2019-03-18 00:00:00

How can I run a bash script every N seconds?

This is a quick and simple HowTo guide that’ll help you run a bash script every N seconds. Note that you can run root commands from the script as we’ll use systemd.

Create a service that’ll run your script

The first step is to setup a job that’ll execute the script whenever the timer will ask so. You can use nano to make a new service called name.service in /etc/systemd/system/, where you can choose name. If the package is not installed, run the following command and you may continue.

Ubuntu :

sudo apt-get install nano

CentOS / RHEL / CloudLinux / Fedora :

sudo yum install nano

Run nano to create the file:

sudo nano /etc/systemd/system/name.service

and fill it with (ctrl+shift+v to paste in terminal)

[Unit]
Description=A short description

[Service]
Type=oneshot
ExecStart=/bin/bash /path/to/script.sh

where Description explains what the bash script does. It will be displayed when you list all active services with systemctl, and /path/to/script.sh is your script’s location. You can get it by typing:

readlink -f yourscript.sh

Create a timer that will make systemd run your service every N seconds

The second step is to setup a timer that will ask systemd to run the service you previously created every N seconds. Once again, we’ll use nano to create the file:

sudo nano /etc/systemd/system/name.timer

You need to use the same name string for both files. In the end, you should have created name.service and name.timer.

Once you’re ready to edit the timer file, paste the following content:

[Unit]
Description=A short description

[Timer]
OnUnitActiveSec=360s
OnBootSec=10s

[Install]
WantedBy=timers.target

where Description gives details about the service the timer is associated too, 360 can be replaced by the number of seconds (N) you need. You can leave the rest as it is, OnBootSec is just making the timer run 10 seconds after every startup so that you don’t have to start it manually each time you reboot your machine!

Test your timer and service

The last step is to reload all systemctl daemons, start your timer and check if it’s active. Note that when you start name.timer, it’ll run the service once and then every N seconds.

sudo systemctl daemon-reload
sudo systemctl start name.timer
systemctl list-timers

You should get an output looking like this:

Where your timer should be in the UNIT column and the time left before your service is run another time in the LEFT column.

That’s it! Your bash script and whatever commands it contains will be executed every N seconds, even if you restart your machine.