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'```

