How to resize a LUKS encrypted root partion

The Ubuntu standard setup for an encrypted root file system is quite complex as the following output shows:

root@ephiphany~# lsblk
NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
vda                 252:0    0     1T  0 disk
├─vda1              252:1    0     1M  0 part
├─vda2              252:2    0     1G  0 part  /boot
└─vda3              252:3    0  1024G  0 part
  └─dm_crypt-3      253:0    0  1024G  0 crypt
    └─epiphany-root 253:1    0  1024G  0 lvm   /

Basically we have a disk (vda) with the root partition on the vda3 partion which holds the encrpyted LUKS device which is decrypted as dm_crypt-3. On top of dm_crypt-3 we have a physical LVM volume with volume group epiphany and the logical volume root.

Consequently, growing the root filesystem requires:

1. extending the vda3 paritition which is done using fdisk (please refer to a the the following guideline for more information)
2. resizing the LUKS parition
3. resizing the physical device,
4. resizing the logical device, and finally
5. growing the file system

as outlined below:

# resize the LUKS parititon (dm_crypt-3)
cryptsetup resize dm_crypt-3

# resize the physical device on top of it
pvresize /dev/mapper/dm_crypt-3 

# resize the logical device (epiphany-root)
lvextend -l +100%FREE /dev/mapper/epiphany-root

# grow the file system accordingly
resize2fs /dev/mapper/epiphany-root