The TwinCAT System Service

The TwinCAT system service is managed via a systemd service file, which is located in the /lib/systemd/system/TcSystemServiceUm.service directory.

To check whether the service is running, use the following command:

systemctl status TcSystemServiceUm

Press [q] to exit the status view.

If the service is running correctly, an output similar to the following should be displayed:

● TcSystemServiceUm.service - TwinCAT Usermode System Service
     Loaded: loaded (/usr/lib/systemd/system/TcSystemServiceUm.service; enabled; preset: enabled)
     Active: active (running) since Thu 2025-09-04 08:24:07 UTC; 6s ago
 Invocation: eef60162fcd44307ba2358a4844d4ce6
   Main PID: 1746 (TcSystemService)
      Tasks: 30 (limit: 4596)
     Memory: 396M (peak: 396.6M)
        CPU: 428ms
     CGroup: /system.slice/TcSystemServiceUm.service
             └─1746 /usr/bin/TcSystemServiceUm -f 0x5 -p /var/run/TcSystemServiceUm.pid
Sep 04 08:24:06 PC-6A4593 TcSystemServiceUm[1746]: 2025-09-04 08:24:06.907033 - Init client interface
Sep 04 08:24:06 PC-6A4593 TcOs[1746]: Error -1 calling init_devd_notification(). System start continued.
Sep 04 08:24:06 PC-6A4593 TcOs[1746]: StartSystem: ProcessorInfo:4 1 1

--snipped--

You can start and stop the TwinCAT system service and check its status by using the command systemctl:

sudo systemctl stop TcSystemServiceUm
sudo systemctl status TcSystemServiceUm
sudo systemctl start TcSystemServiceUm