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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  configuration  parame-
       ters,  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  actu-
       ally 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>

4th Berkeley Distribution		  19 April 2010 			       CRONTAB(1)
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