I run a cronjob at 2:30AM every day that uses dirvish (a perl wrapper around rsync) to perform backups of several computers. In the fall, at 2AM the clock is rolled back to 1AM. The cronjob runs at 2:30AM, which is 25 hours after the previous day's run. That's not a problem. However, in the spring, at 2AM the clock jumps to 3AM. Vixie cron seems to be smart enough to run all the cron jobs that were scheduled between 2M and 3AM at that point. However, dirvish is started but exits without running the backups! After some troubleshooting I concluded that dirvish does not make the backups because the previous day's run happened less that 24 hours ago (because that day was shortened by the change to DST) so it sees no need to run a backup yet. This problem would persist even if I moved the cronjob to a different time because it has to do with the day having only 23 hours. I solved this by adding a second entry to the crontab that runs at 3:45AM only on the 2nd Sunday in March.