crontab

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
       crontab -V

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 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.

OPTIONS
       -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.

       -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.

CAVEATS
       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.

SEE ALSO
       crontab(5), cron(8)

FILES
       /etc/cron.allow
       /etc/cron.deny

STANDARDS
       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.  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⟩



cronie                            2019-10-29                        CRONTAB(1)