Issuing “apt-get update” or “apt-get upgrade” commands resulted in the following error:

E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

I couldn’t locate any running processes which would be locking these files so went ahead and removed the lock files via:

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

And then repeated the commands successfully.