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[Solved] How can I make a custom .service run as root? (reddthat.com)
submitted 4 months ago* (last edited 4 months ago) by [email protected] to c/[email protected]
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cross-posted from: https://reddthat.com/post/21668140

I have a VPN daemon that needs to run before the client will work. Normally, this would have been set up automatically by its install script, but the system is immutable.

I've created the systemd service via sysyemctl edit --force --full daemon.service with the following parameters:

[Unit] 
Description=Blah
After=network-online.target

[Service]
User=root
Group=root
ExecStart=/usr/bin/env /path/to/daemon

[Install]
WantedBy=multi-user.target

I've verified that the daemon is actually executable, and it runs fine when I manually call it via sudo daemon. When I try to run it with sudo systemctl enable --now daemon.service, it exits with error code 126.

What am I missing?

Edit: Typo, and added the relevant user and group to the Service section. Still throwing a 126.

Solution: the system wanted /usr/bin/env in ExecStart to launch the binary. The .service file above has been edited to show the working solution.

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[–] [email protected] 3 points 4 months ago* (last edited 4 months ago) (1 children)

Try ExecStart=/usr/bin/env /path/to/daemon
Also what's the output of ldd /path/to/daemon & sudo systemd-run /path/to/daemon ? Maybe check systemctl show-environment. Maybe try adding Type=simple , this tells systemd that the service will fork.

If that fails, we could try ExecStart=/usr/bin/strace -f -o /tmp/daemon_strace.log /path/to/daemon for stactrace & ExecStart=/bin/sh -c '/path/to/daemon > /tmp/daemon.log 2>&1' to log the daemon.

[–] [email protected] 3 points 4 months ago* (last edited 4 months ago) (1 children)

Omg, adding /usr/bin/env worked. Launched the daemon, and the client is able to launch and connect a WireGuard tunnel.

systemctl show-environment lists /usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin on the PATH, so maybe that's why that worked...? (I'm going to have to go read up on env).

Either way, I did a reboot to verify, and it's definitely running. Now I just need to tweak it a bit so it tries to reconnect if the network drops out, but holy shit, I appreciate the help.

[–] [email protected] 3 points 4 months ago

Good to hear that it worked.
To explain env, typically when systemd is running a service it only provides a very minimal environment. When using env it passes more of the environment variables and whatnot from userspace, so it's likely that the binary daemon was looking for specific environment variables and it returned an empty string and that's what caused error, it's also useful if the daemon's location changes during runtime or if it's not in a standard location.