First you need to increase the size of the disk being presented to the Linux OS. This is most likely done by expanding the virtual disk in KVM/VMWare/Hyper-V or by adjusting your RAID controller / storage system to increase the volume size. You can often do this while Linux is running; without shutting down or restarting. I’ve extended my 100GB disk to 200GB for my example machine.

Once that is done, you may need to get Linux to rescan the disk for the new free space. Check for free space by running cfdisk and see if there is free space listed, use “q” to exit once you’re done.

Linux increase disk size space cfdisk

If you don’t see free space listed, then initiate a rescan of /dev/sda with echo 1>/sys/class/block/sda/device/rescan. Once done, rerun cfdisk and you should see the free space listed.

Linux free partition space scan

Select your /dev/sda3 partition from the list and then select “Resize” from the bottom menu. Hit ENTER and it will prompt you to confirm the new size. Hit ENTER again and you will now see the /dev/sda3 partition with a new larger size.

Select “Write” from the bottom menu, type yes to confirm, and hit ENTER. Then use “q” to exit the program.

Now that the LVM partition backing the /dev/sda3 Physical Volume (PV) has been extended, we need to extend the PV itself. Run pvresize /dev/sda3 to do this and then use pvdisplay to check the new size.

Ubuntu extend physical volume pvresize

As you can see above, my PV has been increased from 98.5GB to 198.5GB. Now let’s check the Volume Group (VG) free space with vgdisplay.

Ubuntu LVM: check vg space vgdisplay

We can see above that the VG has 100GB of free space. Now let’s check the size of our upstream Logical Volume (LV) using lvdisplay, extend the LV to use up all the VG’s free space with lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv, and then check the LV one more time with lvdisplay to make sure it has been extended.

Ubuntu LVM: check LV size lvdisplay

At this point, the block volume underpinning our root filesystem has been extended, but the filesystem itself has not been resized to fit that new volume. To do this, run df -h to check the current size of the file system, then run resize2fs /dev/mapper/ubuntu–vg-ubuntu–lv to resize it, and df -h one more time to check the new file system available space.

Ubuntu LVM: extend filesystem resize2fs

And there you go. You’ve now taken an expanded physical (or virtual) disk and moved that free space all the way up through the LVM abstraction layers to be used by your (critically full) root file system. Time to check it off the to-do list and move on to the next IT emergency.