CRONTAB(1)                                                                                                                          CRONTAB(1)

NAME

       crontab - maintain crontab files for individual users (Vixie Cron)

SYNOPSIS

       crontab [ -u user ] file
       crontab [ -u user ] [ -i ] { -e | -l | -r }

DESCRIPTION

       crontab  is  the  program  used to install, deinstall or list the tables used to drive the cron(8) daemon in Vixie Cron.  Each user can
       have their own crontab, and though these are files in /var/spool/cron/crontabs, they are not intended to be edited directly.

       If the /etc/cron.allow file exists, then you must be listed (one user per line) therein in order to be allowed to use this command.  If
       the  /etc/cron.allow file does not exist but the /etc/cron.deny file does exist, then you must not be listed in the /etc/cron.deny file
       in order to use this command.

       If neither of these files exists, then depending on site-dependent configuration parameters, only the super user will be allowed to use
       this command, or all users will be able to use this command.

       If  both  files  exist  then  /etc/cron.allow takes precedence. Which means that /etc/cron.deny is not considered and your user must be
       listed in /etc/cron.allow in order to be able to use the crontab.

       Regardless of the existance of any of these files, the root administrative user is always allowed to setup  a  crontab.   For  standard
       Debian systems, all users may use this command.

       If  the -u option is given, it specifies the name of the user whose crontab is to be used (when listing) or modified (when editing). If
       this option is not given, crontab examines "your" crontab, i.e., the crontab of the person executing the command.  Note that su(8)  can
       confuse crontab and that if you are running inside of su(8) you should always use the -u option for safety's sake.

       The  first form of this command is used to install a new crontab from some named file or standard input if the pseudo-filename ``-'' is
       given.

       The -l option causes the current crontab to be displayed on standard output. See the note under DEBIAN SPECIFIC below.

       The -r option causes the current crontab to be removed.

       The -e option is used to edit 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. If neither of the environment variables is defined, then
       the default editor /usr/bin/editor is used.

       The -i option modifies the -r option to prompt the user for a 'y/Y' response before actually removing the crontab.

DEBIAN SPECIFIC

       The "out-of-the-box" behaviour for crontab -l is to display the three line "DO NOT EDIT  THIS  FILE"  header  that  is  placed  at  the
       beginning of the crontab when it is installed. The problem is that it makes the sequence

       crontab -l | crontab -

       non-idempotent  --  you  keep  adding  copies of the header. This causes pain to scripts that use sed to edit a crontab. Therefore, the
       default behaviour of the -l option has been changed to not output such header. You may obtain the original  behaviour  by  setting  the
       environment variable CRONTAB_NOHEADER to 'N', which will cause the crontab -l command to emit the extraneous header.

SEE ALSO

       crontab(5), cron(8)

FILES

       /etc/cron.allow
       /etc/cron.deny
       /var/spool/cron/crontabs

       There  is  one file for each user's crontab under the /var/spool/cron/crontabs directory. Users are not allowed to edit the files under
       that directory directly to ensure that only users allowed by the system to run periodic tasks can  add  them,  and  only  syntactically
       correct  crontabs  will  be written there.  This is enforced by having the directory writable only by the crontab group and configuring
       crontab command with the setgid bid set for that specific group.

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

       A fairly informative usage message appears if you run it with a bad command line.

       cron requires that each entry in a crontab end in a newline character. If the last entry in a crontab is missing the newline, cron will
       consider the crontab (at least partially) broken and refuse to install it.

AUTHOR

       Paul Vixie <paul@vix.com>  is the author of
       cron
       and original creator of this manual page. This page has also been modified for
       Debian by Steve Greenland, Javier Fernandez-Sanguino and Christian Kastner.
 

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