CRONTAB(1)CRONTAB(1)NAMEcrontab - maintains crontab files for individual users
SYNOPSIScrontab [-u user] file
crontab [-u user] [-l | -r | -e] [-i] [-s]
crontab-n [ hostname ]
crontab-c
DESCRIPTION
Crontab 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(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 to set up users, which are allowed or disal‐
lowed 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 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.
-l Displays the current crontab on standard output.
-r Removes the current crontab.
-e Edits the current crontab using the editor specified by the VIS‐
UAL 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 / replace‐
ment 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 spec‐
ify 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.
SEE ALSOcrontab(5),cron(8)FILES
/etc/cron.allow
/etc/cron.deny
STANDARDS
The crontab 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.
DIAGNOSTICS
An informative usage message appears if you run a crontab with a faulty
command defined in it.
AUTHOR
Paul Vixie <vixie@isc.org>
Colin Dean <colin@colin-dean.org>
22 September 2010 CRONTAB(1)
