CRONTAB

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 con‐
figuration  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 administra‐
tive  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 con‐
fuse 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.

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 vari‐
able 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  syntacti‐
cally correct crontabs will be written there.  This is enforced by hav‐
ing the directory writable only by the crontab  group  and  configuring
crontab command 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 con‐
sider the crontab (at least partially) broken and refuse to install it.

AUTHOR
Paul Vixie <[email protected]> is the author of cron and original creator of
this  manual page. This page has also been modified for Debian by Steve
Greenland, Javier Fernandez-Sanguino and Christian Kastner.

4th Berkeley Distribution        19 April 2010                      CRONTAB(1)
Manual page crontab(1) line 58/108 (END) (press h for help or q to quit)

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