I am running one node service on a linux host that should be started on system startup but since I don't have root on the machine, this requires a user systemctl service

To set up pm2 to start as systemctl a minor trickery is required to get the environment right so that pm2 finds its config files

First of all, create a service file in ~/.config/systemctl/user.control/pm2.service

[Unit]
Description=pm2

[Service]
Type=simple
StandardOutput=journal
ExecStart=/home/username/node_modules/pm2/bin/pm2 restart all
EnvironmentFile=-/home/username/pm2_env.txt

[Install]
WantedBy=default.target

go to the node project dir and start it if you have not done so already

cd ~/project
pm2 start
pm2 save

Dump the environment to a file to make sure that the PATH environment is correct, this may or may not be required, the path is what pm2 startup systemd suggests

env PATH=$PATH:/nix/store/7y1qagav6xv4k3w0df5d7z91y2d3w4z7-nodejs-18.13.0/bin >~/pm2_env.txt

not all environment settings are necessary, you can remove the ones that relate to programs that are not used during the startup process like ssh or X

start the service as systemctl service, this will restart the pm2 process and all defined processes

systemctl --user restart pm2.service

set the service to be started on boot

systemctl --user enable pm2.service

when the service is running it should display successful startup when running, as the pm2 program forks and exists, it is listed as dead/inactive, that is correct

systemctl --user status pm2.service

and

pm2 logs

should show logs