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linuxbashubuntusystemd

How to set ExecStart from function output in systemd config file?

I created a systemd service file in directory /lib/systemd/system/ to launch nodejs as a service. The problem is that the file contains hardcoded path to nodej in ExecStart field. It means that any time I update nodejs I will have to manually change this service file. Is there a way to use which node command in the file below to automatically set the path?

[Unit]
Description=node-server-1
After=network.target

[Service]
Environment=NODE_PORT=3001
Type=simple
User=manid
ExecStart=/home/manidos/.nvm/versions/node/v14.15.1/bin/node /home/manidos/node-nginx/index.js
Restart=on-failure

[Install]
WantedBy=multi-user.target
Solution

  • You can run a simple bash script within the ExecStart line:

    ExecStart=/bin/bash -c '$$(/usr/bin/which node) /home/manidos/node-nginx/index.js'

    Basically, this is running the which command in a subshell and passing its stdout to be run by the outer script. Double-dollars are needed to use this particular syntax in a systemd unit file, as documented in the systemd.service manpage.