descriptors.
This flag is off by default.
compress_io If set, and sudo is configured to log a
command's input or output, the I/O logs will be
compressed using zlib. This flag is on by
default when sudo is compiled with zlib
support.
exec_background By default, sudo runs a command as the
foreground process as long as sudo itself is
running in the foreground. When the
exec_background flag is enabled and the command
is being run in a pseudo-terminal (due to I/O
logging or the use_pty flag), the command will
be run as a background process. Attempts to
read from the controlling terminal (or to
change terminal settings) will result in the
command being suspended with the SIGTTIN signal
(or SIGTTOU in the case of terminal settings).
If this happens when sudo is a foreground
process, the command will be granted the
controlling terminal and resumed in the
foreground with no user intervention required.
The advantage of initially running the command
in the background is that sudo need not read
from the terminal unless the command explicitly
requests it. Otherwise, any terminal input
must be passed to the command, whether it has
required it or not (the kernel buffers
terminals so it is not possible to tell whether
the command really wants the input). This is
different from historic sudo behavior or when
the command is not being run in a pseudo-
terminal.
For this to work seamlessly, the operating
system must support the automatic restarting of
system calls. Unfortunately, not all operating
systems do this by default, and even those that
do may have bugs. For example, macOS fails to
restart the tcgetattr(3) and tcsetattr(3)
functions (this is a bug in macOS).
Furthermore, because this behavior depends on
the command stopping with the SIGTTIN or
SIGTTOU signals, programs that catch these
signals and suspend themselves with a different
signal (usually SIGTOP) will not be
automatically foregrounded. Some versions of
the linux su(1) command behave this way. This
flag is off by default.
This setting is only supported by version 1.8.7
or higher. It has no effect unless I/O logging
is enabled or the use_pty flag is enabled.
env_editor If set, visudo will use the value of the
SUDO_EDITOR, VISUAL or EDITOR environment
variables before falling back on the default
editor list. visudo is typically run as root
so this flag may allow a user with visudo
privileges to run arbitrary commands as root
without logging. An alternative is to place a
colon-separated list of “safe” editors int the
editor setting. visudo will then only use
SUDO_EDITOR, VISUAL or EDITOR if they match a
value specified in editor. If the env_reset
flag is enabled, the SUDO_EDITOR, VISUAL and/or
EDITOR environment variables must be present in
the env_keep list for the env_editor flag to
function when visudo is invoked via sudo. This
flag is on by default.
env_reset If set, sudo will run the command in a minimal
environment containing the TERM, PATH, HOME,
MAIL, SHELL, LOGNAME, USER and SUDO_*
variables. Any variables in the caller's
environment or in the file specified by the
restricted_env_file setting that match the
env_keep and env_check lists are then added,
followed by any variables present in the file
specified by the env_file setting (if any).
The contents of the env_keep and env_check
lists, as modified by global Defaults
parameters in sudoers, are displayed when sudo
is run by root with the -V option. If the
secure_path setting is enabled, its value will
be used for the PATH environment variable.
This flag is on by default.
fast_glob Normally, sudo uses the glob(3) function to do
shell-style globbing when matching path names.
However, since it accesses the file system,
glob(3) can take a long time to complete for
some patterns, especially when the pattern
references a network file system that is
mounted on demand (auto mounted). The
fast_glob flag causes sudo to use the
fnmatch(3) function, which does not access the
file system to do its matching. The
disadvantage of fast_glob is that it is unable
to match relative paths such as ./ls or
../bin/ls. This has security implications when
path names that include globbing characters are
used with the negation operator, ‘!’, as such
rules can be trivially bypassed. As such, this
flag should not be used when the sudoers file
contains rules that contain negated path names
which include globbing characters. This flag
is off by default.
log_passwords Most programs that require a user's password
will disable echo before reading the password
to avoid displaying the plaintext password on
the screen. However, if terminal input is
being logged (see “I/O LOGGING”), the password
will still be present in the I/O log. If the
log_passwords option is disabled, sudoers will
attempt to prevent passwords from being logged.
It does this by using the regular expressions
in passprompt_regex to match a password prompt
in the terminal output buffer. When a match is
found, input characters in the I/O log will be
replaced with ‘*’ until either a line feed or
carriage return is found in the terminal input
or a new terminal output buffer is received.
If, however, a program displays characters as
the user types (such as sudo when pwfeedback is
set), only the first character of the password
will be replaced in the I/O log. This option
has no effect unless log_input or log_ttyin are
also set. This flag is on by default.
This setting is only supported by version
1.9.10 or higher.
fqdn Set this flag if you want to put fully
qualified host names in the sudoers file when
the local host name (as returned by the
‘hostname’ command) does not contain the domain
name. In other words, instead of myhost you
would use myhost.mydomain.edu. You may still
use the short form if you wish (and even mix
the two). This flag is only effective when the
“canonical” host name, as returned by the
getaddrinfo(3) or gethostbyname(3) function, is
a fully-qualified domain name. This is usually
the case when the system is configured to use
DNS for host name resolution.
If the system is configured to use the
/etc/hosts file in preference to DNS, the
“canonical” host name may not be fully-
qualified. The order that sources are queried
for host name resolution is usually specified
in the /etc/nsswitch.conf, /etc/netsvc.conf,
/etc/host.conf, or, in some cases,
/etc/resolv.conf file. In the /etc/hosts file,
the first host name of the entry is considered
to be the “canonical” name; subsequent names
are aliases that are not used by sudoers. For
example, the following hosts file line for the
machine “xyzzy” has the fully-qualified domain
name as the “canonical” host name, and the
short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not
formatted properly, the fqdn flag will not be
effective if it is queried before DNS.
Beware that when using DNS for host name
resolution, turning on fqdn requires sudoers to
make DNS lookups which renders sudo unusable if
DNS stops working (for example if the machine
is disconnected from the network). Just like
with the hosts file, you must use the
“canonical” name as DNS knows it. That is, you
may not use a host alias (CNAME entry) due to
performance issues and the fact that there is
no way to get all aliases from DNS.
This flag is off by default.
ignore_audit_errors
Allow commands to be run even if sudoers cannot
write to the audit log. If enabled, an audit
log write failure is not treated as a fatal
error. If disabled, a command may only be run
after the audit event is successfully written.
This flag is only effective on systems for
which sudoers supports audit logging, including
FreeBSD, Linux, macOS, and Solaris. This flag
is on by default.
ignore_dot If set, sudo will ignore "." or "" (both
denoting the current directory) in the PATH
environment variable; the PATH itself is not
modified. This flag is off by default.
ignore_iolog_errors
Allow commands to be run even if sudoers cannot
write to the I/O log (local or remote). If
enabled, an I/O log write failure is not
treated as a fatal error. If disabled, the
command will be terminated if the I/O log
cannot be written to. This flag is off by
default.
ignore_logfile_errors
Allow commands to be run even if sudoers cannot
write to the log file. If enabled, a log file
write failure is not treated as a fatal error.
If disabled, a command may only be run after
the log file entry is successfully written.
This flag only has an effect when sudoers is
configured to use file-based logging via the
logfile setting. This flag is on by default.
ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will
be skipped. This is intended for sites that
wish to prevent the usage of local sudoers
files so that only LDAP is used. This thwarts
the efforts of rogue operators who would
attempt to add roles to /etc/sudoers. When
this flag is enabled, /etc/sudoers does not
even need to exist. Since this flag tells sudo
how to behave when no specific LDAP entries
have been matched, this sudoOption is only
meaningful for the ‘cn=defaults’ section. This
flag is off by default.
ignore_unknown_defaults
If set, sudo will not produce a warning if it
encounters an unknown Defaults entry in the
sudoers file or an unknown sudoOption in LDAP.
This flag is off by default.
insults If set, sudo will insult users when they enter
an incorrect password. This flag is off by
default.
log_allowed If set, sudoers will log commands allowed by
the policy to the system audit log (where
supported) as well as to syslog and/or a log
file. This flag is on by default.
This setting is only supported by version
1.8.29 or higher.
log_denied If set, sudoers will log commands denied by the
policy to the system audit log (where
supported) as well as to syslog and/or a log
file. This flag is on by default.
This setting is only supported by version
1.8.29 or higher.
log_exit_status If set, sudoers will log the exit value of
commands that are run to syslog and/or a log
file. If a command was terminated by a signal,
the signal name is logged as well. This flag
is off by default.
This setting is only supported by version 1.9.8
or higher.
log_host If set, the host name will be included in log
entries written to the file configured by the
logfile setting. This flag is off by default.
log_input If set, sudo will run the command in a pseudo-
terminal (if sudo was run from a terminal) and
log all user input. If the standard input is
not connected to the user's terminal, due to
I/O redirection or because the command is part
of a pipeline, that input is also logged. For
more information about I/O logging, see the
“I/O LOGGING” section. This flag is off by
default.
log_output If set, sudo will run the command in a pseudo-
terminal (if sudo was run from a terminal) and
log all output that is sent to the user's
terminal, the standard output or the standard
error. If the standard output or standard
error is not connected to the user's terminal,
due to I/O redirection or because the command
is part of a pipeline, that output is also
logged. For more information about I/O
logging, see the “I/O LOGGING” section. This
flag is off by default.
log_server_keepalive
If set, sudo will enable the TCP keepalive
socket option on the connection to the log
server. This enables the periodic transmission
of keepalive messages to the server. If the
server does not respond to a message, the
connection will be closed and the running
command will be terminated unless the
ignore_iolog_errors flag (I/O logging enabled)
or the ignore_log_errors flag (I/O logging
disabled) is set. This flag is on by default.
This setting is only supported by version 1.9.0
or higher.
log_server_verify
If set, the server certificate received during
the TLS handshake must be valid and it must
contain either the server name (from
log_servers) or its IP address. If either of
these conditions is not met, the TLS handshake
will fail. This flag is on by default.
This setting is only supported by version 1.9.0
or higher.
log_stderr If set, sudo will log the standard error if it
is not connected to the user's terminal. This
can be used to log output to a pipe or
redirected to a file. This flag is off by
default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag
is set.
log_stdin If set, sudo will log the standard input if it
is not connected to the user's terminal. This
can be used to log input from a pipe or
redirected from a file. This flag is off by
default but is enabled when either the
log_input flag or the LOG_INPUT command tag is
set.
log_stdout If set, sudo will log the standard output if it
is not connected to the user's terminal. This
can be used to log output to a pipe or
redirected to a file. This flag is off by
default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag
is set.
log_subcmds If set, sudoers will log when a command spawns
a child process and executes a program using
the execve(2), execl(3), execle(3), execlp(3),
execv(3), execvp(3), execvpe(3), or system(3)
library functions. For example, if a shell is
run by sudo, the individual commands run via
the shell will be logged. This flag is off by
default.
The log_subcmds flag uses the same underlying
mechanism as the intercept setting. Some
commands may not work properly when log_subcmds
is enabled, due to the way it intercepts sub-
commands. See “Preventing shell escapes” for
more information on what systems support this
option and its limitations. This setting is
only supported by version 1.9.8 or higher and
is incompatible with SELinux RBAC support
unless the system supports seccomp(2) filter
mode.
log_ttyin If set, sudo will run the command in a pseudo-
terminal and log user keystrokes sent to the
user's terminal, if one is present. This flag
is off by default but is enabled when either
the log_input flag or the LOG_INPUT command tag
is set. If no terminal is present, for example
when running a remote command using ssh(1),
this flag will have no effect.
log_ttyout If set, sudo will run the command in a pseudo-
terminal and log all output displayed on the
user's terminal, if one is present. This flag
is off by default but is enabled when either
the log_output flag or the LOG_OUTPUT command
tag is set. If no terminal is present, for
example when running a remote command using
ssh(1), this flag will have no effect.
log_year If set, the four-digit year will be logged in
the (non-syslog) sudo log file. This flag is
off by default.
long_otp_prompt When validating with a One Time Password (OTP)
scheme such as S/Key or OPIE, a two-line prompt
is used to make it easier to cut and paste the
challenge to a local window. It's not as
pretty as the default but some people find it
more convenient. This flag is off by default.
mail_all_cmnds Send mail to the mailto user every time a user
attempts to run a command via sudo (this
includes sudoedit). No mail will be sent if
the user runs sudo with the -l or -v option
unless there is an authentication error and the
mail_badpass flag is also set. This flag is
off by default.
mail_always Send mail to the mailto user every time a user
runs sudo. This flag is off by default.
mail_badpass Send mail to the mailto user if the user
running sudo does not enter the correct
password. If the command the user is
attempting to run is not permitted by sudoers
and one of the mail_all_cmnds, mail_always,
mail_no_host, mail_no_perms or mail_no_user
flags are set, this flag will have no effect.
This flag is off by default.
mail_no_host If set, mail will be sent to the mailto user if
the invoking user exists in the sudoers file,
but is not allowed to run commands on the
current host. This flag is off by default.
mail_no_perms If set, mail will be sent to the mailto user if
the invoking user is allowed to use sudo but
the command they are trying is not listed in
their sudoers file entry or is explicitly
denied. This flag is off by default.
mail_no_user If set, mail will be sent to the mailto user if
the invoking user is not in the sudoers file.
This flag is on by default.
match_group_by_gid
By default, sudoers will look up each group the
user is a member of by group-ID to determine
the group name (this is only done once). The
resulting list of the user's group names is
used when matching groups listed in the sudoers
file. This works well on systems where the
number of groups listed in the sudoers file is
larger than the number of groups a typical user
belongs to. On systems where group lookups are
slow, where users may belong to a large number
of groups, or where the number of groups listed
in the sudoers file is relatively small, it may
be prohibitively expensive and running commands
via sudo may take longer than normal. On such
systems it may be faster to use the
match_group_by_gid flag to avoid resolving the
user's group-IDs to group names. In this case,
sudoers must look up any group name listed in
the sudoers file and use the group-ID instead
of the group name when determining whether the
user is a member of the group.
If match_group_by_gid is enabled, group
database lookups performed by sudoers will be
keyed by group name as opposed to group-ID. On
systems where there are multiple sources for
the group database, it is possible to have
conflicting group names or group-IDs in the
local /etc/group file and the remote group
database. On such systems, enabling or
disabling match_group_by_gid can be used to
choose whether group database queries are
performed by name (enabled) or ID (disabled),
which may aid in working around group entry
conflicts.
The match_group_by_gid flag has no effect when
sudoers data is stored in LDAP. This flag is
off by default.
This setting is only supported by version
1.8.18 or higher.
intercept If set, all commands run via sudo will behave
as if the INTERCEPT tag has been set, unless
overridden by an NOINTERCEPT tag. Some
commands may not work properly when intercept
is enabled, due to the way it intercept sub-
commands. See the description of INTERCEPT and
NOINTERCEPT above as well as the “Preventing
shell escapes” section at the end of this
manual. This flag is off by default.
This setting is only supported by version 1.9.8
or higher and is incompatible with SELinux RBAC
support unless the system supports seccomp(2)
filter mode.
intercept_allow_setid
On most systems, the dynamic loader will ignore
LD_PRELOAD (or the equivalent) when running
set-user-ID and set-group-ID programs,
effectively disabling intercept mode. To
prevent this from happening, sudoers will not
permit a set-user-ID or set-group-ID program to
be run in intercept mode unless
intercept_allow_setid is enable. This flag has
no effect unless the intercept flag is enabled
or the INTERCEPT tag has been set for the
command. This flag is on by default when the
intercept_type option is set to trace,
otherwise it default to off.
This setting is only supported by version 1.9.8
or higher.
intercept_authenticate
If set, commands run by an intercepted process
must be authenticated when the user's time
stamp is not current. For example, if a shell
is run with intercept enabled, as soon as the
invoking user's time stamp is out of date,
subsequent commands will need to be
authenticated. This flag has no effect unless
the intercept flag is enabled or the INTERCEPT
tag has been set for the command. This flag is
off by default.
This setting is only supported by version 1.9.8
or higher.
intercept_verify If set, sudo will attempt to verify that a
command run in intercept mode has the expected
path name, command line arguments and
environment.
The process will be stopped after execve(2) has
completed but before the new command has had a
chance to run. To verify the command, sudo
will read the command's path from
/proc/PID/exe, the command line arguments and
environment from the process's memory, and
compare them against the arguments that were
passed to execve(2). In the event of a
mismatch, the command will be sent a SIGKILL
signal and terminated.
This can help prevent a time of check versus
time of use issue with intercept mode where the
execve(2) arguments could be altered after the
sudoers policy check. The checks can only be
performed if the proc(5) file system is
available. This flag has no effect unless the
intercept flag is enabled or the INTERCEPT tag
has been set for the command and the
intercept_type option is set to trace.
This setting is incompatible with programs that
change their root directory via chroot(2). If
a program changes its root directory, path
names will no longer match those seen by the
sudo parent process and sub-commands will be
terminated before they have a chance to run.
This flag is on by default.
This setting is only supported by version
1.9.12 or higher.
netgroup_tuple If set, netgroup lookups will be performed
using the full netgroup tuple: host name, user
name, and domain (if one is set).
Historically, sudo only matched the user name
and domain for netgroups used in a User_List
and only matched the host name and domain for
netgroups used in a Host_List. This flag is
off by default.
noexec If set, all commands run via sudo will behave
as if the NOEXEC tag has been set, unless
overridden by an EXEC tag. See the description
of EXEC and NOEXEC above as well as the
“Preventing shell escapes” section at the end
of this manual. This flag is off by default.
noninteractive_auth
If set, authentication will be attempted even
in non-interactive mode (when sudo's -n option
is specified). This allows authentication
methods that don't require user interaction to
succeed. Authentication methods that require
input from the user's terminal will still fail.
If disabled, authentication will not be
attempted in non-interactive mode. This flag
is off by default.
This setting is only supported by version
1.9.10 or higher.
pam_acct_mgmt On systems that use PAM for authentication,
sudo will perform PAM account validation for
the invoking user by default. The actual
checks performed depend on which PAM modules
are configured. If enabled, account validation
will be performed regardless of whether or not
a password is required. This flag is on by
default.
This setting is only supported by version
1.8.28 or higher.
pam_rhost On systems that use PAM for authentication,
sudo will set the PAM remote host value to the
name of the local host when the pam_rhost flag
is enabled. On Linux systems, enabling
pam_rhost may result in DNS lookups of the
local host name when PAM is initialized. On
Solaris versions prior to Solaris 8, pam_rhost
must be enabled if pam_ruser is also enabled to
avoid a crash in the Solaris PAM
implementation.
This flag is off by default on systems other
than Solaris.
This setting is only supported by version 1.9.0
or higher.
pam_ruser On systems that use PAM for authentication,
sudo will set the PAM remote user value to the
name of the user that invoked sudo when the
pam_ruser flag is enabled. This flag is on by
default.
This setting is only supported by version 1.9.0
or higher.
pam_session On systems that use PAM for authentication,
sudo will create a new PAM session for the
command to be run in. Unless sudo is given the
-i or -s options, PAM session modules are run
with the “silent” flag enabled. This prevents
last login information from being displayed for
every command on some systems. Disabling
pam_session may be needed on older PAM
implementations or on operating systems where
opening a PAM session changes the utmp or wtmp
files. If PAM session support is disabled,
resource limits may not be updated for the
command being run. If pam_session,
pam_setcred, and use_pty are disabled,
log_servers has not been set and I/O logging
has not been configured, sudo will execute the
command directly instead of running it as a
child process. This flag is on by default.
This setting is only supported by version 1.8.7
or higher.
pam_setcred On systems that use PAM for authentication,
sudo will attempt to establish credentials for
the target user by default, if supported by the
underlying authentication system. One example
of a credential is a Kerberos ticket. If
pam_session, pam_setcred, and use_pty are
disabled, log_servers has not been set and I/O
logging has not been configured, sudo will
execute the command directly instead of running
it as a child process. This flag is on by
default.
This setting is only supported by version 1.8.8
or higher.
pam_silent If set, PAM authentication will be performed in
silent mode. This prevents PAM authentication
modules from generating output. In some cases,
this may suppress important information about
why authentication failed. For example, PAM
modules such as pam_faillock will only display
a warning if pam_silent is disabled. This flag
is on by default.
This setting is only supported by version
1.8.16 or higher.
passprompt_override
If set, the prompt specified by passprompt or
the SUDO_PROMPT environment variable will
always be used and will replace the prompt
provided by a PAM module or other
authentication method. This flag is off by
default.
path_info Normally, sudo will tell the user when a
command could not be found in their PATH
environment variable. Some sites may wish to
disable this as it could be used to gather
information on the location of executables that
the normal user does not have access to. The
disadvantage is that if the executable is
simply not in the user's PATH, sudo will tell
the user that they are not allowed to run it,
which can be confusing. This flag is on by
default.
preserve_groups By default, sudo will initialize the group
vector to the list of groups the target user is
in. When preserve_groups is set, the user's
existing group vector is left unaltered. The
real and effective group-IDs, however, are
still set to match the target user. This flag
is off by default.
pwfeedback By default, sudo reads the password like most
other Unix programs, by turning off echo until
the user hits the return (or enter) key. Some
users become confused by this as it appears to
them that sudo has hung at this point. When
pwfeedback is set, sudo will provide visual
feedback when the user presses a key. This
does have a security impact as an onlooker may
be able to determine the length of the password
being entered. This flag is off by default.
requiretty If set, sudo will only run when the user is
logged in to a real tty. When this flag is
set, sudo can only be run from a login session
and not via other means such as cron(8) or cgi-
bin scripts. This flag is off by default.
root_sudo If set, root is allowed to run sudo too.
Disabling this prevents users from “chaining”
sudo commands to get a root shell by doing
something like ‘sudo sudo /bin/sh’. Note,
however, that turning off root_sudo will also
prevent root from running sudoedit. Disabling
root_sudo provides no real additional security;
it exists purely for historical reasons. This
flag is on by default.
rootpw If set, sudo will prompt for the root password
instead of the password of the invoking user
when running a command or editing a file. This
flag is off by default.
runas_allow_unknown_id
If enabled, allow matching of runas user and
group IDs that are not present in the password
or group databases. In addition to explicitly
matching unknown user or group IDs in a
Runas_List, this option also allows the ALL
alias to match unknown IDs. This flag is off
by default.
This setting is only supported by version
1.8.30 or higher. Older versions of sudo
always allowed matching of unknown user and
group IDs.
runas_check_shell
If enabled, sudo will only run commands as a
user whose shell appears in the /etc/shells
file, even if the invoking user's Runas_List
would otherwise permit it. If no /etc/shells
file is present, a system-dependent list of
built-in default shells is used. On many
operating systems, system users such as “bin”,
do not have a valid shell and this flag can be
used to prevent commands from being run as
those users. This flag is off by default.
This setting is only supported by version
1.8.30 or higher.
runaspw If set, sudo will prompt for the password of
the user defined by the runas_default option
(defaults to root) instead of the password of
the invoking user when running a command or
editing a file. This flag is off by default.
set_home If enabled and sudo is invoked with the -s
option, the HOME environment variable will be
set to the home directory of the target user
(which is the runas_default user unless the -u
option is used). This flag is largely obsolete
and has no effect unless the env_reset flag has
been disabled or HOME is present in the
env_keep list, both of which are strongly
discouraged. This flag is off by default.
set_logname Normally, sudo will set the LOGNAME and USER
environment variables to the name of the target
user (the user specified by runas_default
unless the -u option is given). However, since
some programs (including the RCS revision
control system) use LOGNAME to determine the
real identity of the user, it may be desirable
to change this behavior. This can be done by
negating the set_logname option. The
set_logname option will have no effect if the
env_reset option has not been disabled and the
env_keep list contains LOGNAME or USER. This
flag is on by default.
set_utmp When enabled, sudo will create an entry in the
utmp (or utmpx) file when a pseudo-terminal is
allocated. A pseudo-terminal is allocated by
sudo when it is running in a terminal and one
or more of the log_input, log_output,
log_stdin, log_stdout, log_stderr, log_ttyin,
log_ttyout, or use_pty flags is enabled. By
default, the new entry will be a copy of the
user's existing utmp entry (if any), with the
tty, time, type, and pid fields updated. This
flag is on by default.
setenv Allow the user to disable the env_reset option
from the command line via the -E option.
Additionally, environment variables set via the
command line are not subject to the
restrictions imposed by env_check, env_delete,
or env_keep. As such, only trusted users
should be allowed to set variables in this
manner. This flag is off by default.
shell_noargs If set and sudo is invoked with no arguments it
acts as if the -s option had been given. That
is, it runs a shell as root (the shell is
determined by the SHELL environment variable if
it is set, falling back on the shell listed in
the invoking user's /etc/passwd entry if not).
This flag is off by default.
stay_setuid Normally, when sudo executes a command the real
and effective user-IDs are set to the target
user (root by default). This option changes
that behavior such that the real user-ID is
left as the invoking user's user-ID. In other
words, this makes sudo act as a set-user-ID
wrapper. This can be useful on systems that
disable some potentially dangerous
functionality when a program is run set-user-
ID. This option is only effective on systems
that support either the setreuid(2) or
setresuid(2) system call. This flag is off by
default.
sudoedit_checkdir
If set, sudoedit will check all directory
components of the path to be edited for
writability by the invoking user. Symbolic
links will not be followed in writable
directories and sudoedit will refuse to edit a
file located in a writable directory. These
restrictions are not enforced when sudoedit is
run by root. On some systems, if all directory
components of the path to be edited are not
readable by the target user, sudoedit will be
unable to edit the file. This flag is on by
default.
This setting was first introduced in version
1.8.15 but initially suffered from a race
condition. The check for symbolic links in
writable intermediate directories was added in
version 1.8.16.
sudoedit_follow By default, sudoedit will not follow symbolic
links when opening files. The sudoedit_follow
option can be enabled to allow sudoedit to open
symbolic links. It may be overridden on a per-
command basis by the FOLLOW and NOFOLLOW tags.
This flag is off by default.
This setting is only supported by version
1.8.15 or higher.
syslog_pid When logging via syslog(3), include the process
ID in the log entry. This flag is off by
default.
This setting is only supported by version
1.8.21 or higher.
targetpw If set, sudo will prompt for the password of
the user specified by the -u option (defaults
to the value of runas_default) instead of the
password of the invoking user when running a
command or editing a file. This flag precludes
the use of a user-ID not listed in the passwd
database as an argument to the -u option. This
flag is off by default.
tty_tickets If set, users must authenticate on a per-tty
basis. With this flag enabled, sudo will use a
separate record in the time stamp file for each
terminal. If disabled, a single record is used
for all login sessions.
This option has been superseded by the
timestamp_type option.
umask_override If set, sudo will set the umask as specified in
the sudoers file without modification. This
makes it possible to specify a umask in the
sudoers file that is more permissive than the
user's own umask and matches historical
behavior. If umask_override is not set, sudo
will set the umask to be the union of the
user's umask and what is specified in sudoers.
This flag is off by default.
use_netgroups If set, netgroups (prefixed with ‘+’), may be
used in place of a user or host. For LDAP-
based sudoers, netgroup support requires an
expensive sub-string match on the server unless
the NETGROUP_BASE directive is present in the
/etc/ldap.conf file. If netgroups are not
needed, this option can be disabled to reduce
the load on the LDAP server. This flag is on
by default.
use_pty If set, and sudo is running in a terminal, the
command will be run in a new pseudo-terminal.
If the sudo process is not attached to a
terminal, use_pty has no effect.
A malicious program run under sudo may be
capable of injecting commands into the user's
terminal or running a background process that
retains access to the user's terminal device
even after the main program has finished
executing. By running the command in a
separate pseudo-terminal, this attack is no
longer possible.
A side effect of running the command in a new
pseudo-terminal is that input will be passed to
the command even if it is non-interactive.
This means that, for example, keys pressed
while a non-interactive command is running will
be consumed by sudo instead of being passed to
the shell after the command exits.
This flag is on by default for sudo 1.9.14 and
above.
user_command_timeouts
If set, the user may specify a timeout on the
command line. If the timeout expires before
the command has exited, the command will be
terminated. If a timeout is specified both in
the sudoers file and on the command line, the
smaller of the two timeouts will be used. See
the Timeout_Spec section for a description of
the timeout syntax. This flag is off by
default.
This setting is only supported by version
1.8.20 or higher.
utmp_runas If set, sudo will store the name of the runas
user when updating the utmp (or utmpx) file.
By default, sudo stores the name of the
invoking user. This flag is off by default.
visiblepw By default, sudo will refuse to run if the user
must enter a password but it is not possible to
disable echo on the terminal. If the visiblepw
flag is set, sudo will prompt for a password
even when it would be visible on the screen.
This makes it possible to run things like ‘ssh
somehost sudo ls’ since by default, ssh(1) does
not allocate a tty when running a command.
This flag is off by default.
Integers:
closefrom Before it executes a command, sudo will close
all open file descriptors other than standard
input, standard output, and standard error
(file descriptors 0-2). The closefrom option
can be used to specify a different file
descriptor at which to start closing. The
default is 3.
command_timeout The maximum amount of time a command is allowed
to run before it is terminated. See the
Timeout_Spec section for a description of the
timeout syntax.
This setting is only supported by version
1.8.20 or higher.
log_server_timeout
The maximum amount of time to wait when
connecting to a log server or waiting for a
server response. See the Timeout_Spec section
for a description of the timeout syntax. The
default value is 30 seconds.
This setting is only supported by version 1.9.0
or higher.
maxseq The maximum sequence number that will be
substituted for the ‘%{seq}’ escape in the I/O
log file (see the iolog_dir description below
for more information). While the value
substituted for ‘%{seq}’ is in base 36, maxseq
itself should be expressed in decimal. Values
larger than 2176782336 (which corresponds to
the base 36 sequence number “ZZZZZZ”) will be
silently truncated to 2176782336. The default
value is 2176782336.
Once the local sequence number reaches the
value of maxseq, it will “roll over” to zero,
after which sudoers will truncate and reuse any
existing I/O log path names.
This setting is only supported by version 1.8.7
or higher.
passwd_tries The number of tries a user gets to enter
his/her password before sudo logs the failure
and exits. The default is 3.
syslog_maxlen On many systems, syslog(3) has a relatively
small log buffer. IETF RFC 5424 states that
syslog servers must support messages of at
least 480 bytes and should support messages up
to 2048 bytes. By default, sudoers creates log
messages up to 980 bytes which corresponds to
the historic BSD syslog implementation which
used a 1024 byte buffer to store the message,
date, hostname, and program name. To prevent
syslog messages from being truncated, sudoers
will split up log messages that are larger than
syslog_maxlen bytes. When a message is split,
additional parts will include the string
“(command continued)” after the user name and
before the continued command line arguments.
This setting is only supported by version
1.8.19 or higher.
Integers that can be used in a boolean context:
loglinelen Number of characters per line for the file log.
This value is used to decide when to wrap lines
for nicer log files. This has no effect on the
syslog log file, only the file log. The
default is 80 (use 0 or negate the option to
disable word wrap).
passwd_timeout Number of minutes before the sudo password
prompt times out, or 0 for no timeout. The
timeout may include a fractional component if
minute granularity is insufficient, for example
2.5. The default is 5.
timestamp_timeout
Number of minutes that can elapse before sudo
will ask for a password again. The timeout may
include a fractional component if minute
granularity is insufficient, for example 2.5.
The default is 5. Set this to 0 to always
prompt for a password. If set to a value less
than 0 the user's time stamp will not expire
until the system is rebooted. This can be used
to allow users to create or delete their own
time stamps via ‘sudo -v’ and ‘sudo -k’
respectively.
umask File mode creation mask to use when running the
command. Negate this option or set it to 0777
to prevent sudoers from changing the umask.
Unless the umask_override flag is set, the
actual umask will be the union of the user's
umask and the value of the umask setting, which
defaults to 0022. This guarantees that sudo
never lowers the umask when running a command.
If umask is explicitly set in sudoers, it will
override any umask setting in PAM or
login.conf. If umask is not set in sudoers,
the umask specified by PAM or login.conf will
take precedence. The umask setting in PAM is
not used for sudoedit, which does not create a
new PAM session.
Strings:
cmddenial_message
It set, sudo will display this message when a
user is denied access to run the specified
command, but is listed in the sudoers file for
the host. This can be used to provide
additional, site-specific information to the
user when a command is denied by the security
policy. It does not override the standard
warning the user receives when a command is
denied.
authfail_message Message that is displayed after a user fails to
authenticate. The message may include the ‘%d’
escape which will expand to the number of
failed password attempts. If set, it overrides
the default message, “%d incorrect password
attempt(s)”.
badpass_message Message that is displayed if a user enters an
incorrect password. The default is “Sorry, try
again.” unless insults are enabled.
editor A colon (‘:’) separated list of editor path
names used by sudoedit and visudo. For
sudoedit, this list is used to find an editor
when none of the SUDO_EDITOR, VISUAL or EDITOR
environment variables are set to an editor that
exists and is executable. For visudo, it is
used as a white list of allowed editors; visudo
will choose the editor that matches the user's
SUDO_EDITOR, VISUAL or EDITOR environment
variable if possible, or the first editor in
the list that exists and is executable if not.
Unless invoked as sudoedit, sudo does not
preserve the SUDO_EDITOR, VISUAL or EDITOR
environment variables unless they are present
in the env_keep list or the env_reset option is
disabled. The default is /usr/bin/vi.
intercept_type The underlying mechanism used by the intercept
and log_subcmds options. It has the following
possible values:
dso Preload a dynamic shared object (shared
library) that intercepts the execve(2),
execl(3), execle(3), execlp(3),
execv(3), execvp(3), execvpe(3), and
system(3) library functions. A value
of dso is incompatible with sudo's
SELinux RBAC support.
trace Use ptrace(2) to intercept the
execve(2) system call. This is only
supported on Linux systems where
seccomp(2) filtering is enabled. If
the
/proc/sys/kernel/seccomp/actions_avail
file is missing or does not contain a
“trap” element, setting intercept_type
to trace will have no effect and dso
will be used instead.
The default is to use trace if it is supported
by the system and dso if it is not.
iolog_dir The top-level directory to use when
constructing the path name for the input/output
log directory. Only used if the log_input or
log_output options are enabled or when the
LOG_INPUT or LOG_OUTPUT tags are present for a
command. The session sequence number, if any,
is stored in the directory. The default is
/var/log/sudo-io.
The following percent (‘%’) escape sequences
are supported:
%{seq}
expanded to a monotonically increasing
base-36 sequence number, such as 0100A5,
where every two digits are used to form a
new directory, e.g., 01/00/A5
%{user}
expanded to the invoking user's login
name
%{group}
expanded to the name of the invoking
user's real group-ID
%{runas_user}
expanded to the login name of the user
the command will be run as (e.g., root)
%{runas_group}
expanded to the group name of the user
the command will be run as (e.g., wheel)
%{hostname}
expanded to the local host name without
the domain name
%{command}
expanded to the base name of the command
being run
In addition, any escape sequences supported by
the system's strftime(3) function will be
expanded.
To include a literal ‘%’ character, the string
‘%%’ should be used.
Any path name separator characters (‘/’)
present in the user, group or host name will be
replaced with an underbar (‘_’) during
expansion.
iolog_file The path name, relative to iolog_dir, in which
to store input/output logs when the log_input
or log_output options are enabled or when the
LOG_INPUT or LOG_OUTPUT tags are present for a
command. iolog_file may contain directory
components. The default is ‘%{seq}’.
See the iolog_dir option above for a list of
supported percent (‘%’) escape sequences.
In addition to the escape sequences, path names
that end in six or more Xs will have the Xs
replaced with a unique combination of digits
and letters, similar to the mktemp(3) function.
If the path created by concatenating iolog_dir
and iolog_file already exists, the existing I/O
log file will be truncated and overwritten
unless iolog_file ends in six or more Xs.
iolog_flush If set, sudo will flush I/O log data to disk
after each write instead of buffering it. This
makes it possible to view the logs in real-time
as the program is executing but may
significantly reduce the effectiveness of I/O
log compression. This flag is off by default.
This setting is only supported by version
1.8.20 or higher.
iolog_group The group name to look up when setting the
group-ID on new I/O log files and directories.
If iolog_group is not set, the primary group-ID
of the user specified by iolog_user is used.
If neither iolog_group nor iolog_user are set,
I/O log files and directories are created with
group-ID 0.
This setting is only supported by version
1.8.19 or higher.
iolog_mode The file mode to use when creating I/O log
files. Mode bits for read and write
permissions for owner, group, or other are
honored, everything else is ignored. The file
permissions will always include the owner read
and write bits, even if they are not present in
the specified mode. When creating I/O log
directories, search (execute) bits are added to
match the read and write bits specified by
iolog_mode. Defaults to 0600 (read and write
by user only).
This setting is only supported by version
1.8.19 or higher.
iolog_user The user name to look up when setting the user
and group-IDs on new I/O log files and
directories. If iolog_group is set, it will be
used instead of the user's primary group-ID.
By default, I/O log files and directories are
created with user and group-ID 0.
This setting can be useful when the I/O logs
are stored on a Network File System (NFS)
share. Having a dedicated user own the I/O log
files means that sudoers does not write to the
log files as user-ID 0, which is usually not
permitted by NFS.
This setting is only supported by version
1.8.19 or higher.
lecture_status_dir
The directory in which sudo stores per-user
lecture status files. Once a user has received
the lecture, a zero-length file is created in
this directory so that sudo will not lecture
the user again. This directory should not be
cleared when the system reboots. The default
is /var/db/sudo/lectured.
log_server_cabundle
The path to a certificate authority bundle
file, in PEM format, to use instead of the
system's default certificate authority database
when authenticating the log server. The
default is to use the system's default
certificate authority database. This setting
has no effect unless log_servers is set and the
remote log server is secured with TLS.
This setting is only supported by version 1.9.0
or higher.
log_server_peer_cert
The path to the sudo client's certificate file,
in PEM format. This setting is required when
the remote log server is secured with TLS and
client certificate validation is enabled. For
sudo_logsrvd, client certificate validation is
controlled by the tls_checkpeer option, which
defaults to false.
This setting is only supported by version 1.9.0
or higher.
log_server_peer_key
The path to the sudo client's private key file,
in PEM format. This setting is required when
the remote log server is secured with TLS and
client certificate validation is enabled. For
sudo_logsrvd, client certificate validation is
controlled by the tls_checkpeer flag, which
defaults to false.
This setting is only supported by version 1.9.0
or higher.
mailsub Subject of the mail sent to the mailto user.
The escape ‘%h’ will expand to the host name of
the machine. Default is “*** SECURITY
information for %h ***”.
noexec_file As of sudo version 1.8.1 this option is no
longer supported. The path to the noexec file
should now be set in the sudo.conf(5) file.
pam_askpass_service
On systems that use PAM for authentication,
this is the service name used when the -A
option is specified. The default value is
either ‘sudo’ or ‘sudo’, depending on whether
or not the -i option is also specified. See
the description of pam_service for more
information.
This setting is only supported by version 1.9.9
or higher.
pam_login_service
On systems that use PAM for authentication,
this is the service name used when the -i
option is specified. The default value is
‘sudo’. See the description of pam_service for
more information.
This setting is only supported by version 1.8.8
or higher.
pam_service On systems that use PAM for authentication, the
service name specifies the PAM policy to apply.
This usually corresponds to an entry in the
pam.conf file or a file in the /etc/pam.d
directory. The default value is ‘sudo’.
This setting is only supported by version 1.8.8
or higher.
passprompt The default prompt to use when asking for a
password; can be overridden via the -p option
or the SUDO_PROMPT environment variable. The
following percent (‘%’) escape sequences are
supported:
%H expanded to the local host name including
the domain name (only if the machine's
host name is fully qualified or the fqdn
option is set)
%h expanded to the local host name without
the domain name
%p expanded to the user whose password is
being asked for (respects the rootpw,
targetpw and runaspw flags in sudoers)
%U expanded to the login name of the user
the command will be run as (defaults to
root)
%u expanded to the invoking user's login
name
%% two consecutive ‘%’ characters are
collapsed into a single ‘%’ character
On systems that use PAM for authentication,
passprompt will only be used if the prompt
provided by the PAM module matches the string
“Password: ” or “username's Password: ”. This
ensures that the passprompt setting does not
interfere with challenge-response style
authentication. The passprompt_override flag
can be used to change this behavior.
The default value is ‘Password: ’.
runas_default The default user to run commands as if the -u
option is not specified on the command line.
This defaults to root.
sudoers_locale Locale to use when parsing the sudoers file,
logging commands, and sending email. Changing
the locale may affect how sudoers is
interpreted. Defaults to ‘C’.
timestamp_type sudoers uses per-user time stamp files for
credential caching. The timestamp_type option
can be used to specify the type of time stamp
record used. It has the following possible
values:
global A single time stamp record is used for
all of a user's login sessions,
regardless of the terminal or parent
process ID. An additional record is
used to serialize password prompts when
sudo is used multiple times in a
pipeline, but this does not affect
authentication.
ppid A single time stamp record is used for
all processes with the same parent
process ID (usually the shell).
Commands run from the same shell (or
other common parent process) will not
require a password for
timestamp_timeout minutes (5 by
default). Commands run via sudo with a
different parent process ID, for
example from a shell script, will be
authenticated separately.
tty One time stamp record is used for each
terminal, which means that a user's
login sessions are authenticated
separately. If no terminal is present,
the behavior is the same as ppid.
Commands run from the same terminal
will not require a password for
timestamp_timeout minutes (5 by
default).
kernel The time stamp is stored in the kernel
as an attribute of the terminal device.
If no terminal is present, the behavior
is the same as ppid. Negative
timestamp_timeout values are not
supported and positive values are
limited to a maximum of 60 minutes.
This is currently only supported on
OpenBSD.
The default value is tty.
This setting is only supported by version
1.8.21 or higher.
timestampdir The directory in which sudo stores its time
stamp files. This directory should be cleared
when the system reboots. The default is
/run/sudo/ts.
timestampowner The owner of the lecture status directory, time
stamp directory and all files stored therein.
The default is root.
Strings that can be used in a boolean context:
admin_flag The admin_flag option specifies the path to a file
that is created the first time a user that is a
member of the sudo or admin groups runs sudo. Only
available if sudo is configured with the
--enable-admin-flag option. The default value is
~/.sudo_as_admin_successful.
env_file The env_file option specifies the fully qualified
path to a file containing variables to be set in
the environment of the program being run. Entries
in this file should either be of the form
‘VARIABLE=value’ or ‘export VARIABLE=value’. The
value may optionally be enclosed in single or
double quotes. Variables in this file are only
added if the variable does not already exist in the
environment. This file is considered to be part of
the security policy, its contents are not subject
to other sudo environment restrictions such as
env_keep and env_check.
exempt_group Users in this group are exempt from password and
PATH requirements. The group name specified should
not include a ‘%’ prefix. This is not set by
default.
fdexec Determines whether sudo will execute a command by
its path or by an open file descriptor. It has the
following possible values:
always Always execute by file descriptor.
never Never execute by file descriptor.
digest_only
Only execute by file descriptor if the
command has an associated digest in the
sudoers file.
The default value is digest_only. This avoids a
time of check versus time of use race condition
when the command is located in a directory writable
by the invoking user.
fdexec will change the first element of the
argument vector for scripts ($0 in the shell) due
to the way the kernel runs script interpreters.
Instead of being a normal path, it will refer to a
file descriptor. For example, /dev/fd/4 on Solaris
and /proc/self/fd/4 on Linux. A workaround is to
use the SUDO_COMMAND environment variable instead.
The fdexec setting is only used when the command is
matched by path name. It has no effect if the
command is matched by the built-in ALL alias.
This setting is only supported by version 1.8.20 or
higher. If the operating system does not support
the fexecve(2) system call, this setting has no
effect.
group_plugin A string containing a sudoers group plugin with
optional arguments. The string should consist of
the plugin path, either fully-qualified or relative
to the /usr/local/libexec/sudo directory, followed
by any configuration arguments the plugin requires.
These arguments (if any) will be passed to the
plugin's initialization function. If arguments are
present, the string must be enclosed in double
quotes ("").
On 64-bit systems, if the plugin is present but
cannot be loaded, sudoers will look for a 64-bit
version and, if it exists, load that as a fallback.
The exact rules for this vary by system. On
Solaris, if the plugin is stored in a directory
ending in “lib”, sudoers will create a fallback
path by appending “/64” to the directory name;
/usr/local/lib/group_plugin.so becomes
/usr/local/lib/64/group_plugin.so. On Linux, a
directory ending in “lib” will be transformed to
“lib64” as the fallback path;
/usr/local/lib/group_plugin.so becomes
/usr/local/lib64/group_plugin.so. On all other
systems, the fallback path is generated by adding a
“64” before the file extension; group_plugin.so
becomes group_plugin64.so.
On AIX systems, the plugin may be either a shared
object ending in ‘.so’ or an archive file
containing a shared object ending in ‘.a’ with the
name of the shared object in parentheses at the
end.
For more information see “GROUP PROVIDER PLUGINS”.
lecture This option controls when a short lecture will be
printed along with the password prompt. It has the
following possible values:
always Always lecture the user.
never Never lecture the user.
once Only lecture the user the first time they
run sudo.
If no value is specified, a value of once is
implied. Negating the option results in a value of
never being used. The default value is once.
lecture_file Path to a file containing an alternate sudo lecture
that will be used in place of the standard lecture
if the named file exists. By default, sudo uses a
built-in lecture.
listpw This option controls when a password will be
required when a user runs sudo with the -l option.
It has the following possible values:
all All the user's sudoers file entries for the
current host must have the NOPASSWD flag set
to avoid entering a password.
always
The user must always enter a password to use
the -l option.
any At least one of the user's sudoers file
entries for the current host must have the
NOPASSWD flag set to avoid entering a
password.
never
The user need never enter a password to use
the -l option.
If no value is specified, a value of any is
implied. Negating the option results in a value of
never being used. The default value is any.
log_format The event log format. Supported log formats are:
json Currently, this is an alias for json_pretty.
In a future version of sudo, json will be
equivalent to json_compact. JSON log entries
contain the full user details as well as the
execution environment if the command was
allowed.
json_compact
Log events in “compact” (minified) JSON
format. Each event is written as a separate
JSON object on single line without extraneous
white space. Due to limitations of the
protocol, JSON events sent via syslog may be
truncated.
json_pretty
Log events in “pretty” JSON format. When
logging to a file, the entire file is treated
as a single JSON object consisting of
multiple events, each event spanning multiple
lines. When logging via syslog, there is no
difference between the json_pretty and
json_compact formats.
sudo Log events in traditional sudo-style format,
see “EVENT LOGGING” for details.
This setting affects logs sent via syslog(3) as
well as the file specified by the logfile setting,
if any. The default value is sudo.
logfile Path to the sudo log file (not the syslog log
file). Setting a path turns on logging to a file;
negating this option turns it off. By default,
sudo logs via syslog.
mailerflags Flags to use when invoking mailer. Defaults to -t.
mailerpath Path to mail program used to send warning mail
(negate to prevent sudo from sending mail).
Defaults to the path to sendmail found at configure
time.
mailfrom Address to use for the “from” address when sending
warning and error mail. The address should be
enclosed in double quotes ("") to protect against
sudo interpreting the ‘@’ sign. Defaults to the
name of the user running sudo.
mailto Address to send warning and error mail to (negate
to prevent sudo from sending mail). The address
should be enclosed in double quotes ("") to protect
against sudo interpreting the ‘@’ sign. Defaults
to root.
rlimit_as The maximum size to which the process's address
space may grow (in bytes), if supported by the
operating system. See “Resource limits” for more
information.
rlimit_core The largest size core dump file that may be created
(in bytes). See “Resource limits” for more
information. Defaults to 0 (no core dump created).
rlimit_cpu The maximum amount of CPU time that the process may
use (in seconds). See “Resource limits” for more
information.
rlimit_data The maximum size of the data segment for the
process (in bytes). See “Resource limits” for more
information.
rlimit_fsize The largest size file that the process may create
(in bytes). See “Resource limits” for more
information.
rlimit_locks The maximum number of locks that the process may
establish, if supported by the operating system.
See “Resource limits” for more information.
rlimit_memlock
The maximum size that the process may lock in
memory (in bytes), if supported by the operating
system. See “Resource limits” for more
information.
rlimit_nofile
The maximum number of files that the process may
have open. See “Resource limits” for more
information.
rlimit_nproc The maximum number of processes that the user may
run simultaneously. See “Resource limits” for more
information.
rlimit_rss The maximum size to which the process's resident
set size may grow (in bytes). See “Resource
limits” for more information.
rlimit_stack The maximum size to which the process's stack may
grow (in bytes). See “Resource limits” for more
information.
restricted_env_file
The restricted_env_file option specifies the fully
qualified path to a file containing variables to be
set in the environment of the program being run.
Entries in this file should either be of the form
‘VARIABLE=value’ or ‘export VARIABLE=value’. The
value may optionally be enclosed in single or
double quotes. Variables in this file are only
added if the variable does not already exist in the
environment. Unlike env_file, the file's contents
are not trusted and are processed in a manner
similar to that of the invoking user's environment.
If env_reset is enabled, variables in the file will
only be added if they are matched by either the
env_check or env_keep list. If env_reset is
disabled, variables in the file are added as long
as they are not matched by the env_delete list. In
either case, the contents of restricted_env_file
are processed before the contents of env_file.
runchroot If set, sudo will use this value for the root
directory when running a command. The special
value “*” will allow the user to specify the root
directory via sudo's -R option. See the
“Chroot_Spec” section for more details.
It is only possible to use runchroot as a command-
specific Defaults setting if the command exists
with the same path both inside and outside the
chroot jail. This restriction does not apply to
global, host, or user-based Defaults settings or to
a Cmnd_Spec that includes a Chroot_Spec.
This setting is only supported by version 1.9.3 or
higher.
runcwd If set, sudo will use this value for the working
directory when running a command. The special
value “*” will allow the user to specify the
working directory via sudo's -D option. See the
“Chdir_Spec” section for more details.
This setting is only supported by version 1.9.3 or
higher.
secure_path If set, sudo will use this value in place of the
user's PATH environment variable. This option can
be used to reset the PATH to a known good value
that contains directories for system administrator
commands such as /usr/sbin.
Users in the group specified by the exempt_group
option are not affected by secure_path. This
option is not set by default.
syslog Syslog facility if syslog is being used for logging
(negate to disable syslog logging). Defaults to
authpriv.
The following syslog facilities are supported:
authpriv (if your OS supports it), auth, daemon,
user, local0, local1, local2, local3, local4,
local5, local6, and local7.
syslog_badpri
Syslog priority to use when the user is not allowed
to run a command or when authentication is
unsuccessful. Defaults to alert.
The following syslog priorities are supported:
alert, crit, debug, emerg, err, info, notice,
warning, and none. Negating the option or setting
it to a value of none will disable logging of
unsuccessful commands.
syslog_goodpri
Syslog priority to use when the user is allowed to
run a command and authentication is successful.
Defaults to notice.
See syslog_badpri for the list of supported syslog
priorities. Negating the option or setting it to a
value of none will disable logging of successful
commands.
verifypw This option controls when a password will be
required when a user runs sudo with the -v option.
It has the following possible values:
all All the user's sudoers file entries for the
current host must have the NOPASSWD flag
set to avoid entering a password.
always The user must always enter a password to
use the -v option.
any At least one of the user's sudoers file
entries for the current host must have the
NOPASSWD flag set to avoid entering a
password.
never The user need never enter a password to use
the -v option.
If no value is specified, a value of all is
implied. Negating the option results in a value of
never being used. The default value is all.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the
user's environment unless they are considered
“safe”. For all variables except TZ, “safe”
means that the variable's value does not
contain any ‘%’ or ‘/’ characters. This can be
used to guard against printf-style format
vulnerabilities in poorly-written programs.
The TZ variable is considered unsafe if any of
the following are true:
• It consists of a fully-qualified path name,
optionally prefixed with a colon (‘:’), that
does not match the location of the zoneinfo
directory.
• It contains a .. path element.
• It contains white space or non-printable
characters.
• It is longer than the value of PATH_MAX.
The argument may be a double-quoted, space-
separated list or a single value without
double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the ‘=’,
‘+=’, ‘-=’, and ‘!’ operators respectively.
Regardless of whether the env_reset option is
enabled or disabled, variables specified by
env_check will be preserved in the environment
if they pass the aforementioned check. The
global list of environment variables to check
is displayed when sudo is run by root with the
-V option.
env_delete Environment variables to be removed from the
user's environment when the env_reset option is
not in effect. The argument may be a double-
quoted, space-separated list or a single value
without double-quotes. The list can be
replaced, added to, deleted from, or disabled
by using the ‘=’, ‘+=’, ‘-=’, and ‘!’ operators
respectively. The global list of environment
variables to remove is displayed when sudo is
run by root with the -V option. Many operating
systems will remove potentially dangerous
variables from the environment of any set-user-
ID process (such as sudo).
env_keep Environment variables to be preserved in the
user's environment when the env_reset option is
in effect. This allows fine-grained control
over the environment sudo-spawned processes
will receive. The argument may be a double-
quoted, space-separated list or a single value
without double-quotes. The list can be
replaced, added to, deleted from, or disabled
by using the ‘=’, ‘+=’, ‘-=’, and ‘!’ operators
respectively. The global list of variables to
keep is displayed when sudo is run by root with
the -V option.
Preserving the HOME environment variable has
security implications since many programs use
it when searching for configuration or data
files. Adding HOME to env_keep may enable a
user to run unrestricted commands via sudo and
is strongly discouraged. Users wishing to edit
files with sudo should run sudoedit (or sudo
-e) to get their accustomed editor
configuration instead of invoking the editor
directly.
log_servers A list of one or more servers to use for remote
event and I/O log storage, separated by white
space. Log servers must be running
sudo_logsrvd or another service that implements
the protocol described by sudo_logsrv.proto(5).
Server addresses should be of the form
“host[:port][(tls)]”. The host portion may be
a host name, an IPv4 address, or an IPv6
address in square brackets.
If the optional tls flag is present, the
connection will be secured with Transport Layer
Security (TLS) version 1.2 or 1.3. Versions of
TLS prior to 1.2 are not supported.
If a port is specified, it may either be a port
number or a well-known service name as defined
by the system service name database. If no
port is specified, port 30343 will be used for
plaintext connections and port 30344 will be
used for TLS connections.
When log_servers is set, event log data will be
logged both locally (see the syslog and
log_file settings) as well as remotely, but I/O
log data will only be logged remotely. If
multiple hosts are specified, they will be
attempted in reverse order. If no log servers
are available, the user will not be able to run
a command unless either the ignore_iolog_errors
flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled)
is set. Likewise, if the connection to the log
server is interrupted while sudo is running,
the command will be terminated unless the
ignore_iolog_errors flag (I/O logging enabled)
or the ignore_log_errors flag (I/O logging
disabled) is set.
This setting is only supported by version 1.9.0
or higher.
passprompt_regex A list of POSIX extended regular expressions
used to match password prompts in the terminal
output. As an extension, if the regular
expression begins with “(?i)”, it will be
matched in a case-insensitive manner. Each
regular expression is limited to 1024
characters. This option is only used when
log_passwords has been disabled. The default
value is “[Pp]assword[: ]*”
This setting is only supported by version
1.9.10 or higher.
The sudoers plugin supports its own plugin interface to allow
non-Unix group lookups which can query a group source other than
the standard Unix group database. This can be used to implement
support for the nonunix_group syntax described earlier.
Group provider plugins are specified via the group_plugin
setting. The argument to group_plugin should consist of the
plugin path, either fully-qualified or relative to the
/usr/local/libexec/sudo directory, followed by any configuration
options the plugin requires. These options (if specified) will
be passed to the plugin's initialization function. If options
are present, the string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
group_file
The group_file plugin supports an alternate group file that
uses the same syntax as the /etc/group file. The path to
the group file should be specified as an option to the
plugin. For example, if the group file to be used is
/etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
system_group
The system_group plugin supports group lookups via the
standard C library functions getgrnam(3) and getgrid(3).
This plugin can be used in instances where the user belongs
to groups not present in the user's supplemental group
vector. This plugin takes no options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in
sudo_plugin(5).
sudoers can log events in either JSON or sudo format, this
section describes the sudo log format. Depending on sudoers
configuration, sudoers can log events via syslog(3), to a local
log file, or both. The log format is almost identical in both
cases. Any control characters present in the log data are
formatted in octal with a leading ‘#’ character. For example, a
horizontal tab is stored as ‘#011’ and an embedded carriage
return is stored as ‘#015’. In addition, space characters in the
command path are stored as ‘#040’. Command line arguments that
contain spaces are enclosed in single quotes (''). This makes it
possible to distinguish multiple command line arguments from a
single argument that contains spaces. Literal single quotes and
backslash characters (‘\’) in command line arguments are escaped
with a backslash.
Accepted command log entries
Commands that sudo runs are logged using the following format
(split into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; CHROOT=chroot ; \
PWD=cwd ; USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
date The date the command was run. Typically, this is
in the format “MMM, DD, HH:MM:SS”. If logging via
syslog(3), the actual date format is controlled by
the syslog daemon. If logging to a file and the
log_year option is enabled, the date will also
include the year.
hostname The name of the host sudo was run on. This field
is only present when logging via syslog(3).
progname The name of the program, usually sudo or sudoedit.
This field is only present when logging via
syslog(3).
username The login name of the user who ran sudo.
ttyname The short name of the terminal (e.g., “console”,
“tty01”, or “pts/0”) sudo was run on, or “unknown”
if there was no terminal present.
chroot The root directory that the command was run in, if
one was specified.
cwd The current working directory that sudo was run in.
runasuser The user the command was run as.
runasgroup The group the command was run as if one was
specified on the command line.
logid An I/O log identifier that can be used to replay
the command's output. This is only present when
the log_input or log_output option is enabled.
env_vars A list of environment variables specified on the
command line, if specified.
command The actual command that was executed, including any
command line arguments.
Messages are logged using the locale specified by sudoers_locale,
which defaults to the ‘C’ locale.
Denied command log entries
If the user is not allowed to run the command, the reason for the
denial will follow the user name. Possible reasons include:
user NOT in sudoers
The user is not listed in the sudoers file.
user NOT authorized on host
The user is listed in the sudoers file but is not allowed to
run commands on the host.
command not allowed
The user is listed in the sudoers file for the host but they
are not allowed to run the specified command.
3 incorrect password attempts
The user failed to enter their password after 3 tries. The
actual number of tries will vary based on the number of failed
attempts and the value of the passwd_tries option.
a password is required
The -n option was specified but a password was required.
sorry, you are not allowed to set the following environment
variables
The user specified environment variables on the command line
that were not allowed by sudoers.
Error log entries
If an error occurs, sudoers will log a message and, in most
cases, send a message to the administrator via email. Possible
errors include:
parse error in /etc/sudoers near line N
sudoers encountered an error when parsing the specified file.
In some cases, the actual error may be one line above or below
the line number listed, depending on the type of error.
problem with defaults entries
The sudoers file contains one or more unknown Defaults
settings. This does not prevent sudo from running, but the
sudoers file should be checked using visudo.
timestamp owner (username): No such user
The time stamp directory owner, as specified by the
timestampowner setting, could not be found in the password
database.
unable to open/read /etc/sudoers
The sudoers file could not be opened for reading. This can
happen when the sudoers file is located on a remote file system
that maps user-ID 0 to a different value. Normally, sudoers
tries to open the sudoers file using group permissions to avoid
this problem. Consider either changing the ownership of
/etc/sudoers or adding an argument like “sudoers_uid=N” (where
‘N’ is the user-ID that owns the sudoers file) to the end of
the sudoers Plugin line in the sudo.conf(5) file.
unable to open /etc/sudoers
The /etc/sudoers file is missing.
/etc/sudoers is not a regular file
The /etc/sudoers file exists but is not a regular file or
symbolic link.
/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change
the sudoers file owner, add “sudoers_uid=N” (where ‘N’ is the
user-ID that owns the sudoers file) to the sudoers Plugin line
in the sudo.conf(5) file.
/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to
it. The sudoers file must not be world-writable, the default
file mode is 0440 (readable by owner and group, writable by
none). The default mode may be changed via the “sudoers_mode”
option to the sudoers Plugin line in the sudo.conf(5) file.
/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to
change the sudoers file group ownership, add “sudoers_gid=N”
(where ‘N’ is the group-ID that owns the sudoers file) to the
sudoers Plugin line in the sudo.conf(5) file.
unable to open /run/sudo/ts/user-ID
sudoers was unable to read or create the user's time stamp
file. This can happen when timestampowner is set to a user
other than root and the mode on /run/sudo is not searchable by
group or other. The default mode for /run/sudo is 0711.
unable to write to /run/sudo/ts/user-ID
sudoers was unable to write to the user's time stamp file.
/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than
timestampowner. This can occur when the value of
timestampowner has been changed. sudoers will ignore the time
stamp directory until the owner is corrected.
/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be
writable only by timestampowner. The default mode for the time
stamp directory is 0700. sudoers will ignore the time stamp
directory until the mode is corrected.
Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date,
hostname, and progname fields are added by the system's syslog(3)
function, not sudoers itself. As such, they may vary in format
on different systems.
The maximum size of syslog messages varies from system to system.
The syslog_maxlen setting can be used to change the maximum
syslog message size from the default value of 980 bytes. For
more information, see the description of syslog_maxlen.
Notes on logging to a file
If the logfile option is set, sudoers will log to a local file,
such as /var/log/sudo. When logging to a file, sudoers uses a
format similar to syslog(3), with a few important differences:
1. The progname field is not present.
2. The hostname is only logged if the log_host option is
enabled.
3. The date does not include the year unless the log_year
option is enabled.
4. Lines that are longer than loglinelen characters (80 by
default) are word-wrapped and continued on the next line
with a four character indent. This makes entries easier to
read for a human being, but makes it more difficult to use
grep(1) on the log files. If the loglinelen option is set
to 0 (or negated with a ‘!’), word wrap will be disabled.
When I/O logging is enabled, sudo will runs the command in a
pseudo-terminal, logging user input and/or output, depending on
which sudoers flags are enabled. There are five distinct types
of I/O that can be logged, each with a corresponding sudoers
flag.
Type Flag Description
terminal input log_ttyin keystrokes entered by the user
terminal output log_ttyout command output displayed to the
screen
standard input log_stdin input from a pipe or a file
standard output log_stdout output to a pipe or a file
standard error log_stderr output to a pipe or a file
In addition to flags described the above, the log_input flag and
LOG_INPUT command tag set both log_ttyin and log_stdin. The
log_output flag and LOG_OUTPUT command tag set log_ttyout,
log_stdout, and log_stderr.
To capture terminal input and output, sudo run the command in a
pseudo-terminal, logging the input and output before passing it
on to the user. To capture the standard input, standard output
or standard error, sudo uses a pipe to interpose itself between
the input or output stream, logging the I/O before passing it to
the other end of the pipe.
I/O can be logged either to the local machine or to a remote log
server. For local logs, I/O is logged to the directory specified
by the iolog_dir option (/var/log/sudo-io by default) using a
unique session ID that is included in the sudo log line, prefixed
with ‘TSID=’. The iolog_file option may be used to control the
format of the session ID. For remote logs, the log_servers
setting is used to specify one or more log servers running
sudo_logsrvd or another server that implements the protocol
described by sudo_logsrv.proto(5).
I/O logging pitfals
When logging standard input, anything sent to the standard input
will be consumed, regardless of whether or not the command run
via sudo is actively reading the standard input. This may have
unexpected results when using sudo in a shell script that expects
to process the standard input. For example, given the following
shell script:
#!/bin/sh
sudo echo testing
echo done
It will behave as expected when the script is passed to the shell
as a an argument:
$ sh test.sh
testing
done
However, if the script is passed to the shell on the standard
input, the ‘sudo echo testing’ command will consume the rest of
the script. This means that the ‘echo done’ statement is never
executed.
$ sh -s < test.sh
testing
There are several ways to work around this problem:
1. Redirect the standard input from /dev/null when running a
command via sudo that does not need to read the standard
input.
sudo echo testing < /dev/null
2. Pass the script to the shell by path name instead of via the
standard input.
sh test.sh
3. Disable logging the standard input for commands that do not
need to read the standard input.
Defaults!/bin/echo !log_stdin
Depending on the command, it may not be desirable to log the
standard input or standard output. For example, I/O logging of
commands that send or receive large amount of data via the
standard output or standard input such as rsync(1) and tar(1)
could fill up the log file system with superfluous data. It is
possible to disable logging of the standard input and standard
output for such commands as follows:
Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync
# Log input and output but omit stdin and stdout when copying files.
Defaults log_input, log_output
Defaults!COPY_CMDS !log_stdin, !log_stdout
However, be aware that using the log_input flag or the LOG_INPUT
command tag will also enable log_stdin. Likewise, the log_ouput
flag or the LOG_OUTPUT command tag will enable log_stdout and
log_stderr. Careful ordering of rules may be necessary to achieve
the results that you expect.
I/O log format
For both local and remote I/O logs, each log is stored in a
separate directory that contains the following files:
log A text file containing information about the command.
The first line consists of the following colon-
delimited fields: the time the command was run, the
name of the user who ran sudo, the name of the target
user, the name of the target group (optional), the
terminal that sudo was run from, and the number of
lines and columns of the terminal. The second and
third lines contain the working directory the command
was run from and the path name of the command itself
(with arguments if present).
log.json A JSON-formatted file containing information about the
command. This is similar to the log file but contains
additional information and is easily extensible. The
log.json file will be used by sudoreplay(8) in
preference to the log file if it exists. The file may
contain the following elements:
timestamp
A JSON object containing time the command was
run. It consists of two values, seconds and
nanoseconds.
columns
The number of columns of the terminal the command
ran on, or zero if no terminal was present.
command
The fully-qualified path of the command that was
run.
lines
The number of lines of the terminal the command
ran on, or zero if no terminal was present.
runargv
A JSON array representing the command's argument
vector as passed to the execve(2) system call.
runenv
A JSON array representing the command's
environment as passed to the execve(2) system
call.
rungid
The group ID the command ran as. This element is
only present when the user specifies a group on
the command line.
rungroup
The name of the group the command ran as. This
element is only present when the user specifies a
group on the command line.
runuid
The user ID the command ran as.
runuser
The name of the user the command ran as.
submitcwd
The current working directory at the time sudo
was run.
submithost
The name of the host the command was run on.
submituser
The name of the user who ran the command via
sudo.
ttyname
The path name of the terminal the user invoked
sudo from. If the command was run in a pseudo-
terminal, ttyname will be different from the
terminal the command actually ran in.
timing Timing information used to replay the session. Each
line consists of the I/O log entry type and amount of
time since the last entry, followed by type-specific
data. The I/O log entry types and their corresponding
type-specific data are:
0 standard input, number of bytes in the entry
1 standard output, number of bytes in the entry
2 standard error, number of bytes in the entry
3 terminal input, number of bytes in the entry
4 terminal output, number of bytes in the entry
5 window change, new number lines and columns
6 bug compatibility for sudo 1.8.7 terminal output
7 command suspend or resume, signal received
ttyin Raw input from the user's terminal, exactly as it was
received. This file is only present if the log_input
or log_ttyin flags are set and sudo was run from a
terminal. No post-processing is performed. For manual
viewing, you may wish to convert carriage return
characters in the log to line feeds. For example:
‘gunzip -c ttyin | tr "\r" "\n"’
stdin The standard input when no terminal is present, or
input redirected from a pipe or file. This file is
only present if the log_input or log_stdin flags are
set and the standard input is not connected to a
terminal.
ttyout Output from the pseudo-terminal (what the command
writes to the screen). Terminal-specific post-
processing is performed before the data is logged.
This means that, for example, line feeds are usually
converted to line feed/carriage return pairs and tabs
may be expanded to spaces. This file is only present
if the log_output or log_ttyout flags are set and sudo
was run from a terminal.
stdout The standard output when no terminal is present, or
output redirected to a pipe or file. This file is only
present if the log_output or log_stdout flags are set
and the standard output is not connected to a terminal.
stderr The standard error when no terminal is present, or
output redirected to a pipe or file. This file is only
present if the log_output or log_stderr flags are set
and the standard error is not connected to a terminal.
All files other than log are compressed in gzip format unless the
compress_io flag has been disabled. Due to buffering, it is not
normally possible to display the I/O logs in real-time as the
program is executing. The I/O log data will not be complete
until the program run by sudo has exited or has been terminated
by a signal. The iolog_flush flag can be used to disable
buffering, in which case I/O log data is written to disk as soon
as it is available. The output portion of an I/O log file can be
viewed with the sudoreplay(8) utility, which can also be used to
list or search the available logs.
User input may contain sensitive information such as passwords
(even if they are not echoed to the screen), which will be stored
in the log file unencrypted. In most cases, logging the command
output via log_output or LOG_OUTPUT is all that is required.
When logging input, consider disabling the log_passwords flag.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the
number of I/O logs. The simplest way to limit the number of I/O
is by setting the maxseq option to the maximum number of logs you
wish to store. Once the I/O log sequence number reaches maxseq,
it will be reset to zero and sudoers will truncate and reuse any
existing I/O logs.
/etc/sudo.conf Sudo front-end configuration
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
/var/log/sudo-io I/O log files
/run/sudo/ts Directory containing time stamps for
the sudoers security policy
/var/db/sudo/lectured Directory containing lecture status
files for the sudoers security policy
/etc/environment Initial environment for -i mode on AIX
and Linux systems
Below are example sudoers file entries. Admittedly, some of
these are a bit contrived. First, we allow a few environment
variables to pass and then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Other programs use HOME to locate configuration
# files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBADMIN = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = primary, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want
sudo to log via syslog(3) using the auth facility in all cases
and for commands to be run with the target user's home directory
as the working directory. We don't want to subject the full time
staff to the sudo lecture and we want to allow them to run
commands in a chroot(2) “sandbox” via the -R option. User
millert need not provide a password and we don't want to reset
the LOGNAME or USER environment variables when running commands
as root. Additionally, on the machines in the SERVERS
Host_Alias, we keep an additional local log file and make sure we
log the year in each log line since the log entries will be kept
around for several years. Lastly, we disable shell escapes for
the commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg
and /usr/bin/less). This will not effectively constrain users
with sudo ALL privileges.
# Override built-in defaults
Defaults syslog=auth,runcwd=~
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture,runchroot=*
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who
may run what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any
host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any
command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley, jwfox, and crawl) may run any
command on any host but they must authenticate themselves first
(since the entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS
alias (the networks 128.138.243.0, 128.138.204.0, and
128.138.242.0). Of those networks, only 128.138.204.0 has an
explicit netmask (in CIDR notation) indicating it is a class C
network. For the other networks in CSNETS, the local machine's
netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias
(the class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance.
Here, those are commands related to backups, killing processes,
the printing system, shutting down the system, and any commands
in the directory /usr/oper/bin/. One command in the DUMPS
Cmnd_Alias includes a sha224 digest,
/home/operator/bin/start_backups. This is because the directory
containing the script is writable by the operator user. If the
script is modified (resulting in a digest mismatch) it will no
longer be possible to run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as
themselves with any group in the ADMINGRP Runas_Alias (the adm
and oper groups).
The user pete is allowed to change anyone's password except for
root on the HPPA machines. Because command line arguments are
matched as a single, concatenated string, the ‘*’ wildcard will
match multiple words. This example assumes that passwd(1) does
not take multiple user names on the command line. On systems
with GNU getopt(3), options to passwd(1) may be specified after
the user argument. As a result, this rule will also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as
any user listed in the OP Runas_Alias (root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab
netgroup. sudo knows that “biglab” is a netgroup due to the ‘+’
prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the
printers as well as add and remove users, so they are allowed to
run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias
(oracle or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but
he is not allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those
in the SERVERS Host_Alias (primary, mail, www, and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any
commands in the directory /usr/bin/ except for those commands
belonging to the SU and SHELLS Cmnd_Aliases. While not
specifically mentioned in the rule, the commands in the PAGERS
Cmnd_Alias all reside in /usr/bin and have the noexec option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory
/usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to
kill hung processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN User_Alias (will,
wendy, and wim), may run any command as user www (which owns the
web pages) or simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the
CDROM Host_Alias (orion, perseus, hercules) without entering a
password. This is a bit tedious for users to type, so it is a
prime candidate for encapsulating in a shell script.
Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from ALL
using the ‘!’ operator. A user can trivially circumvent this by
copying the desired command to a different name and then
executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in
SU or SHELLS since he can simply copy those commands to a
different name, or use a shell escape from an editor or other
program. Therefore, these kind of restrictions should be
considered advisory at best (and reinforced by policy).
In general, if a user has sudo ALL there is nothing to prevent
them from creating their own program that gives them a root shell
(or making their own copy of a shell) regardless of any ‘!’
elements in the user specification.
[1mSecurity implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably
negate commands where the path name includes globbing (aka
wildcard) characters. This is because the C library's fnmatch(3)
function cannot resolve relative paths. While this is typically
only an inconvenience for rules that grant privileges, it can
result in a security issue for rules that subtract or revoke
privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run ‘/usr/bin/passwd root’ if fast_glob is
enabled by changing to /usr/bin and running ‘./passwd root’
instead.
Another potential issue is that when sudo executes the command,
it must use the command or path specified by the user instead of
a path listed in the sudoers file. This may lead to a time of
check versus time of use race condition.
Wildcards in command arguments
Command line arguments are matched as a single, concatenated
string. This mean a wildcard character such as ‘?’ or ‘*’ will
match across word boundaries, which may be unexpected. For
example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. A safer alternative is
to use a regular expression for matching command line arguments.
The above example can be rewritten as a regular expression:
%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$
The regular expression will only match a single file with a name
that begins with /var/log/messages and does not include any white
space in the name. It is often better to do command line
processing outside of the sudoers file in a scripting language
for anything non-trivial.
Regular expressions in command names
Using a regular expression to match a command name has the same
security implications as using the fast_glob option:
• It is not possible to reliably negate commands when the path
name is a regular expression.
• When sudo executes the command, it must use the command or
path specified by the user instead of a path listed in the
sudoers file. This may lead to a time of check versus time of
use race condition.
These issues do not apply to rules where only the command line
options are matched using a regular expression.
Preventing shell escapes
Once sudo executes a program, that program is free to do whatever
it pleases, including run other programs. This can be a security
issue since it is not uncommon for a program to allow shell
escapes, which lets a user bypass sudo's access control and
logging. Common programs that permit shell escapes include
shells (obviously), editors, paginators, mail, and terminal
programs.
There are four basic approaches to this problem:
restrict Avoid giving users access to commands that allow the
user to run arbitrary commands. Many editors have a
restricted mode where shell escapes are disabled,
though sudoedit is a better solution to running
editors via sudo. Due to the large number of programs
that offer shell escapes, restricting users to the set
of programs that do not is often unworkable.
intercept On most systems, sudo's intercept functionality can be
used to transparently intercept an attempt to run a
new command, allow or deny it based on sudoers rules,
and log the result. For example, this can be used to
restrict the commands run from within a privileged
shell or editor. However, not all programs operate
correctly when intercept is enabled.
There are two underlying mechanisms that may be used
to implement intercept mode: dso and trace. The
intercept_type setting can be used to select between
them.
The first mechanism, dso, overrides the standard C
library functions that are used to execute a command.
It does this by setting an environment variable
(usually LD_PRELOAD) to the path of a dynamic shared
object, or shared library, containing custom versions
of the execve(2), execl(3), execle(3), execlp(3),
execv(3), execvp(3), execvpe(3), and system(3) library
functions that connect back to sudo for a policy
decision. Note, however, that this applies only to
dynamically-linked executables. It is not possible to
intercept commands for statically-linked executables
or executables that run under binary emulation this
way. Because most dynamic loaders ignore LD_PRELOAD
(or the equivalent) when running set-user-ID and set-
group-ID programs, sudoers will not permit such
programs to be run in intercept mode by default. The
dso mechanism is incompatible with sudo's SELinux RBAC
support (but see below). SELinux disables LD_PRELOAD
by default and interferes with file descriptor
inheritance, which sudo relies on.
The second mechanism, trace, is available on Linux
systems that support seccomp(2) filtering. It uses
ptrace(2) and seccomp(2) to intercept the execve(2)
system call instead of pre-loading a dynamic shared
object. Both static and dynamic executables are
supported and it is compatible with sudo's SELinux
RBAC mode. Functions utilizing the execveat(2) system
call, such as fexecve(3), are not currently
intercepted. Programs that rely on ptrace(2)
themselves, such as debuggers and system call tracers
(such as strace(1) and truss(1)) will be unable to
function if intercept is enabled in trace mode. This
same restriction applies to the log_subcmds sudoers
option.
The intercept feature is known to work on Solaris,
*BSD, Linux, macOS, HP-UX 11.x and AIX 5.3 and above.
It should be supported on most operating systems that
support the LD_PRELOAD environment variable or an
equivalent. It is not possible to intercept shell
built-in commands or restrict the ability to read or
write sensitive files from within a shell.
To enable intercept mode on a per-command basis, use
the INTERCEPT tag as documented in the User
Specification section above. Here is that example
again:
chuck research = INTERCEPT: ALL
This allows user chuck to run any command on the
machine “research” in intercept mode. Any commands
run via shell escapes will be validated and logged by
sudo. If you are unsure whether or not your system is
capable of supporting intercept, you can always just
try it out and check whether or not external commands
run via a shell are logged when intercept is enabled.
There is an inherent race condition between when a
command is checked against sudoers rules and when it
is actually executed. If a user is allowed to run
arbitrary commands, they may be able to change the
execve(2) arguments in the program after the sudoers
policy check has completed but before the new command
is executed. Starting with version 1.9.12, the trace
method will verify that the command and its arguments
have not changed after execve(2) has completed but
before execution of the new program has had a chance
to run. This is not the case with the dso method.
See the description of the intercept_verify setting
for more information.
log There are two separate but related ways to log
additional commands. The first is to enable I/O
logging using the log_output flag. This will log the
command's output but will not create an event log
entry when the additional command is run. The second
is to enable the log_subcmds flag in sudoers which
will create an event log entry every time a new
command is run. If I/O logging is also enabled, the
log entry will include a time offset into the I/O log
to indicate when the command was run. This offset can
be passed to the sudoreplay(8) utility to replay the
I/O log at the exact moment when the command was run.
The log_subcmds flag uses the same mechanism as
intercept (see above) and has the same limitations.
noexec sudo's noexec functionality can be used to prevent a
program run by sudo from executing any other programs.
On most systems, it uses the same LD_PRELOAD mechanism
as intercept (see above) and thus the same caveats
apply. The noexec functionality is capable of
blocking execution of commands run via the execve(2),
execl(3), execle(3), execlp(3), exect(3), execv(3),
execveat(3), execvP(3), execvp(3), execvpe(3),
fexecve(3), popen(3), posix_spawn(3), posix_spawnp(3),
system(3), and wordexp(3) functions. On Linux, a
seccomp(2) filter is used to implement noexec. On
Solaris 10 and higher, noexec uses Solaris privileges
instead of the LD_PRELOAD environment variable.
To enable noexec for a command, use the NOEXEC tag as
documented in the User Specification section above.
Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and
/usr/bin/vi with noexec enabled. This will prevent
those two commands from executing other commands (such
as a shell). If you are unsure whether or not your
system is capable of supporting noexec you can always
just try it out and check whether shell escapes work
when noexec is enabled.
Restricting shell escapes is not a panacea. Programs running as
root are still capable of many potentially hazardous operations
(such as changing or overwriting files) that could lead to
unintended privilege escalation. In the specific case of an
editor, a safer approach is to give the user permission to run
sudoedit (see below).
Secure editing
The sudoers plugin includes sudoedit support which allows users
to securely edit files with the editor of their choice. As
sudoedit is a built-in command, it must be specified in the
sudoers file without a leading path. However, it may take
command line arguments just as a normal command does. Wildcards
used in sudoedit command line arguments are expected to be path
names, so a forward slash (‘/’) will not be matched by a
wildcard.
Unlike other sudo commands, the editor is run with the
permissions of the invoking user and with the environment
unmodified. More information may be found in the description of
the -e option in sudo(8).
For example, to allow user operator to edit the “message of the
day” file on any machine:
operator ALL = sudoedit /etc/motd
The operator user then runs sudoedit as follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a
temporary copy of /etc/motd. After the file has been edited,
/etc/motd will be updated with the contents of the temporary
copy.
Users should never be granted sudoedit permission to edit a file
that resides in a directory the user has write access to, either
directly or via a wildcard. If the user has write access to the
directory it is possible to replace the legitimate file with a
link to another file, allowing the editing of arbitrary files.
To prevent this, starting with version 1.8.16, symbolic links
will not be followed in writable directories and sudoedit will
refuse to edit a file located in a writable directory unless the
sudoedit_checkdir option has been disabled or the invoking user
is root. Additionally, in version 1.8.15 and higher, sudoedit
will refuse to open a symbolic link unless either the
sudoedit_follow option is enabled or the sudoedit command is
prefixed with the FOLLOW tag in the sudoers file.
Time stamp file checks
sudoers will check the ownership of its time stamp directory
(/run/sudo/ts by default) and ignore the directory's contents if
it is not owned by root or if it is writable by a user other than
root. Older versions of sudo stored time stamp files in /tmp;
this is no longer recommended as it may be possible for a user to
create the time stamp themselves on systems that allow
unprivileged users to change the ownership of files they create.
While the time stamp directory should be cleared at reboot time,
not all systems contain a /run or /var/run directory. To avoid
potential problems, sudoers will ignore time stamp files that
date from before the machine booted on systems where the boot
time is available.
Some systems with graphical desktop environments allow
unprivileged users to change the system clock. Since sudoers
relies on the system clock for time stamp validation, it may be
possible on such systems for a user to run sudo for longer than
timestamp_timeout by setting the clock back. To combat this,
sudoers uses a monotonic clock (which never moves backwards) for
its time stamps if the system supports it.
sudoers will not honor time stamps set far in the future. Time
stamps with a date greater than current_time + 2 * TIMEOUT will
be ignored and sudoers will log and complain.
If the timestamp_type option is set to “tty”, the time stamp
record includes the device number of the terminal the user
authenticated with. This provides per-terminal granularity but
time stamp records may still outlive the user's session.
Unless the timestamp_type option is set to “global”, the time
stamp record also includes the session ID of the process that
last authenticated. This prevents processes in different
terminal sessions from using the same time stamp record. On
systems where a process's start time can be queried, the start
time of the session leader is recorded in the time stamp record.
If no terminal is present or the timestamp_type option is set to
“ppid”, the start time of the parent process is used instead. In
most cases this will prevent a time stamp record from being
reused without the user entering a password when logging out and
back in again.
Versions 1.8.4 and higher of the sudoers plugin support a
flexible debugging framework that can help track down what the
plugin is doing internally if there is a problem. This can be
configured in the sudo.conf(5) file.
The sudoers plugin uses the same debug flag format as the sudo
front-end: subsystem@priority.
The priorities used by sudoers, in order of decreasing severity,
are: crit, err, warn, notice, diag, info, trace, and debug. Each
priority, when specified, also includes all priorities higher
than it. For example, a priority of notice would include debug
messages logged at notice and higher.
The following subsystems are used by the sudoers plugin:
alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias
processing
all matches every subsystem
audit BSM and Linux audit code
auth user authentication
defaults sudoers file Defaults settings
env environment handling
ldap LDAP-based sudoers
logging logging support
match matching of users, groups, hosts, and netgroups in the
sudoers file
netif network interface handling
nss network service switch handling in sudoers
parser sudoers file parsing
perms permission setting
plugin The equivalent of main for the plugin.
pty pseudo-terminal related code
rbtree redblack tree internals
sssd SSSD-based sudoers
util utility functions
For example:
Debug sudoers.so /var/log/sudoers_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3),
sudo.conf(5), sudo_plugin(5), sudoers.ldap(5),
sudoers_timestamp(5), sudo(8), visudo(8)
Many people have worked on sudo over the years; this version
consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS.md file in the sudo distribution
(https://www.sudo.ws/about/contributors/) for an exhaustive list
of people who have contributed to sudo.
The sudoers file should always be edited by the visudo utility
which locks the file and checks for syntax errors. If sudoers
contains syntax errors, sudo may refuse to run, which is a
serious problem if sudo is your only method of obtaining
superuser privileges. Recent versions of sudoers will attempt to
recover after a syntax error by ignoring the rest of the line
after encountering an error. Older versions of sudo will not run
if sudoers contains a syntax error.
When using netgroups of machines (as opposed to users), if you
store fully qualified host name in the netgroup (as is usually
the case), you either need to have the machine's host name be
fully qualified as returned by the hostname command or use the
fqdn option in sudoers.
If you believe you have found a bug in sudoers, you can either
file a bug report in the sudo bug database,
https://bugzilla.sudo.ws/, or open an issue at
https://github.com/sudo-project/sudo/issues. If you would prefer
to use email, messages may be sent to the sudo-workers mailing
list, https://www.sudo.ws/mailman/listinfo/sudo-workers (public)
or <[email protected]> (private).
Please not report security vulnerabilities through public GitHub
issues, Bugzilla or mailing lists. Instead, report them via
email to <[email protected]>. You may encrypt your message
with PGP if you would like, using the key found at
https://www.sudo.ws/dist/PGPKEYS.
Limited free support is available via the sudo-users mailing
list, see https://www.sudo.ws/mailman/listinfo/sudo-users to
subscribe or search the archives.
sudo is provided “AS IS” and any express or implied warranties,
including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose are
disclaimed. See the LICENSE.md file distributed with sudo or
https://www.sudo.ws/about/license/ for complete details.
This page is part of the sudo (execute a command as another user)
project. Information about the project can be found at
https://www.sudo.ws/. If you have a bug report for this manual
page, see ⟨https://bugzilla.sudo.ws/⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/sudo-project/sudo⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-08.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Sudo 1.9.16 April 17, 2024 SUDOERS(5)
Pages that refer to this page: proc(5)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|