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AIX and DST
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cron(1M) cron(1M) NAME
cron - timed-job execution daemon SYNOPSIS
DESCRIPTION
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 com- mands 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 sav- ings 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 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 ALSO
at(1), crontab(1), sh(1), init(1M), queuedefs(4), tztab(4). HP Process Resource Manager: prmconfig(1), prmconf(4) in STANDARDS CONFORMANCE
cron(1M)
