Error while trying to install openssh-server on Buster

[rhkramer <rhkramer.s32@gmail.com>]

I get this error when trying to apt-get install openssh-server on my (up to 
date) Buster system:

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

I tried (based on the reference below):

root@s32:/# systemctl unmask org.freedesktop.systemd1.UnitMasked
Unit org.freedesktop.systemd1.UnitMasked.service does not exist, proceeding 
anyway.

I don't really have a clue.  One googled page suggests 

<quote>
Situation

Checking the status of a service shows it is masked.

Running systemctl unmask <unit file> doesn't change the status.


Resolution
The systemd unit file is empty.  Replace it in /usr/lib/systemd/system by 
reinstalling the package in which the unit file was contained.
</quote>