Source: LinuxFoundationX: LFS101x.2 Introduction to Linux
cron
cron is a time-based scheduling utility program. It can launch routine background jobs at specific times and/or days on an on-going basis. cron is driven by a configuration file called /etc/crontab (cron table) which contains the various shell commands that need to be run at the properly scheduled times. There are both system-wide crontab files and individual user-based ones. Each line of a crontab file represents a job, and is composed of a so-called CRON expression, followed by a shell command to execute.
The crontab -e command will open the crontab editor to edit existing jobs or to create new jobs. Each line of the crontab file will contain 6 fields:
Field Description Values
MIN Minutes 0 to 59
HOUR Hour field 0 to 23
DOM Day of Month 1-31
MON Month field 1-12
DOW Day Of Week 0-6 (0 = Sunday)
CMD Command Any command to be executed
Examples:
-
The entry
* * * * * /usr/local/bin/execute/this/script.shwill schedule a job to execute ‘script.sh’ every minute of every hour of every day of the month, and every month and every day in the week. -
The entry
30 08 10 06 * /home/sysadmin/full-backupwill schedule a full-backup at 8.30am, 10-June irrespective of the day of the week.
Delayed jobs
Sources:
https://github.com/collectiveidea/delayed_job
http://www.sitepoint.com/delayed-jobs-best-practices/
http://www.sitepoint.com/new-rails-shiny-activejob/
http://www.sitepoint.com/dont-get-activejob/
http://blog.andolasoft.com/2013/04/4-simple-steps-to-implement-delayed-job-in-rails.html