cron(1m)
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cron
clock agent
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SYNTAX
/etc/cron
DESCRIPTION
Cron executes commands at specified dates and times. You can
schedule commands on a regular basis according to instructions
found in crontab files.
NOTE:
You must have permissions to create crontab files.
Commands that are to be executed only once may be submitted via
the at command. Because cron never exits, it should be executed
only once. This is best done by running cron from the
initialization process through the rc script mechanism. (see
rc.init(1m)).
You can change the way cron schedules jobs by changing entries in
the queuedefs file. The file has two lines, one for the at queue
(a.) and one for the batch queue (b.):
a.XjYnZw
b.XjYnZw
where
X is the maximum number of jobs allowed to execute
simultaneously. This cannot be set higher than 25.
Y is the nice factor--the job priority number will be raised
by this amount. The higher the number, the less attention
the job gets from the CPU. The maximum nice factor is 20.
Z is how long to wait, in seconds, before trying to reschedule
a queue request when the job queue is full.
The default limits are set to work as follows:
a.4j1n
b.2j2n90w
If you increase the job limits, be on guard for a potential
DG/UX 4.00 Page 1
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cron(1m)
impact on system performance, especially on smaller machines or
machines having lots of active users.
FILES
/usr/lib/cron main cron directory
/usr/lib/cron/log accounting information
/usr/lib/cron/queuedefs
scheduling information
/usr/spool/cron spool area
/usr/bin/crontab cron instruction file
NOTES
Cron(1m) examines crontab files (located in /usr/spool/cron) and
at command files only during process initialization and when a
file changes. This reduces the overhead of checking for new or
changed files. You can submit your own crontab file via the
crontab command.
SEE ALSO
at(1), crontab(1), init(1m), sh(1).
DIAGNOSTICS
A history of all actions taken by cron are recorded in
/usr/lib/cron/log.
BUGS
When it runs out of jobs to do, cron(1m) tries to redo jobs it
has already done. This behavior is potentially dangerous, so you
should always keep it busy, preferably with something like
uuclean or a dummy job. This bug originated in AT&T System V.
DG/UX 4.00 Page 2
Licensed material--property of copyright holder(s)