CRONTAB(1)                                                                                                                        CRONTAB(1)
NAME
       crontab - maintain crontab files for individual users (V3)
SYNOPSIS
       crontab [ -u user ] file
       crontab [ -u user ] { -l | -r [ -i ] | -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  configuration  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
       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
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.
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 <paul@vix.com>
4th Berkeley Distribution                                     29 December 1993                                                    CRONTAB(1)