How do I set up a Cron job?

Question

How do I add Cron jobs in Ubuntu?

Answer 1

Put a shell script in one of these folders: /etc/cron.daily, /etc/cron.hourly, /etc/cron.monthly or /etc/cron.weekly.

If these are not enough for you you can add more specific tasks eg. twice a month or every 5 minutes or... go to the therminal and type:

crontab -e

this will open your personal crontab (cron configuration file), the first line in that file explains it all (don't you think)! In every line you can define one command to run, and the format is quite simple when you get the hang of it. So the structure is:

minute hour day-of-month mounth day-of-week command

For all the numbers you can use lists eg, 5,34,55 in the first field will mean run et 5 past 34 past and 55 past what ever hour is defined.

You can also use intervals, they are defined like this: */20 this example mens every 20th and is in the minutes this will be equivalent to 0,20,40
So to run a command every monday at 5:30 in efternoon will look like this:

30 17 * * 1 /path/to/command

or every 15 minutes

*/15 * * * * /path/to/command

Note that the day-of-week goes from 0-6 where 0 = sunday.

You can read more here.

Answer 2

I can recommend KDE's Task Scheduler (kde-config-cron) . Access it from the System Settings in the Task Scheduler module there.

It manages both personal and system Crontabs and especially the ease of creating the time boundaries surprised me (see the screenshot below). I think this part is really underrated.

Answer 3

If the job you want to run can be run with the same privileges as your user I recommend using a user crontab which you can edit by running EDITOR="gedit" crontab -e(which will used gedit to edit the crontab file) or simply crontab -e(which will use the default editor) in a terminal.

If you want to run something every 10 minutes, for example, you add a line like this

*/10 * * * * /usr/bin/somedirectory/somecommand

and save the file.

You can see the contents of the user crontab with crontab -l.

The most flexible way is to use the system crontab which you can edit by running sudo crontab -e in a terminal. This will allow you to run your commands as root (in case you need that level of privilege) or any other user on the system.

Then if you want to run something every 10 minutes as root, for example, you add a line like this

*/10 * * * * root /usr/bin/somedirectory/somecommand

and save the file.(notice the addition of the user to the line)

You can see the contents of the system crontab file with sudo crontab -l.

More details at: https://help.ubuntu.com/community/CronHowto

Answer 4

If you prefer to do it using a GUI, you can go to the Software Center and install Scheluded tasks. It will provide a powerful GUI to add cron tasks.

Note that if you use this method, tasks by default will be executed as your own user, not as root. This is usually a good thing.