1. Prepare a partition for /boot/efi and a partition for /boot in gparted

   |------+-------------+-----------+------+-------+-----------|
   | Name | Mount point | Flag      | Size | FS    | Comment   |
   |------+-------------+-----------+------+-------+-----------|
   | sda1 | /boot/efi   | esp, boot | 300M | FAT32 |           |
   | sda2 | /boot       |           | 2G   | EXT4  |           |
   | sda3 |             |           |      | EXT4  | Encrypted |
   | sda4 |             |           |      | EXT4  | Clear     |
   |------+-------------+-----------+------+-------+-----------|

2. Install clear GNU/Linux on sda4 At manual paritioning step
   • Select sda1
     • Format FAT32
     • Flag esp boot
     • Mount /boot/efi
   • Select sda4
     • Format EXT4
     • Mount /
3. Install crypted GNU/Linux on sda3 At manual paritioning step, check encrypt
   • Select sda1
     • Mount /boot/efi
   • Select sda2
     • Format EXT4
     • Mount /boot
   • Select sda3
     • Delete partition
     • Create parition
     • Check crypt and enter passphrase
     • Mount /
4. Edit grub
   • From crypted GNU/Linux do sudo gedit /etc/default/grub
   • Enable os-prober by uncommenting #GRUB_DISABLE_OS_PROBERfalse`
   • Do

       sudo grub-mkconfig -o /boot/grub/grub.cfg
       reboot

Notes

To have the passphrase aked after kernel selection,

• encrypted GNU/Linux kernels have to be stored on a specific /boot/efi partition (sda2)
• clear GNU/Linux kernels have to be stored in the same partition as clear GNU/Linux (sda4)