Disable user

Disable the user named guestuser from logging in, including via ssh

sudo usermod --expiredate 1 guestuser

Text search

Look for text in all files in the current directory recursively

grep -Hrn <text> .

Disk usage

List all available partitions to mount

lsblk

Mount drive the easy way

udisksctl mount -b /dev/sd[letter][number]

Files

File copier with progress bar

rsync -vau