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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | MODULE TYPES PROVIDED | RETURN VALUES | EXAMPLES | SEE ALSO | AUTHOR | COLOPHON |
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PAM_UNIX(8) Linux-PAM Manual PAM_UNIX(8)
pam_unix - Module for traditional password authentication
pam_unix.so [...]
This is the standard Unix authentication module. It uses standard
calls from the system's libraries to retrieve and set account
information as well as authentication. Usually this is obtained
from the /etc/passwd and the /etc/shadow file as well if shadow
is enabled.
The account component performs the task of establishing the
status of the user's account and password based on the following
shadow elements: expire, last_change, max_change, min_change,
warn_change. In the case of the latter, it may offer advice to
the user on changing their password or, through the
PAM_AUTHTOKEN_REQD return, delay giving service to the user until
they have established a new password. The entries listed above
are documented in the shadow(5) manual page. Should the user's
record not contain one or more of these entries, the
corresponding shadow check is not performed.
The authentication component performs the task of checking the
users credentials (password). The default action of this module
is to not permit the user access to a service if their official
password is blank.
A helper binary, unix_chkpwd(8), is provided to check the user's
password when it is stored in a read protected database. This
binary is very simple and will only check the password of the
user invoking it. It is called transparently on behalf of the
user by the authenticating component of this module. In this way
it is possible for applications like xlock(1) to work without
being setuid-root. The module, by default, will temporarily turn
off SIGCHLD handling for the duration of execution of the helper
binary. This is generally the right thing to do, as many
applications are not prepared to handle this signal from a child
they didn't know was fork()d. The noreap module argument can be
used to suppress this temporary shielding and may be needed for
use with certain applications.
The maximum length of a password supported by the pam_unix module
via the helper binary is PAM_MAX_RESP_SIZE - currently 512 bytes.
The rest of the password provided by the conversation function to
the module will be ignored.
The password component of this module performs the task of
updating the user's password. The default encryption hash is
taken from the ENCRYPT_METHOD variable from /etc/login.defs
The session component of this module logs when a user logins or
leave the system.
Remaining arguments, supported by others functions of this
module, are silently ignored. Other arguments are logged as
errors through syslog(3).
debug
Turns on debugging via syslog(3).
audit
A little more extreme than debug.
quiet
Turns off informational messages namely messages about
session open and close via syslog(3).
nullok
The default action of this module is to not permit the user
access to a service if their official password is blank. The
nullok argument overrides this default.
nullresetok
Allow users to authenticate with blank password if password
reset is enforced even if nullok is not set. If password
reset is not required and nullok is not set the
authentication with blank password will be denied.
try_first_pass
Before prompting the user for their password, the module
first tries the previous stacked module's password in case
that satisfies this module as well.
use_first_pass
The argument use_first_pass forces the module to use a
previous stacked modules password and will never prompt the
user - if no password is available or the password is not
appropriate, the user will be denied access.
nodelay
This argument can be used to discourage the authentication
component from requesting a delay should the authentication
as a whole fail. The default action is for the module to
request a delay-on-failure of the order of two second.
use_authtok
When password changing enforce the module to set the new
password to the one provided by a previously stacked password
module (this is used in the example of the stacking of the
pam_passwdqc module documented below).
authtok_type=type
This argument can be used to modify the password prompt when
changing passwords to include the type of the password. Empty
by default.
nis
NIS RPC is used for setting new passwords.
remember=n
The last n passwords for each user are saved in
/etc/security/opasswd in order to force password change
history and keep the user from alternating between the same
password too frequently. The MD5 password hash algorithm is
used for storing the old passwords. Instead of this option
the pam_pwhistory module should be used.
shadow
Try to maintain a shadow based system.
md5
When a user changes their password next, encrypt it with the
MD5 algorithm.
bigcrypt
When a user changes their password next, encrypt it with the
DEC C2 algorithm.
sha256
When a user changes their password next, encrypt it with the
SHA256 algorithm. The SHA256 algorithm must be supported by
the crypt(3) function.
sha512
When a user changes their password next, encrypt it with the
SHA512 algorithm. The SHA512 algorithm must be supported by
the crypt(3) function.
blowfish
When a user changes their password next, encrypt it with the
blowfish algorithm. The blowfish algorithm must be supported
by the crypt(3) function.
gost_yescrypt
When a user changes their password next, encrypt it with the
gost-yescrypt algorithm. The gost-yescrypt algorithm must be
supported by the crypt(3) function.
yescrypt
When a user changes their password next, encrypt it with the
yescrypt algorithm. The yescrypt algorithm must be supported
by the crypt(3) function.
rounds=n
Set the optional number of rounds of the SHA256, SHA512,
blowfish, gost-yescrypt, and yescrypt password hashing
algorithms to n.
broken_shadow
Ignore errors reading shadow information for users in the
account management module.
minlen=n
Set a minimum password length of n characters. The max. for
DES crypt based passwords are 8 characters.
no_pass_expiry
When set ignore password expiration as defined by the shadow
entry of the user. The option has an effect only in case
pam_unix was not used for the authentication or it returned
authentication failure meaning that other authentication
source or method succeeded. The example can be public key
authentication in sshd. The module will return PAM_SUCCESS
instead of eventual PAM_NEW_AUTHTOK_REQD or
PAM_AUTHTOK_EXPIRED.
Invalid arguments are logged with syslog(3).
All module types (account, auth, password and session) are
provided.
PAM_IGNORE
Ignore this module.
An example usage for /etc/pam.d/login would be:
# Authenticate the user
auth required pam_unix.so
# Ensure users account and password are still active
account required pam_unix.so
# Change the user's password, but at first check the strength
# with pam_passwdqc(8)
password required pam_passwdqc.so config=/etc/passwdqc.conf
password required pam_unix.so use_authtok nullok yescrypt
session required pam_unix.so
login.defs(5), pam.conf(5), pam.d(5), pam(8)
pam_unix was written by various people.
This page is part of the linux-pam (Pluggable Authentication
Modules for Linux) project. Information about the project can be
found at ⟨http://www.linux-pam.org/⟩. If you have a bug report
for this manual page, see ⟨//www.linux-pam.org/⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/linux-pam/linux-pam.git⟩ on 2023-12-22. (At
that time, the date of the most recent commit that was found in
the repository was 2023-12-18.) 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]
Linux-PAM Manual 12/22/2023 PAM_UNIX(8)
Pages that refer to this page: passwd(5), unix_chkpwd(8), unix_update(8)
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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. |
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