On Thursday 11 March 2010 12:50:13 Timothy Murphy wrote:
Is one meant to have one or the other? If so, which is recommended? I have
[tim@helen etc]$ cat anacrontab # /etc/anacrontab: configuration file for anacron
# See anacron(8) and anacrontab(5) for details.
SHELL=/bin/sh PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root
1 65 cron.daily run-parts /etc/cron.daily 7 70 cron.weekly run-parts /etc/cron.weekly 30 75 cron.monthly run-parts /etc/cron.monthly
[tim@helen etc]$ cat crontab SHELL=/bin/bash PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root HOME=/
# run-parts 01 * * * * root run-parts /etc/cron.hourly 02 4 * * * root run-parts /etc/cron.daily 22 4 * * 0 root run-parts /etc/cron.weekly 42 4 1 * * root run-parts /etc/cron.monthly
I didn't write either of these, they must have been automatically installed.
My impression is that anacrontab was ignored until recently, but now as far as I can see both are being read and acted on.
Any enlightenment gratefully received.
Both are typically installed as part of a CentOS install. But you only need one or the other. Generally cron on a 24x7 machine and anacron on a laptop. One or the otrher is mormally disabled.
cron is a fixed time schedular. I wakes up every minute and checks if there are any jobs to be run. It checks /etc'/crontab for system crons to run and also in /var/spool/cron for individual crons to be run.
e.g from my /etc/crontab file
22 4 * * 0 root run-parts /etc/cron.weekly
says
At 22 minutes past 4am run /etc/cron.weekly
anacron is for machines that are not up 24x7 so they could miss some of the times when "cron jobs" were to be run. So anacron wakes up and checks the /etc/anacrontab file. Then it runs any jobs after a certain delay period ( not at a fixed time )
e.g from my /etc/anacrontab file
7 20 cron.weekly nice run-parts /etc/cron.weekly
says
20 minutes after waking up every 7 days run /etc/cron.weekly
Hope this helps,
Tony