crontab - maintains crontab files for individual users
crontab -n [ hostname
is the program used to install, remove or list the 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
In this version of Cron
it is possible to use a network-mounted shared
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(1)
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.
Running cron jobs can be allowed or disallowed for different users. For this
purpose, use the cron.allow
files. If the
file exists, a user must be listed in it to be allowed to
use cron 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 cron. If neither of these files exists, only the super
user is allowed to use cron. Another way to restrict access to cron is to use
PAM authentication to set up users, which are allowed or disallowed to use
or modify system cron jobs in the /etc/cron.d/
The temporary directory can be set using the environment variable $TMPDIR. If it
is not set by the user, the /tmp
directory is used.
- Appends 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. Note that
su(8) may confuse crontab, thus, when executing commands
under su(8) you should always use the -u option. If no
crontab exists for a particular user, it is created for him the first time
the crontab -u command is used under his username.
- Displays the current crontab on standard output.
- Removes the current crontab.
- 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.
- This option modifies the -r option to prompt the user for a 'y/Y'
response before actually removing the crontab.
- 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).
- 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).
- 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
command conforms to IEEE Std1003.2-1992 (``POSIX''). 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 <firstname.lastname@example.org>
Colin Dean <email@example.com>