│ └─8105 /usr/sbin/apache2 -k start
zyga@gracik:/etc/systemd/network$ systemctl --failed
  UNIT              LOAD      ACTIVE SUB    DESCRIPTION                                                                                                                                                                                       
● snap-repair.timer not-found failed failed snap-repair.timer                                                                                                                                                                                 

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.

1 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.