crontab

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 order
       to use this command.

       If neither of these files exists, then depending on site-dependent con-
       figuration  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 administra-
       tive  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 con-
       fuse crontab and that if you are running inside of su(8) you should al-
       ways 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  automati-
       cally.   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' re-
       sponse 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 se-
       quence

       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 vari-
       able 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

       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 syntacti-
       cally correct crontabs will be written there.  This is enforced by hav-
       ing  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  con-
       sider 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  sys-
       tem, for example an LDAP directory).

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.

4th Berkeley Distribution        19 April 2010                      CRONTAB(1)