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Module 1 · Lesson 3 25 min Free lesson

Snapshots, Updates and Safe Rollback

Goal

Update your practice machine, take snapshots before risky work, and restore a snapshot to undo a change.

Before you start

Lesson 2 - a working Ubuntu Server 24.04 VM you can log in to.

A snapshot is an undo button for the whole machine

A snapshot saves the complete state of a VM's disk (and optionally its memory) at one moment. Restoring it puts the machine back exactly as it was - every file, setting and installed program.

That changes how you can learn: if a command in a later lesson breaks something, you do not need to repair it or reinstall. You restore the last snapshot and try again.

Where to find snapshots

SoftwareWhere
VirtualBoxSelect the VM → the menu (☰) next to its name → Snapshots → Take
UTMSnapshots are not in the main window in every version. Shut the VM down and duplicate it (right-click → Clone) as your restore point, or use the snapshot option if your UTM version shows one
Hyper-VRight-click the VM → Checkpoint
virt-managerOpen the VM → View → Snapshots → +

Taking a snapshot while the VM is shut down is the simplest and most reliable option. Give every snapshot a name that says what state it captures, for example 01-fresh-install or 02-updated.

Updating Ubuntu

Ubuntu installs software from package repositories with the apt tool (Module 5 explains it in depth). Updating is always two steps:

bash
sudo apt update
sudo apt upgrade
  • sudo apt update downloads the current list of available package versions. It does not change any software yet.
  • sudo apt upgrade installs the newer versions. It shows what it will do and asks Do you want to continue? [Y/n] - press Enter or Y.

If the kernel was updated, Ubuntu tells you a restart is required. You can check yourself:

bash
ls /var/run/reboot-required

If the file exists, restart:

bash
sudo reboot

If ls answers No such file or directory, no restart is needed.

Diagram: a timeline of snapshots 01-fresh-install, then apt update and upgrade, snapshot 02-updated, then an experiment that breaks something; restoring 02-updated returns the VM to the known good state. A note says snapshots are not backups
Snapshots are save points. Restore the last good one instead of repairing a broken experiment.

Trying a rollback

Let's prove the undo button works. Create a file in your home directory:

bash
echo "this file should disappear" > rollback-test.txt
ls

echo prints text, and > writes that text into a file (Module 3 explains this). ls now shows rollback-test.txt.

Shut down, restore the snapshot you took before creating the file, start the VM and log in again. Run ls - the file is gone.

Practice task

  1. Shut the VM down and take a snapshot named 01-fresh-install.
  2. Start it, log in and run sudo apt update and sudo apt upgrade. Reboot if /var/run/reboot-required exists.
  3. Shut down and take a snapshot named 02-updated.
  4. Start the VM, create rollback-test.txt as shown above and check it exists.
  5. Shut down, restore 02-updated, start the VM and confirm the file is gone.

Check your work

  • Your snapshot list shows 01-fresh-install and 02-updated.
  • After restoring 02-updated, ls no longer shows rollback-test.txt.
  • Running sudo apt update again ends with a line such as All packages are up to date.

Common mistakes:

  • Restoring the snapshot but not starting the VM again from it (some tools ask whether to keep the current state - choose to restore).
  • Running apt upgrade without apt update first - you get the versions from an old list.
  • Typing apt update without sudo - you get a Permission denied error because only administrators may change software.
Show the solution - try the task first
text
anna@lab:~$ sudo apt update
[sudo] password for anna:
...
Reading package lists... Done
Building dependency tree... Done
5 packages can be upgraded. Run 'apt list --upgradable' to see them.
anna@lab:~$ sudo apt upgrade
...
Do you want to continue? [Y/n] y
...
anna@lab:~$ ls /var/run/reboot-required
ls: cannot access '/var/run/reboot-required': No such file or directory

The number of packages and the exact output will differ. After restoring 02-updated:

text
anna@lab:~$ ls
anna@lab:~$

An empty result means your home directory contains no visible files - the test file is gone.

In short

Snapshots let you undo anything on your practice machine, but they are not backups. Before updates or experiments, take a named snapshot. Update Ubuntu with sudo apt update followed by sudo apt upgrade, and reboot when /var/run/reboot-required exists.

Look it up later

Reference pages for what this lesson uses - handy when you need a reminder.

Commands

apt sudo ls echo

Key terms

Virtual Machine (VM) Kernel

Cheat sheets

Quick quiz

3 questions · pass mark 80% · every answer is explained

1. What does sudo apt update do?
2. Is a VM snapshot a backup?
3. When is a restart needed after updating Ubuntu?

Log in to save your quiz results.

Go deeper

Dargslan books that cover this topic in more depth.

Linux Patch Management & System Updates Linux Backup Strategies Ubuntu Server Administration

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