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CRONTAB(1)                             General Commands Manual                            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 or‐
       der 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 existence of any of these files, the root administrative user is always al‐
       lowed 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  op‐
       tion for safety's sake.

       The first form of this command is used to install a new crontab from some named file or stan‐
       dard 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 de‐
       fault 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  prob‐
       lem 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  extra‐
       neous header.

SEE ALSO
       crontab(5), cron(8)

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

       The  files  /etc/cron.allow and /etc/cron.deny if, they exist, must be either world-readable,
       or readable by group ``crontab''. If they are not, then cron will deny access  to  all  users
       until the permissions are fixed.

       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 cor‐
       rect 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 spe‐
       cific 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.

       The files under /var/spool/cron/crontabs are named based on the user's account name.  Crontab
       jobs will not be run for users whose accounts have been renamed either due to changes in  the
       local  system  or  because  they are managed through a central user database (external to the
       system, for example an LDAP directory).



AUTHOR
       Paul Vixie <paul AT 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.



4th Berkeley Distribution                   19 April 2010                                 CRONTAB(1)