Installing systemd service unit in a formula

[EvanDurfee]

Additional Info

• I am using Windows Subsystem for Linux

Output of brew config

HOMEBREW_VERSION: 4.6.20-80-gbc9ec8b
ORIGIN: https://github.com/Homebrew/brew
HEAD: bc9ec8b11b43e1cbe0202d75784c8e3307e0b062
Last commit: 4 hours ago
Branch: main
Core tap JSON: 10 Nov 06:55 UTC
HOMEBREW_PREFIX: /home/linuxbrew/.linuxbrew
HOMEBREW_BROWSER: firefox
HOMEBREW_BUNDLE_USER_CACHE: /var/home/evan/.cache/bundle
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: :0
HOMEBREW_DOWNLOAD_CONCURRENCY: 32
HOMEBREW_EDITOR: nano
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_MAKE_JOBS: 16
HOMEBREW_SORBET_RUNTIME: set
SUDO_ASKPASS: /usr/libexec/openssh/gnome-ssh-askpass
Homebrew Ruby: 3.4.5 => /var/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/3.4.5/bin/ruby
CPU: 16-core 64-bit zen5
Clang: N/A
Git: 2.51.1 => /bin/git
Curl: 8.11.1 => /bin/curl
Kernel: Linux 6.16.10-200.fc42.x86_64 x86_64 GNU/Linux
OS: Bluefin (Version: 42.20251102.1) (Deinonychus)
Host glibc: 2.41
Host libstdc++: 6.0.34
/usr/bin/gcc: 15.2.1
/usr/bin/ruby: N/A
glibc: N/A
gcc@12: N/A
gcc: N/A
xorg: N/A

Output of brew doctor

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Description of issue

I'm trying to write a simple formula for linux that installs a shell script to libexec and adds a systemd user unit. However, I can't seem to figure out how to install the service file. The formula cookbook says:

If the package already provides a service file the formula can reference it by name:

service do
  name macos: "custom.launchd.name",
       linux: "custom.systemd.name"
end

But there's no mention of how to install service files.
Here's the formula in question:

class FreedesktopColorSchemeMonitor < Formula
  # ...
  depends_on :linux

  def install
    modified_file = File.read("systemd/color-scheme-monitor.service")
                        .gsub!("ExecStart=/usr/libexec/color-scheme/color-scheme-monitor.sh",
                               "ExecStart=#{prefix}/libexec/color-scheme-monitor.sh")
    File.write("color-scheme-monitor.service", modified_file)

    libexec.install "color-scheme/color-scheme-monitor.sh" => "color-scheme-monitor.sh"
    # This seems like where brew services look for the file, but installing here breaks the installation badly
    # opt_prefix.install "color-scheme-monitor.service" => "color-scheme-monitor.service"
  end

  service do
    name linux: "color-scheme-monitor"
  end

  test do
    system "test", "-e", "#{libexec}/color-scheme-monitor.sh"
  end
end

I can't really replace the systemd unit with a generic brew service in this case, since the service needs to run after another service has already started. How does one handle service files on linux?

[gromgit]

IIRC, service files go in the keg's root directory, so after you've written out your service file:

prefix.install "color-scheme-monitor.service"

[EvanDurfee]

That did the trick! Thanks.