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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CAVEATS | SEE ALSO | FILES | STANDARDS | DIAGNOSTICS | AUTHOR | COLOPHON |
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CRONTAB(1) User Commands CRONTAB(1)
crontab - maintains crontab files for individual users
crontab [-u user] <file | ->
crontab [-T] <file | ->
crontab [-u user] <-l | -r | -e> [-i] [-s]
crontab -n [ hostname ]
crontab -c
crontab -V
Crontab is the program used to install a crontab table file,
remove or list the existing tables used to serve the cron(8)
daemon. Each user can have their own crontab, and though these
are files in /var/spool/, they are not intended to be edited
directly. For SELinux in MLS mode, you can define more crontabs
for each range. For more information, see selinux(8).
In this version of Cron it is possible to use a network-mounted
shared /var/spool/cron across a cluster of hosts and specify that
only one of the hosts should run the crontab jobs in the
particular directory at any one time. You may also use crontab
from any of these hosts to edit the same shared set of crontab
files, and to set and query which host should run the crontab
jobs.
Scheduling cron jobs with crontab can be allowed or disallowed
for different users. For this purpose, use the cron.allow and
cron.deny files. If the cron.allow file exists, a user must be
listed in it to be allowed to use crontab. If the cron.allow
file does not exist but the cron.deny file does exist, then a
user must not be listed in the cron.deny file in order to use
crontab. If neither of these files exist, then only the super
user is allowed to use crontab.
Another way to restrict the scheduling of cron jobs beyond
crontab is to use PAM authentication in /etc/security/access.conf
to set up users, which are allowed or disallowed to use crontab
or modify system cron jobs in the /etc/cron.d/ directory.
The temporary directory can be set in an environment variable.
If it is not set by the user, the /tmp directory is used.
When listing a crontab on a terminal the output will be colorized
unless an environment variable NO_COLOR is set.
On edition or deletion of the crontab, a backup of the last
crontab will be saved to $XDG_CACHE_HOME/crontab/crontab.bak or
$XDG_CACHE_HOME/crontab/crontab.<user>.bak if -u is used. If the
XDG_CACHE_HOME environment variable is not set, $HOME/.cache will
be used instead.
-u Specifies the name of the user whose crontab is to be
modified. If this option is not used, crontab examines
"your" crontab, i.e., the crontab of the person executing
the command. If no crontab exists for a particular user,
it is created for them the first time the crontab -u
command is used under their username.
-T Test the crontab file syntax without installing it. Once
an issue is found, the validation is interrupted, so this
will not return all the existing issues at the same
execution.
-l Displays the current crontab on standard output.
-r Removes the current crontab.
-e Edits the current crontab using the editor specified by
the VISUAL or EDITOR environment variables. After you
exit from the editor, the modified crontab will be
installed automatically.
-i This option modifies the -r option to prompt the user for
a 'y/Y' response before actually removing the crontab.
-s Appends the current SELinux security context string as an
MLS_LEVEL setting to the crontab file before editing /
replacement occurs - see the documentation of MLS_LEVEL in
crontab(5).
-n This option is relevant only if cron(8) was started with
the -c option, to enable clustering support. It is used
to set the host in the cluster which should run the jobs
specified in the crontab files in the /var/spool/cron
directory. If a hostname is supplied, the host whose
hostname returned by gethostname(2) matches the supplied
hostname, will be selected to run the selected cron jobs
subsequently. If there is no host in the cluster matching
the supplied hostname, or you explicitly specify an empty
hostname, then the selected jobs will not be run at all.
If the hostname is omitted, the name of the local host
returned by gethostname(2) is used. Using this option has
no effect on the /etc/crontab file and the files in the
/etc/cron.d directory, which are always run, and
considered host-specific. For more information on
clustering support, see cron(8).
-c This option is only relevant if cron(8) was started with
the -c option, to enable clustering support. It is used
to query which host in the cluster is currently set to run
the jobs specified in the crontab files in the directory
/var/spool/cron , as set using the -n option.
-V Print version and exit.
The files cron.allow and cron.deny cannot be used to restrict the
execution of cron jobs; they only restrict the use of crontab.
In particular, restricting access to crontab has no effect on an
existing crontab of a user. Its jobs will continue to be executed
until the crontab is removed.
The files cron.allow and cron.deny must be readable by the user
invoking crontab. If this is not the case, then they are treated
as non-existent.
crontab(5), cron(8)
/etc/cron.allow
/etc/cron.deny
The crontab command conforms to IEEE Std1003.2-1992 (``POSIX'')
with one exception: For replacing the current crontab with data
from standard input the - has to be specified on the command line
if the standard input is a TTY. This new command syntax differs
from previous versions of Vixie Cron, as well as from the classic
SVR3 syntax.
An informative usage message appears if you run a crontab with a
faulty command defined in it.
Paul Vixie ⟨[email protected]⟩
Colin Dean ⟨[email protected]⟩
This page is part of the cronie (crond daemon) project.
Information about the project can be found at
⟨https://github.com/cronie-crond/cronie⟩. If you have a bug
report for this manual page, see
⟨https://github.com/cronie-crond/cronie/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/cronie-crond/cronie.git⟩ on 2024-06-14. (At
that time, the date of the most recent commit that was found in
the repository was 2024-05-31.) 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]
cronie 2019-10-29 CRONTAB(1)
Pages that refer to this page: cronnext(1), pmsnap(1), anacrontab(5), crontab(5), systemd.exec(5), cron(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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