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 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 com-
       mand 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)