/usr/lib/systemd/system/gdm.service calls /usr/bin/gdm --nodaemon Now /usr/bin/gdm is a shell script that starts gdm in background, and does not have a --nodaemon option. Calling /usr/sbin/gdm-binary directly fixes the issue. Reproducible: Always Steps to Reproduce: boot with systemd start gdm
Also see the related discussion at #435042 for this systemd issue and more.
Should be fixed in 3.6.0, which reintroduces the --nodaemon patch, and uses a more systemd-friendly pam.d configuration.