SHELL

E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable) E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?

ps aux | grep -i apt

sudo kill <process_id>
# Check if the process was killed by running the ‘ps aux | grep -i apt’ command. If it is still running, force kill it with SIGKILL signal:

sudo kill -9 <process_id>
# Another, easier way would be to use the killall command. This will kill all the instances of a running program:

sudo killall apt apt-get

waiting for cache lock, Could not get lock /var/lib/dpkg/lock-frontend.

sudo lsof /var/lib/dpkg/lock
or 
sudo lsof /var/lib/apt/lists/lock
or
sudo lsof /var/lib/dpkg/lock-frontend

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.

Ubuntu Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 15551 (apt)

Ubuntu: Waiting for cache lock: Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 15551 (apt)