21.6 Clusterwide cron


21.6 Clusterwide cron

One area of cluster confusion involves the cron (8) daemon. The crontab files for each member (found in /var/spool/cron/crontabs) are member-specific – /var/spool/cron is a CDSL.

 # fln /var/spool/cron /var/spool/cron -> ../cluster/members/{memb}/spool/cron 

Not only are the crontab files member-specific, but the cron daemon is also not cluster-aware.

 # clu_ps | grep -E "^member|^=|^-|cron" | grep -v grep ================================================================================ member1   (molari)             ps -ef -------------------------------------------------------------------------------- root      525300 524289     0.0 13:47:26 ??         0:00.02 /usr/sbin/cron ================================================================================ member2   (sheridan)           ps -ef -------------------------------------------------------------------------------- root      1049553 1048577   0.0 13:47:25 ??         0:00.01 /usr/sbin/cron ================================================================================ 

This means that on each member, cron acts independently from all the other members, and that a cron job to backup a data directory would run on the same file systems at the same times on all members in the cluster. Obviously not a good arrangement!

This problem is solved in one of the Best Practices documents that can be found on HP's Best Practices website:

http://www.tru64unix.compaq.com/docs/best_practices/clus_bps.html

This Best Practices document shows you how to set up a CAA service to handle cron jobs that need to be addressed in a cluster-aware fashion.

For more on setting up CAA, refer to Chapter 23 and Chapter 24.




TruCluster Server Handbook
TruCluster Server Handbook (HP Technologies)
ISBN: 1555582591
EAN: 2147483647
Year: 2005
Pages: 273

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