Could not get lock /var/lib/dpkg/lock-frontend. It is held by process 9987 (apt) N: Be aware that removing the lock file is not a solution and may break your system code example

Example 1: 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

Example 2: E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)

sudo rm /var/lib/apt/lists/locksudo rm /var/lib/apt/lists/lock-frontend