# Systemd Service Files

Files used to interact with systemd.

There are additional tools on the horizon to replace systemd, but it has remained standard and likely will for the foreseeable future.

One use case of defining your own systemd file is to trigger a third-party screen lock based on system events.

I have written a custom “lock” script which wraps i3lock-color. Without a custom script one could use /usr/bin/i3lock as the ExecStart.

The below file could be saved at /etc/systemd/system/i3lock.service.

Enabling it requires running sudo systemctl enable i3lock.service.

Now whenever the system is triggered to sleep or suspend it will invoke the lock script.

[Unit]
Description=Lock the screen with i3lock
# Ensure that we run this service before the machine can actually go to sleep
Before=sleep.target

[Service]
User=daylin
Type=forking
Environment=DISPLAY=:0
ExecStart=/home/daylin/bin/lock

[Install]
# Ensure that this is called when we're trying to suspend the machine
WantedBy=suspend.target

## Transitioning the above for NixOS

In NixOS systemd service files can be specified directly in the system configuration as a nix expression.

The above might be added as follows:

{
  pkgs,
  ...
}: {
    environment.systemPackages = with pkgs; [
    i3lock-color
    figlet # for ~/bin/lock -> i3lock-color
  ];


  systemd.services.i3lock = {
    wantedBy = ["sleep.target"];
    description = "Lock the screen using a custom lock script";
    before = ["suspend.target"];
    path = with pkgs; [ bash procps figlet i3lock-color];
    serviceConfig = {
      User = "daylin";
      Type = "forking";
      Environment = "DISPLAY=:0";
      ExecStart = "${pkgs.bash}/bin/bash /home/daylin/bin/lock";
      };
  };
}

Most of the arguments are straightforward taken from man systemd.unit. One that I think is nix specific is the path argument which will add each of the specified packages to the environment of the unit using Environment=PATH=/nix/store/path/to....

Ideally, my lock script which is managed by chezmoi would exist as an actual package defined in my system configuration that is itself a wrapper for figlet and i3lock-color.