E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), code example

Example 1: E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?

sudo kill -9 PID
sudo rm /var/lib/dpkg/lock-frontend
sudo apt update

Example 2: E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?

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