Expand Linux VM Disk under Proxmox VE

Coauthored with GitHub Copilot and Claude

Posted on January 12, 2024

Updated: 30-Jan-2025

Sources:

Overview

This guide covers expanding disk space for Linux VMs running on Proxmox VE with ext4 filesystems. The process differs depending on whether your guest uses LVM (common with Ubuntu Server installs) or partitions directly.

Step 0: Identify Your Disk Setup

Check your setup inside the guest VM with lsblk. If you see lvm in the TYPE column, follow the With LVM section. Otherwise, follow the Without LVM section.

For example, with LVM:

# use the grep to hide loop devices
❯ lsblk | grep -e vda -e vg
vda                       253:0    0    97G  0 disk
├─vda1                    253:1    0     1M  0 part
├─vda2                    253:2    0     1G  0 part /boot
└─vda3                    253:3    0    96G  0 part
  └─ubuntu--vg-ubuntu--lv 252:0    0    96G  0 lvm  /

Now is a good time to also run df -h to see current filesystem sizes and sudo vgdisplay to see volume group details. We’ll revisit these later.

Step 1: Expand the Virtual Disk in Proxmox

On the Proxmox host, expand the VM’s disk:

qm resize <vmid> <disk> +<size>
# Example: add 10GB to VM 100's first virtio disk
qm resize 100 virtio0 +10G

Or use the GUI: VM → Hardware → Hard Disk → Resize.

Step 2: Rescan the Disk Inside the Guest

The guest OS needs to detect the new disk size:

# For virtio disks (vda)
echo 1 > /sys/class/block/vda/device/rescan

# For SCSI disks (sda)
echo 1 > /sys/class/block/sda/device/rescan

Verify the new size with the lsblk command from above and confirm the disk size increased.

With LVM (Ubuntu Server Default)

Typical layout:

NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
vda                       252:0    0   77G  0 disk
├─vda1                    252:1    0    1M  0 part
├─vda2                    252:2    0    2G  0 part /boot
└─vda3                    252:3    0   75G  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0   65G  0 lvm  /

Step 3a: Expand the Partition

Resize the partition containing the LVM physical volume (usually partition 3):

parted /dev/vda resizepart 3 100%

Or interactively:

parted /dev/vda
(parted) print        # confirm partition numbers
(parted) resizepart 3 100%
(parted) quit

Step 4a: Resize the LVM Physical Volume

pvresize /dev/vda3

Verify free space appeared in the volume group:

vgdisplay

Step 5a: Extend the Logical Volume

Use all available space:

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

Or add a specific amount:

lvextend -L +10G /dev/ubuntu-vg/ubuntu-lv

Step 6a: Resize the Filesystem

resize2fs /dev/ubuntu-vg/ubuntu-lv

Without LVM (Direct Partition)

Typical layout:

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
vda    252:0    0   50G  0 disk
├─vda1 252:1    0  512M  0 part /boot/efi
└─vda2 252:2    0 49.5G  0 part /

Step 3b: Expand the Partition

Use growpart (from cloud-guest-utils) to expand the root partition:

growpart /dev/vda 2

Or with parted:

parted /dev/vda resizepart 2 100%

Step 4b: Resize the Filesystem

resize2fs /dev/vda2

Verify the Changes

df -h
lsblk

Your root filesystem should now show the expanded size.

Notes

  • Always back up important data before resizing.
  • Shrinking disks is risky and not covered here.
  • A reboot may be required if the kernel doesn’t recognize changes.
Tags: linux proxmox