Cron on Kenno's Open Note

Replacing cron with systemd timer

Tue, 03 Sep 2024 16:15:58 +1000

Well, I don’t currently really have a good reason to replace a working cron job with systemd-timer beside practicing it.

The following is the existing cron task for www-data user. I want to convert this cron to a systemd-timer:

$ sudo crontab -l -u www-data

# m h  dom mon dow   command
*/5 * * * * php -f /var/www/nextcloud/cron.php

The above output indicates that the command php -f /var/www/nextcloud/cron.php is run at every 5th minute, of course by www-data user.

Crontab Tip

Sun, 13 Dec 2020 23:01:32 +1100

On Fedora based system, whenever I need help writing a cron task and confused which field is minute, hour, day,..etc, I usually check the /etc/crontab file.

❯ cat /etc/crontab 
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# 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

Recently, I found an online cron scheduler editor - crontab.guru. It can be used to create a new task expression, or we can use it to verify the existing cron schedule expressions that we have.

How to test cron

Tue, 18 Feb 2014 14:33:22 +0000

So you drop a script in /etc/cron.daily. How to check if that script does what it is expected to do without having to wait, in this case, a day?

Here is how:

# run-parts -v /etc/cron.daily

Reference:

http://stackoverflow.com/questions/4984725/how-to-test-cron-job

Install crontab on CentOS 6

Mon, 27 May 2013 14:33:26 +0000

When you install CentOS 6 using minimal CD, a lot of packages aren’t installed by default; cron included. To install it,

# yum install cronie

After the installation, you can verify that crond is running:

# chkconfig --list crond
crond 0:off 1:off 2:on 3:on 4:on 5:on 6:off