How to write a Systemd unit that will fire before networking goes down

systemd

I want to run a script when a user shuts their computer down, but it needs networking. So I'd like it to run when the system is heading for shutdown (or restart), but it needs to run before anything is unmounted or networking is shut off.

How can I do this?

Best Answer

This question is very similiar to How to run a script with systemd right before shutdown?. With the twist that you want to be sure networking is up.

To cover that, add this to your service file:

After=networking.service

As the docs say, After= not only declares that your service is started by the networking service, it also is declaring that the services should be stopped in the inverse order-- before networking is shut down.

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Execute code on shutdown on Fedora 19

The signal can be caught from a running process. So, if you start a long-living process (aka daemon) on boot-up, then you will indeed receive a SIGTERM from that process and do whatever you want from the signal handler. However, this is the worst method possible: an extra process doing nothing and just waiting for a signal to arrive.

You have better ways to achieve this, esp. with systemd. The unit file (foo.service) will look as following:

[Unit]
Description=Perform my actions
DefaultDependencies=no
Before=shutdown.target

[Service]
Type=oneshot
ExecStart=/path/to/your/application

However, keep in mind that due to parallel nature of systemd this unit can be started arbitrarily late in the shutdown process (although this can be influenced by careful use of dependencies).

Trigger systemd Unit on Suspend Before Networking Shutdown – How to

Inspired by https://unix.stackexchange.com/a/139664/160746 I upgraded my start/stop scripts to a full blown daemon and made it listen for PrepareToShutdown signal. This is a race against NetworkManager every start/stop, but it seems to work reliably on my system.

I have uploaded my code and systemd unit at https://github.com/davidn/av.

Best Answer

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Execute code on shutdown on Fedora 19

Trigger systemd Unit on Suspend Before Networking Shutdown – How to

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