by Ras
26. April 2012 21:49
### system scheduler -cron ##
1- permits recurring execution of tasks/scripts
2- permits one-time execution of tasks via 'at' command
3- logs results of executed tasks
4- restrictions/permissions via cron.deny, cron.allow,at.*
location: /var/spool/cron
/var/spool/cron/crontabs - recurring jobs - %username% folder for each user
/var/spool/cron/atjobs - one-time jobs
crontab columns:
m(0-59) h(0-23) dom(1-31) m(1-12) dow(0-6) command
examples
10 3 * * * - every day at 3:10
* * * * * - every minute
*/5 * * * * - every 5 min
1 0-4 * * * * - 1 minute after hours 0-4
0 0,2,4,6 * * * - top of the hours 0,2,4,6
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