An error occurred while installing the. DEB file with dpkg
dpkg: error: dpkg frontend is locked by another process
solution:

sudo rm /var/lib/dpkg/lock
sudo rm /var/lib/dpkg/lock-frontend 
sudo rm /var/cache/apt/archives/lock 

You can remove the error
re enter the command to install DEB files to install

sudo dpkg -i xxxxxx.deb