Keeps missing =>

You can use CryptSetup on #Linux: (assuming `sudo` in front of each command)

```cryptsetup luksFormat /dev/mmcblk0

cryptsetup luksOpen /dev/mmcblk0 opt

ls -arlt /dev/mapper | tail

ls -l /dev/mapper/opt

mkfs -t ext4 /dev/mapper/opt```

Where we've named the encrypted drive `opt` and opened in the systems /opt directory, -t is type ext4 which works on Linux systems

```mount /dev/mapper/opt /opt

umount /opt

cryptsetup luksClose opt

ls -l /dev/mapper/opt

'no such file'```