Crontab Manual

                                   Crontab Manual
SYNOPSIS
     crontab [ -u user ] file
     crontab [ -u user ] { -l | -r | -e }

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 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
     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.

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
     well as from the classic SVR3 syntax.


DIAGNOSTICS
     A fairly informative usage message appears if you run  it  with  a  bad
     command line.


BUGS
     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.


AUTHOR
     Paul Vixie 



4th Berkeley Distribution      29 December 1993                     CRONTAB(1)