cron(1M)cron(1M)NAMEcron - timed-job execution daemon
SYNOPSISDESCRIPTION
executes commands at specified dates and times. Regularly scheduled
commands can be specified according to instructions placed in files.
Users can submit their own files with a command (see crontab(1)).
Users can submit commands that are to be executed only once with an or
command.
Since never exits, it should be executed only once. This is best done
by running from the initialization process with the startup script (see
init(1M)).
only establishes a schedule for files and or command files during
process initialization and when it is notified by or that a file has
been added, deleted, or modified.
When 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), 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 nonex‐
istent 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 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 entry) are scheduled without any adjustment.
EXTERNAL INFLUENCES
Environment Variables
determines the language in which messages are displayed.
If 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
A history of all actions taken by is recorded in
EXAMPLES
The following examples assume that the time zone is 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 file:
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
WARNINGS
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 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
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 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
was developed by AT&T and HP.
FILES
Main directory
Directory containing and job files
Directory containing files
Accounting information
SEE ALSOat(1), crontab(1), sh(1), init(1M), queuedefs(4), tztab(4).
HP Process Resource Manager: prmconfig(1), prmconf(4) in
STANDARDS CONFORMANCEcron(1M)
