KF2 Dedicated Server on Linux: systemd User Service Unit File

This is a rewritten version of a community guide that shows how to manage a Killing Floor 2 dedicated server on Linux with a systemd user service. It was written on a Gentoo Hardened system but should work similarly on other systemd distributions. The author stresses that nothing is guaranteed: read and understand every command before running it. For installing the server itself see KF2 dedicated server with SteamCMD.

Prerequisites

• A systemd-based distribution.
• A dedicated, unprivileged user for the server (not root, and preferably not in the wheel group, since that is a needless risk).
• SteamCMD and the KF2 dedicated server already installed, and the binary able to start by hand without errors, for example: exec /path/to/killingfloor2_dedicated_server/Binaries/Win64/KFGameSteamServer.bin.x86_64.
• Firewall and port access already prepared (not covered in the guide).
• Root access once, for the linger command.

Notation: commands with $ run as the server user, commands with # as root; drop the prefix when typing.

Example names

User steamserver, home /home/steamserver, unit file kf2-server.service in the user's systemd directory, SteamCMD in /mnt/server/steam/steamcmd and the game in /mnt/server/steam/games/killingfloor2. Change these to suit your system.

Creating the unit file

As the server user, create the directory and file:

$ mkdir -p ~/.config/systemd/user
$ touch ~/.config/systemd/user/kf2-server.service

Content of the file:

[Unit]
Description=Killing Floor 2 Dedicated Server

[Service]
Type=simple
ExecStart=/mnt/server/steam/games/killingfloor2/Binaries/Win64/KFGameSteamServer.bin.x86_64
Restart=on-failure
TimeoutStopSec=30
KillSignal=SIGINT
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

• Description is free text.
• ExecStart must be the full path to the binary, without exec or extra syntax.
• Restart=on-failure restarts the server after a crash; the stop signal is SIGINT (Ctrl-C), with 30 seconds to shut down.

First start as a service

1. Linger. As root, run # loginctl enable-linger steamserver once. The user's processes then survive after the shell is closed, so you do not need screen.
2. Do not use su. Open the user session with $ machinectl shell --uid steamserver (run from a user in the wheel group), or log in from a TTY or the desktop. With su, systemd reports there is no medium to connect to. You must use machinectl on every login to manage the service; an alias helps.
3. Reload. $ systemctl --user daemon-reload. Do this after every change of the unit file, otherwise the old version keeps being used and debugging wastes hours.
4. Start. $ systemctl --user start kf2-server.service. The shell should print nothing; on errors use journalctl --user -u kf2-server.service.
5. Check. $ systemctl --user status kf2-server.service. A healthy status shows "active (running)", the main PID and the server log lines such as DevOnline advertising settings. Then try to join the server in game.

Start at boot

$ systemctl --user enable kf2-server.service or enable and start in one step with enable --now. The author notes a harmless warning that multi-user.target is a non-existent unit for a user instance; reboot to confirm everything starts as intended.

Credits

The author thanks Gentoo and TripWire community helpers, and refers to the systemd documentation and an outdated example unit file from the days before the Linux KF2 server binary existed. The text is released with no restrictions.