The cron command starts a process that
executes commands at specified dates and times.
Regularly scheduled commands can be specified according
to instructions found in crontab files in the directory
Users can submit their own crontab file
via the crontab command.
Commands to be executed only once may be
submitted via the at command.
cron normally forks itself and places itself into the background.
When the nofork option is specified, this initial fork is not
This would allow cron to be started via inittab rather
than during system boot time.
The commands are not executed if, at the time of execution,
the requesting user ID or level ID
has been deleted, or if the level is no longer a valid login level for the
cron only examines crontab files and at
command files during process initialization and when a file changes via
the crontab or at commands.
This reduces the overhead of checking for new or
changed files at regularly scheduled intervals.
Because cron never exits, it should be executed only once,
normally through /etc/rc2.d/S75cron at system boot time.
The file /etc/cron.d/LCK_CRON is used as a lock
file to prevent
the execution of more than one
Use the following files, described in
to control cron:
The variable MAXRUN in /etc/default/cron defines the number
of concurrent cron jobs that are allowed to run.
The default is 25.
To specify whether cron is to log all actions,
set CRONLOG to YES
or to NO in /etc/default/cron.
cron usually creates huge log files.
Specify the number of concurrent jobs per user, their priority,
and a retry interval in the file /etc/cron.d/queuedefs.
main cron directory
concurrency, priority, retry options file
log options file
language-specific message file (see LANG in
A history of all actions taken by cron is recorded in
/var/cron/log if logging is turned on.
Changing the time of day clock on the system affects the
execution of jobs specified in crontab files.
If the clock is moved ahead, the jobs scheduled for the skipped time interval
will not be run.
If the clock is moved back, the jobs
already executed in the time interval to be revisited will
be run a second time.
Adjusting the system time because of standard or
alternate time zone changes, including daylight time changes, causes
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004