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