Performing pre-shutdown tasks

Why I wanted to do this

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I remember losing most of my notes in my second semester of diploma. It hurt my soul. Despite having a private github repository setup for said notes, the process was still manual as I had to run the commands to add, commit and then push. This made it so I only backed up my notes once a week. One time I wanted to do some deleting and stupidly I did not test out the script in a dummy folder beforehand. This resulted in me deleting a lot of important documents. After that experience all I wanted to do was to be able to have this backup process happen on its own. So, I came up with a simple solution: Performing the add, commit and push before the computer shutsdown. I spent some time looking at options to achieve what I wanted and I managed to find a solution I’m quite happy with.

First of all this doesn’t apply to just before shutdowns. You can use systemd in a variety of ways. If you’d like to know more about what systemd is refer to this article and if you’d like to how to run certain scripts based on some condition refer to the article on systemd on the arch wiki and the man page about systemd.

Creating systemd units

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Tasks ran by systemd are called units and all units have the .service extension. These units are made by users and therefore must be placed in ~/.config/systemd/user/¹. Thank the Arch Wiki because there’s a guide that tells you exactly how to write units. Based on the functionality desired I wrote a simple script (stored in ~/script to keep things simple) and then made it executable with chmod u+x <script>.²

I named the unit backup.service and placed it in ~/.config/systemd/user. You can name it whatever you want, as long as it’s name clearly describes its purpose. This is the content of the unit.

[Unit]
Description=Backup obsidian notes before shutdown
DefaultDependencies=no
Requires=network-online.target
After=network-online.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStop=fish /home/yjh/scripts/backup.fish

[Install]
WantedBy=default.target shutdown.target

It took me a while to figure out what the purpose of [Install] is and if you’d like to know more take a look at the man page for this.

There are a few items that relate to my use case of (1) running scripts before shutdown and (2) pushing a local repo to a remote repsitory.

• RemainAfterExit, ExecStop is for service units that will run scripts.

RemainAfterExit³ is a must for these service units as it won’t even get into an active state it will always be dead.⁴

• Requires=network-online.target

Requires= makes sure that network-online.target will be started if it isn’t when this service unit activates. This is because to push to remote repository an internet connection is required.

• After=network-online.target

After= makes sure that network-online.target has started. If network-online.target fails to start for whatever reason the script will not be executed.⁵ This ensures that the script will only execute if there is an internet connection otherwise, nothing happens.

Something very important that I’d like to bring up is the help I received from dnaka and Freddy a unix user who helped me solve this issue. He also explained that if DefaultDependencies is removed then shutdown.target is implicitly included when the service unit is run!

Working around user input

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After password authentication was shutdown in 2021, I decided to use SSH keys for authorisation. However, my SSH keys are password protected which means that user input is required. Inputs which I cannot give because when the system is shutting down the screen goes black. So, a way to circumvent this is to create a new SSH key and only use it for that specific repository. GitHub already has documentation on how to do exactly that.

Enabling the unit

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After writing up the service unit they are not detected yet and systemd will need to know about them to do that run sudo systemctl daemon-reload. Then you’ll need to enable it with systemctl --user enable <service> and there will be some output this is what I got.

Created symlink /home/yjh/.config/systemd/user/shutdown.target.wants/backup.service → /home/yjh/.config/systemd/user/backup.service.

I made some random changes and I restarted my PC. I looked at the repository through my phone and saw a new commit. A huge success!

Closing thoughts

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This actually took me a while to deal with. I spent many hours on this and even skipped class, probably not a smart idea. I was in class sure, but I was at the back doing my own thing. Anyways, the moral of the story is

1. Don’t run rm -rf without testing it first.
2. Automate backups for redundency.

I implemented this about two years ago, and I’ve never been happier at my lack of data loss. I even manually backup my data once every few months to an external drive I carry around everywhere. I’m proud to say that if you threw my laptop into a volcano I would suffer no data loss!