Steps I do when extending or resizing a VM disk in Proxmox

Preq

Download the GParted ISO.

Steps

Go to storage on main node or node you are working on. In my case it's local (server).

server is the node.

Go to ISO Images tab. The UI would looks like this.

Cause i have some ISO had uploaded before, then that's way you are see there are some ones.

Click an button Upload then select the ISO file, then click the Upload button at bottom, then wait until uploading process it's finish.

Select the VM you are working on. In my case 103 (debian). Go to Hardware tab.

Find CD/DVD Drive then click the Edit button. You are see the popup occur. Select the ISO file (gparted) then click OK.

Then go to Options tab.

Double click Boot Order then reorder to make the CD/DVD Drive it's on top, then click OK.

After that, you can do shutdown then start again the VM. It will bot the GParted. The next step just follow the process. Till the GUI it's occur. You can basically doing same thing like in Windows, which just drag and drop till the root (/) partition it's filling up with the free space. After everything it's done. You can go back change the boot to like before do, then doing shutdown and start again.

Swap partition

If you was remove the swap partition like i did, here is what i do.

Find the new UUID

sudo blkid

It does display information about all block devices include the UUID.

Change the UUID in /etc/fstab

sudoedit /etc/fstab

Following your $EDITOR, by default it will use nano

Enable swap

sudo swapon -a

-a it will scan swap things in /etc/fstab

Verify

Maybe you want to see it's swap it's active and the root (/) partition it's basically filling up.

df -h  # Check root partition size
free -h  # Check swap is active