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       crontab - maintain crontab files for individual users (Vixie Cron)


       crontab [ -u user ] file
       crontab [ -u user ] [ -i ] { -e | -l | -r }


       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

       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.


       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

       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.


       crontab(5), cron(8)



       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


       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.


       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


       Paul Vixie <>