Differences between version 3 and predecessor to the previous major change of crontab(1).
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| Newer page: | version 3 | Last edited on Monday, February 14, 2005 12:15:26 am | by CraigBox | Revert |
| Older page: | version 2 | Last edited on Saturday, February 12, 2005 7:16:33 pm | by DrewStephens | Revert |
@@ -1,130 +1,61 @@
-CRONTAB
-!!!CRONTAB
-NAME
-SYNOPSIS
-DESCRIPTION
-DEBIAN SPECIFIC
-SEE ALSO
-FILES
-STANDARDS
-DIAGNOSTICS
-BUGS
-AUTHOR
-----
!!NAME
+crontab - maintain crontab files for individual users (V3)
-
-crontab - maintain crontab files for individual users (V3)
!!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 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.
-''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
''-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.
-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
.
+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.
-If the
''-u
'' option is given, it specifies
the name of
-user whose crontab is to
be tweaked
. If this option is
-not given
, ''
crontab'' examines
-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
''-e
'' option is used to edit
the current crontab using
the editor specified by the VISUAL or EDITOR environment variables. The specified editor __must__ edit the file in place; any editor that unlinks the file and recreates it cannot
be used
. After you exit from the editor
, the modified
crontab will be installed automatically
.
-
-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. The specified
-editor __must__ edit the file in place; any editor that
-unlinks the file and recreates it cannot be used. After you
-exit from the editor, the modified crontab will be installed
-automatically.
!!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.
-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)
-
-crontab(5), cron(8)
!!FILES
+
+/etc/cron.allow %%%
+/etc/cron.deny %%%
+
-/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.
+
-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.
+
-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, the neither the crontab command nor the cron daemon will detect this error. Instead, the crontab will appear load normally. However, the command will never run. The best choice is to ensure that your crontab has a blank line at the end.
-Although cron requires that each entry in a crontab end in a
-newline character, the neither the crontab command nor the
-cron daemon will detect this error. Instead, the crontab
-will appear 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
+!!AUTHOR
-Paul Vixie
-----
+Paul Vixie <paul@vix.com>
+!!LOCAL NOTES
-I recently had a problem where a computer was running cronjobs at the wrong time, according to system time. I searched around a bit and found that cronjobs are dependent on the hardware clock's time and as such, even though the system time looked right and my crontab was correce, jobs were running at the wrong time. A quick look at the adjtimex and hwclock man pages fixed that --DrewStephens
+I recently had a problem where a computer was running cronjobs at the wrong time, according to system time. I searched around a bit and found that cronjobs are dependent on the hardware clock's time and as such, even though the system time looked right and my crontab was correce, jobs were running at the wrong time. A quick look at the adjtimex and hwclock man pages fixed that -- !
DrewStephens
