cron(1M) cron(1M)
NAME [Toc] [Back]
cron - timed-job execution daemon
SYNOPSIS [Toc] [Back]
/usr/sbin/cron
DESCRIPTION [Toc] [Back]
cron executes commands at specified dates and times. Regularly
scheduled commands can be specified according to instructions placed
in crontab files. Users can submit their own crontab files with a
crontab command (see crontab(1)). Users can submit commands that are
to be executed only once with an at or batch command.
Since cron never exits, it should be executed only once. This is best
done by running cron from the initialization process with the startup
script /sbin/init.d/cron (see init(1M)).
cron only establishes a schedule for crontab files and at/batch
command files during process initialization and when it is notified by
at, batch, or crontab that a file has been added, deleted, or
modified.
When cron executes a job, the job's user and group IDs are set to
those of the user who submitted the job.
Spring and Autumn Time Transitions [Toc] [Back]
On the days of daylight savings (summer) time transition (in time
zones and countries where daylight savings time applies), cron
schedules commands differently from normal.
In the following description, an ambiguous time refers to an hour and
minute that occurs twice in the same day because of a daylight savings
time transition (usually on a day during the Autumn season). A
nonexistent time refers to an hour and minute that does not occur
because of a daylight savings time transition (usually on a day during
the Spring season). DST-shift refers to the offset that is applied to
standard time to result in daylight savings time. This is normally
one hour, but can be any combination of hours and minutes up to 23
hours and 59 minutes (see tztab(4)).
When a command is specified to run at an ambiguous time, the command
is executed only once at the first occurrence of the ambiguous time.
When a command is specified to run at a nonexistent time, the command
is executed after the specified time by an amount of time equal to the
DST-shift. When such an adjustment would conflict with another time
specified to run the command, the command is run only once rather than
running the command twice at the same time.
Commands that are scheduled to run during all hours (there is a * is
in the hour field of the crontab entry) are scheduled without any
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cron(1M) cron(1M)
adjustment.
EXTERNAL INFLUENCES [Toc] [Back]
Environment Variables
LANG determines the language in which messages are displayed.
If LANG is not specified or is set to the empty string, it defaults to
"C" (see lang(5)). If any internationalization variable contains an
invalid setting, all internationalization variables default to "C"
(see environ(5)).
DIAGNOSTICS [Toc] [Back]
A history of all actions taken by cron is recorded in
/var/adm/cron/log.
EXAMPLES [Toc] [Back]
The following examples assume that the time zone is MST7MDT. In this
time zone, the DST transition occurs one second before 2:00 a.m. and
the DST-shift is 1 hour.
Consider the following entries in a crontab file:
# Minute Hour MonthDay Month Weekday Command
# ----------------------------------------------------------
0 01 * * * Job_1
0 02 * * * Job_2
0 03 * * * Job_3
0 04 * * * Job_4
0 * * * * Job_hourly
0 2,3,4 * * * Multiple_1
0 2,4 * * * Multiple_2
For the period of 1:00 a.m. to 4:00 a.m. on the days of DST
transition, the results will be:
Job Times Run in Fall Times Run in Spring
____________________________________________________
Job_1 01:00 MDT 01:00 MST
Job_2 02:00 MDT 03:00 MDT
Job_3 03:00 MST 03:00 MDT
Job_4 04:00 MST 04:00 MDT
Job_hourly 01:00 MDT 01:00 MST
02:00 MDT
02:00 MST
03:00 MST 03:00 MDT
04:00 MST 04:00 MDT
Multiple_1 02:00 MDT
03:00 MST 03:00 MDT
04:00 MST 04:00 MDT
Multiple_2 02:00 MDT 03:00 MDT
04:00 MST 04:00 MDT
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WARNINGS [Toc] [Back]
In the Spring, when there is a nonexistent hour because of daylight
savings time, a command that is scheduled to run multiple times during
the nonexistent hour will only be run once. For example, a command
scheduled to run at 2:00 and 2:30 a.m. in the MST7MDT time zone will
only run at 3:00 a.m. The command that was scheduled at 2:30 a.m.
will not be run at all, instead of running at 3:30 a.m.
DEPENDENCIES [Toc] [Back]
HP Process Resource Manager
If the optional HP Process Resource Management (PRM) software is
installed and configured, jobs are launched in the initial process
resource group of the user that scheduled the job. The user's initial
group is determined at the time the job is started, not when the job
is scheduled. If the user's initial group is not defined, the job
runs in the user default group (PRMID=1). See prmconfig(1) for a
description of how to configure HP PRM, and prmconf(4) for a
description of how the user's initial process resource group is
determined.
AUTHOR [Toc] [Back]
cron was developed by AT&T and HP.
FILES [Toc] [Back]
/var/adm/cron Main cron directory
/var/spool/cron/atjobs Directory containing at and batch job
files
/var/spool/cron/crontabs Directory containing crontab files
/var/adm/cron/log Accounting information
SEE ALSO [Toc] [Back]
at(1), crontab(1), sh(1), init(1M), queuedefs(4), tztab(4).
HP Process Resource Manager: prmconfig(1), prmconf(4) in HP Process
Resource Manager User's Guide.
STANDARDS CONFORMANCE [Toc] [Back]
cron: SVID2, SVID3
Hewlett-Packard Company - 3 - HP-UX 11i Version 2: August 2003 [ Back ] |
