Red Hat Bugzilla – Bug 1986
cron skips jobs on first day of DST
Last modified: 2008-05-01 11:37:49 EDT
Because the clock doesn't pass through the times 2:00-2:59 on the first day of daylight savings time, jobs (such as my daily backups!) that are scheduled to begin anytime in this one hour window are skipped. Arguably this is correct in the sense that these times don't exist, but if this behavior is to be considerd "normal", then the man page should warn users about this.
Your suggestion has been passed on to a developer for further review.
I have reviewed the Single Unix Specification definition of crontab (it doesn't talk about cron specifically, but the crontab definition talks about the crontab format as well) and there is no indication that cron should magically re-schedule jobs that are scheduled for a non-existant time. Indeed, it is not clear what the right thing to do would be if cron tried to shuffle the schedules. I have reclassified this bug report as a documentation bug report and we'll change the man page to explicitly mention that cron will not run jobs during times that do not exist, such as during daylight savings time conversions.
Man page updated with this information in vixie-cron-3.0.1-32
Following up on this, in RedHat 7.3, the cron manpage makes no mention of daylight saving time. It is not clear whether some jobs may be run twice or not at all.