*BASH User Commands Ubuntu 10.04.4 LTS Server coreutils
CRONTAB(1)                                                          CRONTAB(1)

       crontab - maintain crontab files for individual users (V3)

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

       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 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.  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 tweaked.  If this option is not given,  crontab  exam-
       ines "your" crontab, i.e., the crontab of the person executing the com-
       mand.  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  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.

       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 vari-
       able CRONTAB_NOHEADER to 'N', which will cause the crontab  -l  command
       to emit the extraneous header.

       crontab(5), cron(8)


       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.

       Although cron requires that each entry in a crontab end  in  a  newline
       character,  neither the crontab command nor the cron daemon will detect
       this error. Instead, the crontab will appear to load normally. However,
       the  command  will  never  run.  The best choice is to ensure that your
       crontab has a blank line at the end.

       Paul Vixie <paul@vix.com>

4th Berkeley Distribution      29 December 1993                     CRONTAB(1)