Setting up xserver-xephyr (2:1.18.4-0ubuntu0.2) ...
Setting up xserver-xorg-legacy (2:1.18.4-0ubuntu0.2) ...
setting xserver-xorg-legacy/xwrapper/allowed_users from configuration file
Setting up xserver-xorg-core (2:1.18.4-0ubuntu0.2) ...
Processing triggers for libc-bin (2.23-0ubuntu4) ...
Errors were encountered while processing:
 shim-signed
E: Sub-process /usr/bin/dpkg returned an error code (1)