I cannot install new packages: "Could not get lock /var/lib/dpkg/lock"

Do you have the GUI package manager/or update manager programs running? If so there's a conflict, simply close those programs down and your command line should work.

This should be used as last resource. If you use this carelessly you can end with a broken system. Please evaluate other answers first before trying this. You can delete the lock file with the following command:

sudo rm /var/lib/dpkg/lock

After that, try installing again.