Recursively delete every file with a certain extension (safely) — by Radu Rădeanu on Ask Ubuntu

Shows how to make your user own a folder and everything inside it with chown -R, and optionally the group too. It's useful when files created with sudo have become unwritable.

du -hs gives a single human-readable total for a folder. The answer explains the -h (human-readable) and -s (summary) flags and how to sort folder sizes.

On Ubuntu, members of the sudo group can already use sudo, so you just add the user to that group instead of editing /etc/sudoers. The change takes effect at the user's next login.