Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)

Method 1
ps aux | grep -i apt
sudo kill -9 <process_id>

Method 2

sudo lsof /var/lib/dpkg/lock
sudo lsof /var/lib/apt/lists/lock
sudo lsof /var/cache/apt/archives/lock

sudo kill -9 <process_id>

sudo rm /var/lib/apt/lists/lock
sudo rm /var/cache/apt/archives/lock
sudo rm /var/lib/dpkg/lock

sudo dpkg --configure -a

sudo apt update

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