crontab(1) - phpMan

CRONTAB(1) User Commands CRONTAB(1)

NAME
crontab - maintains crontab files for individual users

SYNOPSIS
crontab [-u user] file
crontab [-u user] [-l | -r | -e] [-i] [-s]
crontab -n [ hostname ]
crontab -c

DESCRIPTION
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(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 and cron.deny files. If the cron.allow 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 in /etc/secu-
rity/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.

OPTIONS
-u 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 execut-
ing the command. Note that su(8) may confuse crontab, thus, when executing com-
mands 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.

-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 envi-
ronment 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 host-
name 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.