could not get lock /var/lib/dpkg/lock-frontend. It is held by process 6800 (apt-get code example

Example 1: how to realse the lock in the linux in apt

sudo kill <process_id>

Example 2: why upgrade ubuntu then frequently shows this message "It iwating for cache lock: Could not get lock /var/lib/dpkg/lock.frontend.

It iwating for cache lock: Could not get lock /var/lib/dpkg/lock.frontend.