How to remove missing systemd units?

The command you're after is systemctl reset-failed

When systemd analyzes unit definition files, it takes note of any other related units called out in the file - whether those other units exist or not.

$ systemctl --state=not-found --all
> ( ...prints list of 'not-found' units )

$ grep -r "<missing-unit>" /usr/lib/systemd/system
> ( returns files with references to <missing-unit> )

When a unit shows up as "not-found", it's not necessarily an error - all we know is, a local unit definition claims to have some relationship with it. This relationship might not be one we care about. For example, it could be "Before:" some other unit, but we don't use that other unit.

• failed - happens when a unit has entered a failed state and can be reset with the systemctl reset-failed command
• not-found - happens when you've removed a unit but systemd still has a reference to it, like when a unit gets enabled and a symlink gets placed in /etc/systemd/system, this can be fixed by removing references to the unit in /etc/system/systemd/*.wants/ then running systemctl daemon-reload

For example, assume the following bash script:

#!/bin/bash
# script.sh
while true
do
    sleep 1
done

And 3 systemd units: example-foo.service, example-bar.service, and example-baz.service

$ sudo systemctl cat example-{foo,bar,baz}.service
# /etc/systemd/system/example-foo.service
[Service]
ExecStart=/home/vagrant/script.sh
[Install]
WantedBy=multi-user.target

# /etc/systemd/system/example-bar.service
[Service]
ExecStart=/home/vagrant/script.sh
[Install]
WantedBy=multi-user.target

# /etc/systemd/system/example-baz.service
[Service]
ExecStart=/home/vagrant/script.sh
[Install]
WantedBy=multi-user.target

Now, let's start and enable the units. Observe how symlinks get created.

$ sudo systemctl start example-{foo,bar,baz}.service
$ sudo systemctl enable example-{foo,bar,baz}.service
Created symlink from /etc/systemd/system/multi-user.target.wants/example-foo.service to /etc/systemd/system/example-foo.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/example-bar.service to /etc/systemd/system/example-bar.service.
Created symlink from /etc/systemd/system/multi-user.target.wants/example-baz.service to /etc/systemd/system/example-baz.service.

Confirm there are actually 6 files for our 3 units.

$ find /etc/systemd/system -name 'example*.service'
/etc/systemd/system/multi-user.target.wants/example-bar.service
/etc/systemd/system/multi-user.target.wants/example-foo.service
/etc/systemd/system/multi-user.target.wants/example-baz.service
/etc/systemd/system/example-bar.service
/etc/systemd/system/example-foo.service
/etc/systemd/system/example-baz.service

Now, check the state of all 3 units, they're running.

$ systemctl list-units example*
UNIT                LOAD   ACTIVE SUB     DESCRIPTION
example-bar.service loaded active running example-bar.service
example-baz.service loaded active running example-baz.service
example-foo.service loaded active running example-foo.service

Now, simulate a failure by sending a SIGKILL to example-foo.service. Observe how the unit is in a failed state.

$ sudo systemctl kill -s KILL example-foo.service
$ systemctl list-units example*
  UNIT                LOAD   ACTIVE SUB     DESCRIPTION
  example-bar.service loaded active running example-bar.service
  example-baz.service loaded active running example-baz.service
● example-foo.service loaded failed failed  example-foo.service

To reset a unit in a failed state use the systemctl rese-failed command. Observe how the unit is now in an inactive state.

$ sudo systemctl reset-failed
$ systemctl list-units example*
UNIT                LOAD   ACTIVE SUB     DESCRIPTION
example-bar.service loaded active running example-bar.service
example-baz.service loaded active running example-baz.service

...
$ systemctl list-units --all example*
UNIT                LOAD   ACTIVE   SUB     DESCRIPTION
example-bar.service loaded active   running example-bar.service
example-baz.service loaded active   running example-baz.service
example-foo.service loaded inactive dead    example-foo.service

Okay, now let's remove the example-bar.service unit. Observe how the unit is in a not-found state; however, the example-bar.service broken symlink is still in /etc/system/system/multi-user.target.wants

$ sudo rm /etc/systemd/system/example-bar.service
$ sudo systemctl daemon-reload
$ sudo systemctl stop example-bar.service
Failed to stop example-bar.service: Unit example-bar.service not loaded.
$ systemctl list-units --all example*
  UNIT                LOAD      ACTIVE   SUB     DESCRIPTION
● example-bar.service not-found inactive dead    example-bar.service
  example-baz.service loaded    active   running example-baz.service
  example-foo.service loaded    inactive dead    example-foo.service
$ find /etc/systemd/system -name 'example*.service'
/etc/systemd/system/multi-user.target.wants/example-bar.service
/etc/systemd/system/multi-user.target.wants/example-foo.service
/etc/systemd/system/multi-user.target.wants/example-baz.service
/etc/systemd/system/example-foo.service
/etc/systemd/system/example-baz.service

Remove the broken symlink and confirm the example-bar.service unit is gone.

$ sudo rm /etc/systemd/system/multi-user.target.wants/example-bar.service
$ sudo systemctl daemon-reload
$ systemctl list-units --all example*
UNIT                LOAD   ACTIVE   SUB     DESCRIPTION
example-baz.service loaded active   running example-baz.service
example-foo.service loaded inactive dead    example-foo.service

It seems that systemd maintains links but does not know what to do with them when you delete the unit file.

You could try to remove them manually in /etc/systemd/system/suspend.target.wants/ and such but of course systemctl reset-failed from a previous answer sounds like a better option.

$ cd /etc/systemd/system
$ sudo mv lock.service /tmp 
$ sudo systemctl disable lock.service
Failed to disable unit: No such file or directory
$ sudo mv /tmp/lock.service .
$ sudo systemctl disable lock.service
Removed /etc/systemd/system/suspend.target.wants/lock.service.