find

Find a file anywhere on the hard drive

(While ignoring errors about you not having permissions to see certain folders:

sudo find / -name "filename" 2>/dev/null

Find the most recently modified files in a directory and display their human-readable timestamps

find /some/subdirectory/ -type f -printf '%T@ %p\n' | sort -n | tail -n 10 | awk '{print $2}' | xargs ls -lh --time-style=long-iso