# cat /etc/issue
Ubuntu 16.04.1 LTS \n \l

# apt -fy install cron
E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied)
E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?

# sudo apt install -fy cron
Reading package lists... Done
Building dependency tree       
Reading state information... Done
cron is already the newest version (3.0pl1-128ubuntu2).
0 upgraded, 0 newly installed, 0 to remove and 101 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up cron (3.0pl1-128ubuntu2) ...
Adding group `crontab' (GID 101) ...
Done.
dpkg-statoverride: error: group 'crontab' does not exist
dpkg: error processing package cron (--configure):
 subprocess installed post-installation script returned error exit status 2
Errors were encountered while processing:
 cron
W: No sandbox user '_apt' on the system, can not drop privileges
E: Sub-process /usr/bin/dpkg returned an error code (1)