How to grow the disk of an EC2 machine without reinstalling anything

In EC2 the disk is not tied to the size of the machine: it can be enlarged whenever you want, even with the machine running, without reinstalling or moving anything. There are two parts: telling AWS the disk is bigger, and telling the operating system inside to make use of it. The first is one click; the second, two commands that are scary the first time and then get typed from memory.

The only thing you can't do is shrink: a disk only grows. So grow it sensibly.

Step by step

1. Take a snapshot first

   EC2 console, Volumes menu, select the machine's disk (the "Attached to" column tells you which one), Actions, Create snapshot. It is the safety net; in practice the process is safe, but it costs nothing... well, a few cents of storage.

2. Grow the volume from the console

   With the volume selected, Actions, Modify volume. Enter the new size in GB (for example from 20 to 40) and, if the type is gp2, take the chance to change it to gp3. Modify. The volume state goes to "modifying" and then "optimizing"; you don't need to wait for the optimisation to finish before going on; as soon as the new size appears in the list you can continue. Bear in mind that AWS only lets you modify a volume once every six hours.

3. See how the disk looks from inside

   Connect to the machine via SSH and type:

   lsblk
   df -h /

   The first command shows the disk (xvda or nvme0n1) already at the new size, and below it its partition (xvda1 or nvme0n1p1) still at the old size. The second shows how much space the system sees: the old amount. Write down the exact names of the disk and partition.

4. Grow the partition

   sudo growpart /dev/xvda 1

   Mind the syntax: the disk, a space, and the partition number. With NVMe disks it would be sudo growpart /dev/nvme0n1 1. If it says growpart doesn't exist, install it (sudo apt install cloud-guest-utils on Ubuntu/Debian). Run lsblk again: the partition now fills the whole disk.

5. Grow the file system

   It depends on the type, which df -T / tells you. If it is ext4 (Ubuntu, Debian):

   sudo resize2fs /dev/xvda1

   If it is xfs (Amazon Linux, Red Hat):

   sudo xfs_growfs -d /

   Both work with the disk in use, without rebooting. Check with df -h /: the system now sees the new size.

6. If the disk is not the root one

   For an additional data disk, steps 4 and 5 are the same with the device name changed. If the disk has no partition (you formatted it directly on /dev/xvdf), skip growpart and run resize2fs /dev/xvdf or xfs_growfs on its mount point directly.

What can go wrong