PrivateTmp=true gives the unit a private mount namespace. The worker's
fuse-overlayfs mount lives only inside that namespace, so the host
cannot see it and the gameserver unit (started via systemctl, with its
own namespace inherited from the host) also cannot see it. The
gameserver unit then fails CHDIR on
/var/lib/left4me/runtime/<name>/merged/left4dead2.
The mount must land in the host namespace so the gameserver unit
inherits it at unshare time. Remaining hardening: dedicated user,
ProtectSystem=full, ReadWritePaths, sudoers allowlist limited to two
helper scripts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The job worker calls fusermount3 (setuid-root) to mount per-instance
FUSE overlays and sudo to invoke the privileged systemctl wrapper.
NoNewPrivileges=true blocks both, surfacing as
"fusermount3: mount failed: Operation not permitted" the first time a
server is started. Hardening is still enforced via dedicated user,
PrivateTmp, ProtectSystem=full, ReadWritePaths, and the narrow sudoers
allowlist limited to two helper scripts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
