The Linux installer runs Traccar as root by default. You can change this using a systemd service override.
Create a user named traccar, unless it already exists:
sudo useradd --system --user-group --no-create-home --shell /usr/sbin/nologin traccar
Stop Traccar and give the user access to its data, logs and media:
sudo systemctl stop traccar
sudo mkdir -p /opt/traccar/data /opt/traccar/logs /opt/traccar/media
sudo chown -R traccar:traccar /opt/traccar/data /opt/traccar/logs /opt/traccar/media
The user must also be able to read the application files and conf/traccar.xml. Adjust paths and permissions if you have customized your installation.
Run sudo systemctl edit traccar and add:
[Service]
User=traccar
Group=traccar
Then start the service:
sudo systemctl daemon-reload
sudo systemctl start traccar
If it fails to start, check journalctl -u traccar for permission errors.