update systemctl cli guide

pages/linux/systemctl.md

@@ -1,6 +1,6 @@
 # systemctl
 
-> Control the systemd system and service manager. You may need to run with `sudo` prefix to avoid permission denied issues.
+> Control the systemd system and service manager.
 > More information: <https://www.freedesktop.org/software/systemd/man/systemctl.html>.
 
 - Show all running services:
@@ -19,11 +19,7 @@
 
 `systemctl {{enable|disable}} {{unit}}`
 
-- Mask/Unmask a unit to prevent enablement and manual activation:
-
-`systemctl {{mask|unmask}} {{unit}}`
-
-- Reload systemd, scanning for new or changed units:
+- Reload systemd, scan for new or changed units:
 
 `systemctl daemon-reload`
 
@@ -34,3 +30,7 @@
 - List all units of service/socket/automount filter by running/failed state:
 
 `systemctl list-units --type={{service|socket|automount}} --state={{failed|running}}`
+
+- Show the source unit files:
+
+`systemctl cat {{unit}}`