Right, I should have thought of that. Thank you.
Here's the output now:
root@xubuntu:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdb 8:16 1 7.5G 0 disk /cdrom
└─sdb1 8:17 1 1.2G 0 part
loop0 7:0 0 1.2G 1 loop /rofs
sda 8:0 0 55.9G 0 disk
├─sda2 8:2 0 1K 0 part
├─sda5 8:5 0 55.4G 0 part
└─sda1 8:1 0 487M 0 part
root@xubuntu:~# pvdisplay
root@xubuntu:~# vgdisplay
root@xubuntu:~# cryptsetup luksOpen /dev/sda5 root
Enter passphrase for /dev/sda5:
root@xubuntu:~#
root@xubuntu:~# sudo mke2fs -n /dev/sda5
mke2fs 1.42.13 (17-May-2015)
/dev/sda5 contains a crypto_LUKS file system
Proceed anyway? (y,n) y
/dev/sda5 is apparently in use by the system; will not make a filesystem
here!
root@xubuntu:~# umount /dev/sda
umount: /dev/sda: not mounted
root@xubuntu:~# umount /dev/sda5
umount: /dev/sda5: not mounted
root@xubuntu:~#
