HP-UX Reference (11i v2 03/08) - 1M System Administration Commands A-M (vol 3)

c
cron(1M) cron(1M)
NAME
cron - timed-job execution daemon
SYNOPSIS
/usr/sbin/cron
DESCRIPTION
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
cron-
tab 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 ini-
tialization 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 initializa-
tion and when it is notified by
at, batch,orcrontab 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
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 adjustment.
EXTERNAL INFLUENCES
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 internationali-
zation variable contains an invalid setting, all internationalization variables default to "C" (see
environ(5)).
DIAGNOSTICS
A history of all actions taken by
cron is recorded in /var/adm/cron/log.
EXAMPLES
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
Section 1M−−110 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: August 2003