crontab man page on ElementaryOS

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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 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 existance 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
       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  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'
       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 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

       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.

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)
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