Resizing a disk on Ubuntu live can be really useful when uptime is a necessity.

This guide covers two scenarios: a disk using LVM (Volume Groups) and a plain ext4 partition with no LVM. In both cases, assumes EXT4 as the filesystem type and that you've already added the space to the disk itself (e.g. via your hypervisor).

With LVM (Volume Group)

Before LVM can use the new space, the partition and physical volume need to know about it first.

Confirm Partitions:

fdisk -l

Disk /dev/vda: 10.86 TiB, 11940009082880 bytes, 23320330240 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt

Device       Start         End     Sectors  Size Type
/dev/vda1     2048        4095        2048    1M BIOS boot
/dev/vda2     4096     2101247     2097152    1G Linux filesystem
/dev/vda3  2101248 19025360895 19023259648  8.9T Linux filesystem


Disk /dev/mapper/ubuntu--vg-ubuntu--lv: 8.86 TiB, 9739907891200 bytes, 19023257600 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

/dev/vda3 is the target partition we want to expand.

First we need to resize the partition first, then the PV on top of it:

sudo growpart /dev/vda 3
# CHANGED: partition=3 start=2101248 old: size=19023259648 end=19025360896 new: size=23318228959 end=23320330207

sudo pvresize /dev/vda3
# Physical volume "/dev/vda3" changed
# 1 physical volume(s) resized or updated / 0 physical volume(s) not resized

Now extend the logical volume and resize the filesystem:

sudo lvextend -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
sudo resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv

That's it! No reboot needed.

Without LVM (Plain ext4)

If your disk has no LVM — just a partition directly formatted as ext4 — the process is simpler. A layout like this is common on VMs provisioned without LVM:

Device       Start        End    Sectors   Size Type
/dev/sda1     2048    2203647    2201600     1G EFI System
/dev/sda2  2203648 1048575966 1046372319 498.9G Linux filesystem

After expanding the disk in your hypervisor, rescan the SCSI bus so the kernel picks up the new size:

echo 1 > /sys/class/block/sda/device/rescan

Confirm the kernel sees the expanded disk:

fdisk -l /dev/sda

Grow the partition, then resize the filesystem directly:

sudo growpart /dev/sda 2
sudo resize2fs /dev/sda2

resize2fs supports online resizing of mounted ext4 filesystems, so no unmounting or rebooting is needed. Verify the result:

df -h /

That's it! No reboot needed.