ubuntu@ubuntu:~$ sudo -i
root@ubuntu:~# cryptsetup luksOpen /dev/sda5 bla
Enter passphrase for /dev/sda5: 
root@ubuntu:~# mount /dev/mapper/ubuntu--vg-root /mnt
root@ubuntu:~# umount /media/ubuntu/0eed874a-af2e-4966-a2be-2daa2df6cd64 #boot partition
root@ubuntu:~# mount /dev/sda1 /mnt/boot
root@ubuntu:~# for i in /dev /dev/pts /proc /sys /run; do mount -B $i /mnt$i; done