Advanced systemd service management: dependencies, drop-ins, and masking.
medium risk
Beyond start/stop/status, systemctl manages service dependencies, unit file overrides (drop-ins), masking (preventing any start), and systemd's boot analysis. Drop-in files in /etc/systemd/system/service.d/ override specific unit directives without editing originals.
systemctl list-dependencies nginx.serviceShow dependency tree for nginx · explain & risk-check →systemctl cat nginx.serviceShow the effective unit file including drop-ins · explain & risk-check →systemctl edit nginx.serviceCreate a drop-in override for nginx unit · explain & risk-check →systemctl mask postfix.servicePermanently prevent postfix from starting (even by dependencies) · explain & risk-check →systemd-analyze blame | head -20Show services ranked by boot time · explain & risk-check →systemd-analyze critical-chainShow the critical path in boot sequence · explain & risk-check →Use `systemctl edit service` for drop-in overrides instead of editing unit files directly — overrides survive package upgrades and are clearly separated in `/etc/systemd/system/service.d/override.conf`.
Reference text is hand-written and may be incomplete — check man systemctl for your version. Test destructive commands on a non-production system first.