HOWTO Easily Resize the Default LVM Volume on Ubuntu 18.04

05 Saturday Dec 2020

Say you have a 40 Gig disk. When the installer creates the encrypted volume during initial OS installation, it partitions the whole disk but only creates a 20 GB logical volume. You should resize the default volume group to increase the usable disk from 20 to 40 GB.

1) You will run a test first to verify that it can resize properly before you actually modify the partition.
a. Change to root and gather a few details. Points of interest are in bold red. You can see that the partition (type=part) for sda3 is 39G and the logical volume (type=lvm) is only 20 G.
> sudo -s (or su – root)
> lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 89.1M 1 loop /snap/core/8268
loop1 7:1 0 96.5M 1 loop /snap/core/9436
sda 8:0 0 40G 0 disk
├─sda1 8:1 0 1M 0 part
├─sda2 8:2 0 1G 0 part /boot
└─sda3 8:3 0 39G 0 part
└─dm_crypt-0 253:0 0 39G 0 crypt
└─ubuntu–vg-ubuntu–lv 253:1 0 20G 0 lvm /
sr0 11:0 1 1024M 0 rom

> df -h | grep “ubuntu–vg-ubuntu–lv”

/dev/mapper/ubuntu–vg-ubuntu–lv 20G 15G 4.0G 79% /

b. Now that we know the logical volume is only 20 Gigs, we can resize it to the remaining open free space. First, we will test this command using the -t switch (for test) and view the output for errors. If clean, proceed.
> lvresize -t -v -l +100%FREE /dev/mapper/ubuntu–vg-ubuntu–lv

TEST MODE: Metadata will NOT be updated and volumes will not be (de)activated.
Converted 100%FREE into at most 4862 physical extents.
Test mode: Skipping archiving of volume group.
Extending logical volume ubuntu-vg/ubuntu-lv to up to 38.99 GiB
Size of logical volume ubuntu-vg/ubuntu-lv changed from 20.00 GiB (5120 extents) to 38.99 GiB (9982 extents).
Test mode: Skipping backup of volume group.
Logical volume ubuntu-vg/ubuntu-lv successfully resized.
Test mode: Wiping internal cache
Wiping internal VG cache

2) Once you see that the test was successful, remove the -t switch (for test) from the previous command to actually increase the logical volume.
> lvresize -v -l +100%FREE /dev/mapper/ubuntu–vg-ubuntu–lv

Converted 100%FREE into at most 4862 physical extents.
Archiving volume group “ubuntu-vg” metadata (seqno 2).
Extending logical volume ubuntu-vg/ubuntu-lv to up to 38.99 GiB
Size of logical volume ubuntu-vg/ubuntu-lv changed from 20.00 GiB (5120 extents) to 38.99 GiB (9982 extents).
Loading ubuntu–vg-ubuntu–lv table (253:1)
Suspending ubuntu–vg-ubuntu–lv (253:1) with device flush
Resuming ubuntu–vg-ubuntu–lv (253:1)
Creating volume group backup “/etc/lvm/backup/ubuntu-vg” (seqno 3).
Logical volume ubuntu-vg/ubuntu-lv successfully resized.

> lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 89.1M 1 loop /snap/core/8268
loop1 7:1 0 96.5M 1 loop /snap/core/9436
sda 8:0 0 40G 0 disk
├─sda1 8:1 0 1M 0 part
├─sda2 8:2 0 1G 0 part /boot
└─sda3 8:3 0 39G 0 part
└─dm_crypt-0 253:0 0 39G 0 crypt
└─ubuntu–vg-ubuntu–lv 253:1 0 39G 0 lvm /
sr0 11:0 1 1024M 0 rom

3) Now that the logical volume is 39G, get the FS type and resize the filesystem on the newly acquired space. We can see that it’s using ext4.
> df -h -T |grep vg
/dev/mapper/ubuntu–vg-ubuntu–lv ext4 20G 15G 4.0G 79% /

a. Since the file system is ext4, we will use the resize2fs command.
> resize2fs -p /dev/mapper/ubuntu–vg-ubuntu–lv

resize2fs 1.44.1 (24-Mar-2018)
Filesystem at /dev/mapper/ubuntu–vg-ubuntu–lv is mounted on /; on-line resizing required
old_desc_blocks = 3, new_desc_blocks = 5
The filesystem on /dev/mapper/ubuntu–vg-ubuntu–lv is now 10221568 (4k) blocks long.

b. Now verify the new size of your root volume to confirm that it has increased in size.
> df -h -T |grep vg
/dev/mapper/ubuntu–vg-ubuntu–lv ext4 39G 15G 22G 41% /