Specialised and general cleaning.
From an Ubuntu live ISO
- Delete unwanted files
- Alternatively, reformat drive with GParted (already installed on Ubuntu live ISO)
- Enable Universe repository with sudo add-apt-repository universe
- Alternatively, open Software Sources and tick Community-maintained software (universe)
- Update (sudo apt update)
- Install Bleachbit (sudo apt install bleachbit)
- Open Bleachbit
- Wipe free space on the drive
Alternatively (no need for new installation):
- Reformat drive with GParted
- sudo shred -vzn1 /dev/sda # careful!