Expanding a Proxmox VM Disk on Debian

This post was generated largely by AI based on my notes.

1. Check the current layout

See how the disk and partitions are structured:

lsblk -o NAME,FSTYPE,SIZE,MOUNTPOINT,TYPE
sudo fdisk -l /dev/sda

If you resized the disk in Proxmox, it shows a larger size for /dev/sda but partitions still reflect the old size.

2. Fix the GPT table

gdisk corrects the GPT header so it matches the new disk size.

sudo gdisk /dev/sda

Type w and confirm with y. This writes the corrected GPT to disk.

3. Reload partition table

Tell the kernel to reload the partition layout:

sudo partx -u /dev/sda

If partx is missing, you can install util-linux or just reboot.

4. Expand the root partition

growpart automatically extends partition 1 to fill all remaining space.

sudo growpart /dev/sda 1

The output should confirm that partition 1 has grown.

5. Resize the filesystem

Extend the ext4 filesystem to fill the new partition size:

sudo resize2fs /dev/sda1

This can be done online while mounted.

6. Verify everything

Check the new size and ensure all space is available:

df -h /

You should now see your full expanded disk space in use.

To confirm integrity:

sudo gdisk -l /dev/sda && sudo e2fsck -n /dev/sda1

Both should report clean results.

The Debian root filesystem now uses the entire expanded Proxmox disk.