cron on Centos

华风

1. crond.service
2. configuration
2.0 format
　　
# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * user-name command to be executed
2.1 per-user
　　/var/spool/cron/<user_name>
2.2 system-level
　　/etc/crontab
/etc/cron.d/
2.3 configure to run all script in a folder
　　First, create a folder and put all script into it

And then, use "run-parts",
to create a configure item in one of cron configuraiton files, like this:

01 * * * * root run-parts /etc/cron.hourly
3. How to configure a cron job
3.1 directly add conf item into
　　
/var/spool/cron/<user_name>
/etc/crontab
3.2 create a cron conf file and put it into
　　/etc/cron.d/
3.3 use crontab
　　crontab: invalid option -- 'h'
crontab: usage error: unrecognized option
Usage:
crontab [options] file
crontab [options]
crontab -n [hostname]

Options:
-u <user> define user
-e edit user's crontab
-l list user's crontab
-r delete user's crontab
-i prompt before deleting
-n <host> set host in cluster to run users' crontabs
-c get host in cluster to run users' crontabs
-s selinux context
-x <mask> enable debugging
4. cron log
　　/var/log/cron
5. anacron
　　asynchrous cron
5.1 cron trigger anacron:
　　/etc/cron.hourly/0anacron
5.2 anacron configuraiton
　　/etc/anacrontab
　　
1 5 cron.daily nice run-parts /etc/cron.daily
7 25 cron.weekly nice run-parts /etc/cron.weekly
@monthly 45 cron.monthly nice run-parts /etc/cron.monthly
　　
/etc/cron.d/0hourly ==> anacron ==> /etc/anacrontab/ ==> cron ==> /etc/cron.daily/cron.weekly/cron.monthly