phoenixnap.com/kb/fix-could-not-get-lock-error-ubuntu
E: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 12611 (unattended-upgr)
N: Be aware that removing the lock file is not a solution and may break your system.
E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?