Systemd Service Unit Restrictions: A Common Cause of Daemon Startup Failures
2025-09-20
A classic problem for Linux system administrators is a daemon failing to start normally but working fine when manually run as root. Traditional causes include incomplete $PATH environment variables, SELinux, and AppArmor. Increasingly, systemd service unit restrictions (documented in systemd.exec) are the culprit. Directives like ProtectHome and PrivateTmp can cause cryptic 'permission denied' or 'file not found' errors, or even indirect failures like blocking DNS queries. Removing restrictions from the daemon's .service file can help diagnose the issue, but future daemons may rely on these restrictions, complicating troubleshooting.
Development
daemon