Bug 22954

Summary: cron isn't daylight savings-aware
Product: Base System Reporter: seraf <seraf>
Component: binAssignee: freebsd-bugs (Nobody) <bugs>
Status: Closed FIXED    
Severity: Affects Only Me    
Priority: Normal    
Version: Unspecified   
Hardware: Any   
OS: Any   

Description seraf 2000-11-19 07:30:01 UTC 
cron(8) doesn't seem to be aware of time zones like PST8PDT which occasionally shift forward or backward by an hour for American "Daylight Savings."  The result is cron jobs being skipped over, or running twice.  This is a really old problem, IIRC.

Fix: 

Interim solution: Run the affected system in UTC time, or another time zone with an absolute relationship to UTC.
Permanent solution: Make cron use UTC time, or munge cron's understanding of time, or petition the US government to abolish Daylight Savings!
How-To-Repeat: Schedule a cron job which runs within the hour following the pre-shift time of the 1hr-forward-shift (it will never run), or one which runs without the hour preceding the post-shift time of the 1hr-back-shift (it will run twice).  I *think* I have this right.  It's confusing, isn't it?!
Comment 1 Doug Barton freebsd_committer freebsd_triage 2000-11-19 18:04:52 UTC 
State Changed
From-To: open->closed


The problems are actually much more complex than you describe. 
Ultimately, the advice in crontab(5) should be heeded, namely 
don't schedule jobs during that time period.