On Sun, 4 Nov 2012 08:58:54 -0500 Michael George <geo...@mutualdata.com> wrote:
> Last night was our change from EDT to EST. So we went through the > 1am-2am hour twice. My crontab has the following: > > # for vixie cron > # $Header: > # /var/cvsroot/gentoo-x86/sys-process/vixie-cron/files/crontab-3.0.1-r4,v > # 1.3 2011/09/20 15:13:51 idl0r Exp $ > > # Global variables > SHELL=/bin/bash > PATH=/sbin:/bin:/usr/sbin:/usr/bin > MAILTO=root > HOME=/ > > # check scripts in cron.hourly, cron.daily, cron.weekly and > cron.monthly 59 * * * * root rm > -f /var/spool/cron/lastrun/cron.hourly 9 3 * * * root rm > -f /var/spool/cron/lastrun/cron.daily 19 4 * * 6 root rm > -f /var/spool/cron/lastrun/cron.weekly 29 5 1 * * root rm > -f /var/spool/cron/lastrun/cron.monthly */10 * * * * root test > -x /usr/sbin/run-crons && /usr/sbin/run-crons > > So the cron.daily file should be removed at 3:09am -- it should only > run once as the 2am-forward time only occurred once. > > However, this morning I have two sets of email from my daily jobs > running. At this time: > > Date: Sun, 4 Nov 2012 02:20:05 -0500 (EST) > > and this time: > > Date: Sun, 4 Nov 2012 03:10:04 -0500 (EST) > > Why would it have run twice? This is clearly documented in the man pages for Vixie cron. cron is utterly unaware of the vagaries and stupidities that humans get up to recording the passage of time. If your crontab is this: 0 0 * * * <something> then when the clock says it is 0 minutes past the 0 hour, the cron will run. That time happened twice. Therefore the cron ran twice. You can't really blame cron for not picking up that an event that is guaranteed to happen once in a period actually happened twice in a period. There comes a time when a developer has to step back and say "To hell with that, it's out of contract spec and actually not my problem!" There are other crons that avoid this problem by taking a completely different approach. You configure them by declaring you want a job to run in a given period of time. When daylight saving kicks in, it sees a job has already run and doesn't do it again. But you have to lose the ability to specify the exact time a job must run at to do it this way. -- Alan McKinnon alan.mckin...@gmail.com
