Root partition shrinking on a machine with no physical access

Question

Ok so let me try to explain it as thoroughly as possible. So I'm using chameleon cloud to reserve nodes on bare metal (~distant computers) and access them via ssh. These nodes run Ubuntu 20.04, and the ones I have access to only have 1 SSD, this is important as the project I am in requires only SSD's.

Root is on sda1 on the ssd, and sda1 occupies the whole ssd.

Basically I want to shrink sda1 (which contains root), to create another partition on the SSD and mount another filesystem for my project on it(this filesystem will change throughout the course of the project, btrfs, xfs, etc). So, the original EXT4 filesystem will stay on sda1, I need an extra partition with another filesystem. But since this is not a machine I have physical access to, I cannot use a usb stick or a CD to reinstall, etc.

I understand this might be confusing, maybe incorrect or incomplete. This is also probably not a new question, but I can't find satisfying answers that can adapt to my case. My project lead thinks that this is a solvable issue. Feel free to ask for more details (screenshots of commands, or whatever), correct errors, help me, anything is welcome.

I thank you very much for your time and help.

Answer 1

I did this in my Amazon Lightsail vps in order to convert it over to using LVM. First, you have to disable the cloud-init package from automatically growing the partition on each boot. IIRC, you need to comment out or delete the lines in /etc/cloud/cloud.cfg that reference growpart and resizefs. Then you can add these two scripts:

#!/bin/sh
PREREQ=""
prereqs()
{
        echo "$PREREQ"
}
case "${1:-}" in
  prereqs)
    prereqs
    exit 0
    ;;
esac
. /usr/share/initramfs-tools/hook-functions
copy the binary as early as possible
copy_exec /sbin/resize2fs /sbin
copy_exec /sbin/e2fsck /sbin

Put that in /etc/initramfs-tools/hooks/resize-hook

#!/bin/sh
PREREQ=""
prereqs()
{
        echo "$PREREQ"
}
case $1 in
get pre-requisites
prereqs)
        prereqs
        exit 0
        ;;
esac
e2fsck -fy /dev/sda1
resize2fs /dev/sda1 9g

Change the 9g to whatever size you want the fs shrunk to and put that in /etc/initramfs-tools/scripts/local-premount/resize. Don't forget to chmod the two scripts +x, and rebuild your initramfs with update-initramfs.

After you reboot, verify that the filesystem did get shrunk (df), use the resizepart command in parted to shrink the partition. It' a good idea to leave an extra gb or so in the partition to make sure you don't shrink the partition smaller than the filesystem, then run resize2fs on it later to expand it to fill the whole new partition size.

Also after you verify that the filesystem was shrunk, remove the two above scripts and rebuild your initramfs again.

Answer 2

Psusi's answer will work if performed correctly, but a small mistake could leave you with an unresponsive system. If that happens I believe you would lose anything you already have on your system. So if you chose that option you should take a snapshot first!

---

Reading into Chameleon cloud, it's built around the concept of images. You provision a server for some time, deploy an image to it and be careful to snapshot your server at the end of your lease or risk losing the lot. There are some hints on chameleon that most images are single partition inferring that some might not be.

If it were me I wouldn't edit the server in place. Instead I would download download the latest snapshot to my local machine (any linux or mac you have access to), edit it, upload it and then use it.

According to the documentation these images are QCOW2 images. Once downloaded these can be converted to a raw image with qemu-image convert. Modified with resize2fs / fdisk, repacked with qemu-image and uploaded back:

# Unpack
qemu-img convert -p -O raw base_image.qcow2 raw_image
Repack
qemu-img convert -p -O qcow2 raw_image new_image.qcow_2