Ошибка gdbus error org freedesktop systemd1 unitmasked unit mount is masked

(Dist: Debian 10)

I have a reoccurring error message that mainly pops up when using systemctl (also when installing a package, and occasionally in a few other places that escape me),

Unit -.mount is masked.

Sometimes (depending on what command called the error message) it is more verbose, such as

Error: GDBus.Error:org.freedesktop.systemd1.UnitMasked: Unit -.mount is masked.

This error doesn’t impede installing packages or any systemd services which are enabled already (and as such are loaded at boot), but using systemctl or service to restart, start or stop a service fails. This means I have to reboot the whole server to restart a service, which can be a little annoying.

Trying to unmask the root mount with systemctl unmask -- -.mount appears to work (nothing is returned), but systemctl status -- -.mount still outputs the following after:

● -.mount - Root Mount
   Loaded: masked (Reason: Unit -.mount is masked.)
   Active: active (mounted) since Mon 2019-08-05 15:03:38 AEST; 4h 8min ago
    Where: /
     What: /dev/sde1
    Tasks: 0 (limit: 4915)
   Memory: 0B
   CGroup: /system.slice/-.mount

Any ideas? I’m don’t want to start from a fresh install for this server, so either I find a fix or just deal with having to restart if I need to reload a service.

On my fresh install of Pop!_OS 19.04 I tried executing sudo apt update followed by sudo apt upgrade and this error happened:
Error: GDBus.Error:org.freedesktop.systemd1.UnitMasked: Unit -.mount is masked. What is causing this error?

This has never happened before and I’m not sure what would have caused it. I tried using sudo apt autoremove and this didn’t help.

$ sudo apt update
Hit:1 http://us.archive.ubuntu.com/ubuntu disco InRelease
Hit:2 http://apt.pop-os.org/proprietary disco InRelease                                            
Hit:3 http://ppa.launchpad.net/system76/pop/ubuntu disco InRelease                                 
Get:4 http://us.archive.ubuntu.com/ubuntu disco-security InRelease [97.5 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu disco-updates InRelease [97.5 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu disco-backports InRelease [88.8 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu disco-updates/main Sources [90.3 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu disco-updates/main i386 Packages [218 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu disco-updates/main amd64 Packages [259 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu disco-updates/universe amd64 Packages [299 kB]
Get:11 http://us.archive.ubuntu.com/ubuntu disco-updates/universe i386 Packages [295 kB]
Fetched 1,444 kB in 4s (389 kB/s)                                               
Error: GDBus.Error:org.freedesktop.systemd1.UnitMasked: Unit -.mount is masked.
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.

$ sudo apt upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
4 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] 
Setting up cups-daemon (2.2.10-4ubuntu2.1) ...
Failed to restart cups.service: Unit -.mount is masked.
invoke-rc.d: initscript cups, action "restart" failed.
● cups.service - CUPS Scheduler
   Loaded: loaded (/lib/systemd/system/cups.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-09-03 15:02:28 CDT; 1h 21min ago
     Docs: man:cupsd(8)
 Main PID: 816 (cupsd)
    Tasks: 1 (limit: 4489)
   Memory: 4.5M
   CGroup: /system.slice/cups.service
           └─816 /usr/sbin/cupsd -l

Sep 03 15:02:28 pop-os systemd[1]: Started CUPS Scheduler.
dpkg: error processing package cups-daemon (--configure):
 installed cups-daemon package post-installation script subprocess returned error exit status 1
Setting up uuid-runtime (2.33.1-0.1ubuntu3) ...
Failed to restart uuidd.service: Unit -.mount is masked.
invoke-rc.d: initscript uuidd, action "restart" failed.
● uuidd.service - Daemon for generating UUIDs
   Loaded: loaded (/lib/systemd/system/uuidd.service; indirect; vendor preset: enabled)
   Active: inactive (dead)
     Docs: man:uuidd(8)
dpkg: error processing package uuid-runtime (--configure):
 installed uuid-runtime package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of cups-core-drivers:
 cups-core-drivers depends on cups-daemon (>= 2.2.10-4ubuntu2.1); however:
  Package cups-daemon is not configured yet.

dpkg: error processing package cups-core-drivers (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of cups:
No apport report written because the error message indicates its a followup error from a previous failure.
                                                                                                           cups depends on cups-core-drivers (>= 2.2.10-4ubuntu2.1); however:
  Package cups-core-drivers is not configured yet.
 cups depends on cups-daemon (>= 2.2.10-4ubuntu2.1); however:
  Package cups-daemon is not configured yet.

dpkg: error processing package cups (--configure):
 dependency problems - leaving unconfigured
No apport report written because MaxReports is reached already
                                                              Errors were encountered while processing:
 cups-daemon
 uuid-runtime
 cups-core-drivers
 cups
Error: GDBus.Error:org.freedesktop.systemd1.UnitMasked: Unit -.mount is masked.
E: Sub-process /usr/bin/dpkg returned an error code (1)

I am wondering what is causing these errors:

Error: GDBus.Error:org.freedesktop.systemd1.UnitMasked: Unit -.mount is masked.
E: Sub-process /usr/bin/dpkg returned an error code (1)

...
Processing triggers for libvlc-bin:armhf (3.0.12-0+deb10u1+rpt3) ...
Error: GDBus.Error:org.freedesktop.systemd1.UnitMasked: Unit -.mount is masked.
pi@raspberrypi400:~/PiUSBCamera $ timedatectl 
Failed to query server: Unit -.mount is masked.
pi@raspberrypi400:~/PiUSBCamera $ 

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