Problem: SSH Login is not Possible and apt Shows Errors

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apt
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#1

Problem: SSH Login is not possible and apt shows errors

Besides of the two services ssh and apt others services might be affected and show similar error messages.
Tryning to install software results in fatal error:

Use of uninitialized value in concatenation (.) or string at /usr/share/perl5/Debconf/Config.pm line 22.
Vorkonfiguration der Pakete ...
dpkg: nicht behebbarer fataler Fehler, Abbruch:
unbekannter Benutzer »geoclue« in statoverride-Datei
Reading package lists... Done
Building dependency tree      
Reading state information... Done
W: No sandbox user '_apt' on the system, can not drop privileges
E: Sub-process /usr/bin/dpkg returned an error code (2)

id command might show confusing errors and it is not possible to restart ssh service.

Solution

The files /etc/passwd and /etc/group have been deleted by error.

Restore these files from backup or copy them from a different UCS host (Note: when copying make sure those two servers have similar packages installed in order to have matching users or groups).