Differences

This shows you the differences between two versions of the page.

--- linux_wiki:schedule_tasks_using_at_and_cron [2016/02/29 21:44]
billdozor [cron]
+++ linux_wiki:schedule_tasks_using_at_and_cron [2019/05/25 23:50]
@@ Line 1: / Line 1: @@
-====== Schedule Tasks Using At And Cron ======
-**General Information**
-About this page/how-to/script.
-----
-==== at ====
-at is good for one-off jobs that don't need to reoccur regularly.
-Install, Enable, Start
-<code bash>
-yum install at
-systemctl enable atd
-systemctl start atd
-</code>
-Example Times (teatime is 4pm)
-<code bash>
-at now +5 minutes
-at now +5 hours
-at 12:00am
-at teatime
-<enter command> <ctrl+d>
-</code>
-Example job
-<code bash>
-at now +5 minutes
-at>logger "System uptime is:$(uptime)"
-at> <ctrl+d>
-</code>
-View jobs
-<code bash>
-atq
-</code>
-Remove job (cancel job)
-<code bash>
-atrm <job#>
-</code>
-----
-==== cron ====
-cron is for scheduling reoccurring jobs/scripts.
-Edit current user's cron
-<code bash>
-crontab -e
-</code>
-System wide
-<code bash>
-/etc/crontab
-# .---------------- 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
-</code>
-More preferred method: Place scripts inside one of the cron.* directories.
-  * /etc/cron.d/ = system executed jobs (format => /etc/crontab)
-  * /etc/cron.daily/ = daily executed scripts (format => bash script)
-  * /etc/cron.hourly/ = hourly executed scripts (format => bash script)
-  * /etc/cron.monthly/ = monthly executed scripts (format => bash script)
-  * /etc/cron.weekly/ = weekly executed scripts (format => bash script)
-Example custom script in /etc/cron.d
-<code bash>
-*/5 * * * * root /home/user/uptimelog
-</code>
-  * Executes /home/user/uptimelog as root, every 5 mins
-----
-==== Anacron ====
-Anacron runs all scripts in cron.* directories. This allows jobs to be run if the scheduled time was while a system was powered off.
-Main config and contents: /etc/anacrontab
-<code bash>
-#period in days   delay in minutes   job-identifier   command
-	5	cron.daily		nice run-parts /etc/cron.daily
-	25	cron.weekly		nice run-parts /etc/cron.weekly
-@monthly 45	cron.monthly		nice run-parts /etc/cron.monthly
-</code>
-Run all anacron jobs(in /etc/anacrontab), ignore timestamps (note that the "delay in minutes" setting is still in effect)
-<code bash>
-anacron -f
-</code>
-View timestamps for anacron jobs (cron.daily in this example)
-<code bash>
-cat /var/spool/anacron/cron.daily
-</code>
-Run all jobs now, ignore delay specifications in /etc/anacrontab
-<code bash>
-anacron -n
-</code>
-----