DJE Systems
OpenVMS Mentoring

In VMSland, there is no "cron"-like daemon that ships with VMS.

There have been some third-party products to do this kind of job scheduling. However, they do not attempt to emulate cron and, unlike cron, they usually include some provision for interdependencies between jobs such that if a key job in a sequence of jobs should fail, the subsequent jobs in the chain will not run without manual intervention.

The SUBMIT command functions most like the UN*X-land "at" command. The /AFTER qualifier can be used to specify the date/time after which the job should run.

Any DCL procedure set up to run as a batch job can reSUBMIT itself for a date/time in the future by determining it's own identity (See HELP Lexicals F$ENVIRONMENT and the PROCEDURE keyword under that function) and either using a hard-coded "delta" time expression or by actually calculating a future date based on days of the month, week, year, etc.

"Delta" time expressions indicate either a displacement forward into the future, such as "+1-03:00:00", that is "plus one day, three hours" or a fixed time of day and a displacement, such as "03:00:00+1-", that is "03:00:00 (03:00 a.m. system time) plus one day".

Absolute time expressions can also be used. This is usually used when the procedure calculates the next run date, then uses that value for the /AFTER qualifier. For example, if a procedure calculates that it should run next at 03:00:00 on 15-Jan-2003, then the value "15-JAN-2003 03:00:00" could be assigned to a symbol, for example, NEXT_RUN and that symbol could be used to specify the value for the /AFTER qualifier: /AFTER="''NEXT_RUN'" or /AFTER=&NEXT_RUN.

Some cron-like DCL procedures have been developed by various people in the VMS user community. They can be found by searching the Google Groups archive of the comp.os.vms newsgroup with the keyword "cron".

Return to DJE Systems OpenVMS support Page

Tradenames, trademarks, service marks, etc. appearing on this page are the property of their registered owners.

"DJE Systems" is a service mark of David J. Dachtera, doing business as DJE Systems.

This page Copyright ©1998-2004 by David J. Dachtera, All Rights Reserved.