Extending an LVM Root Filesystem on a Proxmox Guest VM

  • July 17, 2026
  • del

A short reference for when a Linux VM running under Proxmox runs out of disk space. This assumes the guest was set up with LVM (the common default for Debian/Ubuntu installs) and that you’ve already grown the virtual disk in the Proxmox UI.

Step 0 — Grow the disk in Proxmox

Select the VM, go to Hardware, select the disk, and use Disk Action → Resize to add space. This only enlarges the virtual disk; the guest OS still needs to be told to use the new space.

Step 1 — Check the current layout (inside the guest)

lsblk
df -hT /
sudo vgs
sudo lvs

Note your disk (e.g. /dev/sda), the partition number, and the logical volume path (e.g. /dev/ubuntu-vg/ubuntu-lv). Adjust the commands below to match your own output.

Step 2 — Grow the partition

sudo growpart /dev/sda 3

If growpart isn’t installed, grab it from cloud-guest-utils (Debian/Ubuntu) or cloud-utils-growpart (RHEL). If the kernel doesn’t see the larger disk yet, a reboot or a SCSI rescan will sort it out.

Step 3 — Resize the LVM physical volume

sudo pvresize /dev/sda3

Step 4 — Extend the logical volume

To use all of the newly available free space:

sudo lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv

Step 5 — Grow the filesystem

Check the filesystem type with df -hT /, then:

  • ext4: sudo resize2fs /dev/ubuntu-vg/ubuntu-lv
  • xfs: sudo xfs_growfs / (xfs grows by mount point, not device)

Tip: combine the last two steps

Steps 4 and 5 can be done in one go with the -r flag, which resizes the filesystem at the same time:

sudo lvextend -r -l +100%FREE /dev/ubuntu-vg/ubuntu-lv

Step 6 — Verify

df -h /

All of this works online — no unmount or downtime needed for ext4 or xfs root filesystems.

del