Use Btrfs for Root Level Snapshots on Oracle Linux

Introduction

As with any operating system, you must apply patches to keep it current and secure. But what if something goes wrong with an update or system files get deleted? Having a process in place to perform a restore is vital.

While you may be familiar with traditional backup and restore, you gain additional options when using Btrfs as your root file system. Using Btrfs requires booting into Oracle’s Unbreakable Enterprise Kernel (UEK) release and provides the option to create Btrfs snapshots, and use Snapper to automate, manage, and recover snapshots.

This tutorial describes how to perform a backup and restore using Btrfs snapshot and Snapper to recover from a system failure.

Objectives

In this tutorial, you will learn how to:

• Verify you’re running a Btrfs root file system
• Create a snapshot with Btrfs
• Install and configure Snapper
• Use Snapper to manage snapshots
• Rollback system changes

Prerequisites

• Minimum of a single Oracle Linux system running the UEK kernel

• Each system should have Oracle Linux installed and configured with:

  • A non-root user account with sudo access
  • Access to the Internet
  • Btrfs root file system

Verify the Root File System

To continue with the steps in this tutorial, the root file system of the Oracle Linux installation should be using Btrfs.

1. Get the Btrfs volume label.

   sudo btrfs filesystem show
   

   Example Output:

   Label: 'ol'  uuid: 8489558b-4458-45de-b167-78f0b264d10b
   	Total devices 1 FS bytes used 4.91GiB
   	devid    1 size 20.00GiB used 8.02GiB path /dev/vda1
   

2. List the block devices.

   lsblk -p /dev/vda
   

   Where /dev/vda matches the device associated with the Btrfs volume label.

   Example Output:

   NAME        MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
   /dev/vda    252:0    0  20G  0 disk 
   └─/dev/vda1 252:1    0  20G  0 part /boot
                                       /home
                                       /
   

3. List the Btrfs subvolumes.

   sudo btrfs subvolume list /
   

   Example Output:

   ID 256 gen 39 top level 5 path boot
   ID 257 gen 75 top level 5 path root
   ID 258 gen 71 top level 5 path home
   

Install and Configure Snapper

Snapper is a utility that manages Btrfs snapshots. It allows snapshot creation and deletion while enabling users to compare snapshot differences and revert changes at the file level.

1. Install Snapper.

   sudo dnf install -y python3-dnf-plugin-snapper
   

   The DNF plugin allows creating pre and post snapshots every time you install a package.

2. Create a Snapper configuration file for each subvolume.

   sudo snapper -c root create-config /
   sudo snapper -c home create-config /home
   

   The create-config option adds a subvolume entry into the /etc/sysconfig/snapper file, generates a configuration file under /etc/snapper/configs/ based on the -c option, and places a .snapshots directory in the specified subvolume for the snapper-generated snapshots.

3. Show a listing of the Snapper configurations.

   sudo snapper list-configs
   

   Example Output:

   Config | Subvolume
   -------+----------
   home   | /home    
   root   | /   
   

4. View the root Snapper configuration.

   sudo cat /etc/snapper/configs/root
   

5. Add the snapshot subvolumes to the /etc/fstab file.

   1. Get the UUID of the Btrfs system root.

      ROOT_UUID="$(sudo grub2-probe --target=fs_uuid /)"
      

   2. Add the subvolumes to the /etc/fstab file.

      echo "UUID=${ROOT_UUID} /.snapshots         btrfs subvol=root/.snapshots 0 0" | sudo tee -a /etc/fstab > /dev/null
      echo "UUID=${ROOT_UUID} /home/.snapshots    btrfs subvol=home/.snapshots 0 0" | sudo tee -a /etc/fstab > /dev/null
      

   3. Reload the /etc/fstab file.

      sudo systemctl daemon-reload
      sudo mount -va
      

Create and List Snapshots

1. Get a list of subvolumes.

   sudo btrfs subvolume list /
   

   Example Output:

   ID 256 gen 42 top level 5 path boot
   ID 257 gen 52 top level 5 path root
   ID 258 gen 51 top level 5 path home
   ID 259 gen 51 top level 257 path .snapshots
   ID 260 gen 52 top level 258 path home/.snapshots
   

2. Create your first snapshot.

   sudo btrfs subvolume snapshot / /.snapshots/root
   

   • /: is the source
   • /.snapshots/: is the destination
   • root: is the name

   If you don’t provide a name, Btrfs will use the name of the source subvolume. In our case, the name of the source subvolume is / , which is not a valid name for the snapshot.

3. Display the current snapshot and its size.

   sudo btrfs filesystem du -s /
   

   Example Output:

     Total   Exclusive  Set shared  Filename
   9.20GiB   329.38MiB     4.44GiB  /
   

4. Test the Snapper DNF plugin.

   The plugin automatically creates a pre and a post snapshot surrounding the dnf command.

   sudo dnf install -y git
   

5. View the list of available snapshots.

   sudo snapper -c root list
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup | Description             | Userdata
   ---+--------+-------+---------------------------------+------+---------+-------------------------+---------
   0  | single |       |                                 | root |         | current                 |         
   1  | pre    |       | Thu 08 Aug 2024 07:00:25 PM EDT | root | number  | /bin/dnf install git -y |         
   2  | post   |     2 | Thu 08 Aug 2024 07:00:28 PM EDT | root | number  | /bin/dnf install git -y |         
   

   Note: Snapper does not display snapshots created directly using btrfs, such as our first snapshot.

6. Create a snapshot using Snapper.

   sudo snapper -c root create --description "next snapshot"
   

7. Get a list of snapshots.

   sudo snapper -c root list
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup | Description             | Userdata
   ---+--------+-------+---------------------------------+------+---------+-------------------------+---------
   0  | single |       |                                 | root |         | current                 |         
   1  | pre    |       | Thu 08 Aug 2024 07:00:25 PM EDT | root | number  | /bin/dnf install git -y |         
   2  | post   |     1 | Thu 08 Aug 2024 07:00:28 PM EDT | root | number  | /bin/dnf install git -y |         
   3  | single |       | Thu 08 Aug 2024 07:03:38 PM EDT | root |         | next snapshot           |         
   

Enable Automatic Snapper Snapshots.

Each snapper configuration contains settings for a periodic backup, controlled by the TIMELINE_CREATE configuration variable. The TIMER settings, which control the snapper systemd timer unit, trigger automatic snapshots. The Snapper timer configuration keeps ten hourly, ten daily, ten monthly, and ten yearly snapshots by default and uses the TIMELINE_LIMIT values to prune the number of snapshots during cleanup. See the man snapper-configs for more information.

1. Start the Snapper timeline timer unit.

   sudo systemctl enable --now snapper-timeline.timer
   

   A single snapshot will appear every hour going forward.

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup  | Description                      | Userdata
   ---+--------+-------+---------------------------------+------+----------+----------------------------------+---------
   ...
   4  | single |       | Thu 08 Aug 2024 09:00:07 PM EDT | root | timeline | timeline                         |         
   

2. Start the Snapper cleanup timer unit.

   sudo systemctl enable --now snapper-cleanup.timer
   

   This second systemd timer unit handles the pruning of stale snapshots so that your snapshots remain manageable.

Test Snapper

These tests will verify that Snapper is working correctly and has no issues.

Rollback a DNF package

Earlier in the tutorial, we installed the git package and its dependencies. Now, we’ll attempt to undo those changes.

1. Verify git exists on the system.

   git --version
   

2. Check Snapper for snapshots.

   sudo snapper ls
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup | Description             | Userdata
   ---+--------+-------+---------------------------------+------+---------+-------------------------+---------
   0  | single |       |                                 | root |         | current                 |         
   1  | pre    |       | Thu 08 Aug 2024 08:22:15 PM EDT | root | number  | /bin/dnf install -y git |         
   2  | post   |     1 | Thu 08 Aug 2024 08:22:17 PM EDT | root | number  | /bin/dnf install -y git |         
   3  | single |       | Thu 08 Aug 2024 08:24:14 PM EDT | root |         | next snapshot           |     
   

   The git package is part of the pre (#1) and post (#2) snapshots.

3. Show the changes between the snapshots.

   sudo snapper status 1..2
   

   The output shows the files and directories that the installation steps create (+), modify (c), or delete (-) between the pre and post snapshots.

4. Undo the changes.

   sudo snapper undochange 1..2
   

   Example Output:

   create:1 modify:14 delete:1623
   

5. Verify the removal of git.

   which git
   

   The output reports no git found.

6. Now revert the undo changes.

   sudo snapper undochange 2..1
   

   You should now be able to rerun the command git --version.

Undo File Changes

What happens when you make configuration changes and realize you need to undo them? Snapper allows you to make changes to individual files.

1. Show the contents of your /etc/hosts file.

   cat /etc/hosts
   

   Example Output:

   127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
   ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
   

2. Add a line to the /etc/hosts file.

   echo "192.168.10.4 ol-btrfs-root" | sudo tee -a /etc/hosts > /dev/null 
   

3. Compare the changes in the /etc/hosts file with the one in snapshot #3.

   sudo snapper diff 3..0 /etc/hosts
   

   Example Output:

   --- /.snapshots/3/snapshot/etc/hosts	2020-06-23 02:11:43.000000000 -0400
   +++ /etc/hosts	2024-08-08 21:04:45.092838646 -0400
   @@ -1,2 +1,3 @@
    127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
    ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
   +192.168.10.4 ol-btrfs-root
   

   The output shows the last line added to the /etc/hosts file since snapshot #3.

4. Roll back the changes.

   sudo snapper undochange 3..0 /etc/hosts
   

5. Verify the rollback of the changes.

   cat /etc/hosts
   

   Example Output:

   127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
   ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
   

Manually Create Pre-Post Snapshots

Imagine you want to roll back a series of commands or a product build. Here, we manually create pre snapshots of the / and /home directories and then undo all the changes when we finish our test.

1. Create the pre snapshots.

   sudo snapper -c root create -t pre -c number -d 'Pre Ansible'
   sudo snapper -c home create -t pre -c number -d 'Pre Ansible'
   

2. List the snapshots.

   sudo snapper ls
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup  | Description                      | Userdata
   ---+--------+-------+---------------------------------+------+----------+----------------------------------+---------
   0  | single |       |                                 | root |          | current                          |         
   1  | pre    |       | Thu 08 Aug 2024 08:22:15 PM EDT | root | number   | /bin/dnf install -y git          |         
   2  | post   |     1 | Thu 08 Aug 2024 08:22:17 PM EDT | root | number   | /bin/dnf install -y git          |         
   3  | single |       | Thu 08 Aug 2024 08:24:14 PM EDT | root |          | next snapshot                    |         
   4  | single |       | Thu 08 Aug 2024 09:00:07 PM EDT | root | timeline | timeline                         |         
   5  | pre    |       | Thu 08 Aug 2024 09:20:36 PM EDT | root | number   | Pre Ansible                      |         
   

   sudo snapper -c home ls
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup  | Description  | Userdata
   ---+--------+-------+---------------------------------+------+----------+--------------+---------
   0  | single |       |                                 | root |          | current      |         
   1  | single |       | Thu 08 Aug 2024 09:00:07 PM EDT | root | timeline | timeline     |         
   2  | pre    |       | Thu 08 Aug 2024 09:20:49 PM EDT | root | number   | Pre Ansible  |         
   

3. Install the Ansible package.

   sudo dnf install -y ansible-core
   

4. Run a sample playbook

   git clone https://github.com/oracle-devrel/linux-virt-labs.git
   cd linux-virt-labs/labs
   ansible-playbook olam-hello-world.yaml
   

   The Hello! Welcome to Oracle Linux Automation Manager. message will be displayed.

5. Create the post snapshots.

   sudo snapper -c root create -t post --pre-number 5 -c number -d 'Post Ansible'
   sudo snapper -c root create -t post --pre-number 2 -c number -d 'Post Ansible'
   

6. List the snapshots.

   sudo snapper -c root ls
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup  | Description                      | Userdata
   ---+--------+-------+---------------------------------+------+----------+----------------------------------+---------
   0  | single |       |                                 | root |          | current                          |         
   1  | pre    |       | Thu 08 Aug 2024 08:22:15 PM EDT | root | number   | /bin/dnf install -y git          |         
   2  | post   |     1 | Thu 08 Aug 2024 08:22:17 PM EDT | root | number   | /bin/dnf install -y git          |         
   3  | single |       | Thu 08 Aug 2024 08:24:14 PM EDT | root |          | next snapshot                    |         
   4  | single |       | Thu 08 Aug 2024 09:00:07 PM EDT | root | timeline | timeline                         |         
   5  | pre    |       | Thu 08 Aug 2024 09:20:36 PM EDT | root | number   | Pre Ansible                      |         
   6  | pre    |       | Thu 08 Aug 2024 09:21:41 PM EDT | root | number   | /bin/dnf install ansible-core -y |         
   7  | post   |     6 | Thu 08 Aug 2024 09:21:43 PM EDT | root | number   | /bin/dnf install ansible-core -y |         
   8  | post   |     5 | Thu 08 Aug 2024 09:25:45 PM EDT | root | number   | Post Ansible                     |         
   

   sudo snapper -c home ls
   

   Example Output:

    # | Type   | Pre # | Date                            | User | Cleanup  | Description  | Userdata
   ---+--------+-------+---------------------------------+------+----------+--------------+---------
   0  | single |       |                                 | root |          | current      |         
   1  | single |       | Thu 08 Aug 2024 09:00:07 PM EDT | root | timeline | timeline     |         
   2  | pre    |       | Thu 08 Aug 2024 09:20:49 PM EDT | root | number   | Pre Ansible  |         
   3  | post   |     2 | Thu 08 Aug 2024 09:26:53 PM EDT | root | number   | Post Ansible |      
   

7. Get a count of the number of changes made.

   sudo snapper -c root status 5..8 | wc -l
   

   sudo snapper -c home status 2..3 | wc -l
   

   The output shows the number of root and home file system changes.

8. Undo the changes.

   sudo snapper -c root undochange 5..8
   

   sudo snapper -c home undochange 2..3
   

   The undochange removes the Ansible package and the Git repository from the system as if we never ran the steps.

9. Verify the undo by trying to run ansible --version and getting a directory listing under your home directory.

   ansible --version
   

   Example Output:

   -bash: /usr/bin/ansible-playbook: No such file or directory
   

   ls ~
   

   The linux-virt-labs directory containing the Git repository no longer exists.

Set a Snapshot as the System Root

While the DNF plugin should handle package rollback due to failures, it does not handle a rogue script that does an rm on a critical directory. In that case, it would be good to have the ability to rollback before it happened or have had the foresight to wrap the script in a pre and post snapshot using the --command option.

Since time travel is impossible, let’s look at the rollback solution.

By making a subvolume snapshot of the main volume the default, you can easily roll back using the snapper tool without having to specify the snapshot number and the ‘ambit’ during the rollback.

1. Get a list of the subvolumes.

   sudo btrfs subvolume list /
   

   Example Output:

   ID 256 gen 60 top level 5 path boot
   ID 257 gen 153 top level 5 path root
   ID 258 gen 137 top level 5 path home
   ID 259 gen 146 top level 257 path .snapshots
   ID 260 gen 139 top level 258 path home/.snapshots
   ID 261 gen 60 top level 259 path .snapshots/root
   ID 262 gen 67 top level 259 path .snapshots/1/snapshot
   ID 263 gen 69 top level 259 path .snapshots/2/snapshot
   ID 264 gen 73 top level 259 path .snapshots/3/snapshot
   ID 265 gen 91 top level 260 path home/.snapshots/1/snapshot
   ID 266 gen 92 top level 259 path .snapshots/4/snapshot
   ID 267 gen 105 top level 259 path .snapshots/5/snapshot
   ID 268 gen 106 top level 260 path home/.snapshots/2/snapshot
   ID 269 gen 108 top level 259 path .snapshots/6/snapshot
   ID 270 gen 110 top level 259 path .snapshots/7/snapshot
   ID 271 gen 117 top level 259 path .snapshots/8/snapshot
   ID 272 gen 120 top level 260 path home/.snapshots/3/snapshot
   ID 273 gen 138 top level 260 path home/.snapshots/4/snapshot
   ID 274 gen 139 top level 259 path .snapshots/9/snapshot
   

   The output shows the top-level ID 5 and the existing snapshots. We’re interested in the root snapshot we created at the beginning of this tutorial.

2. Get the subvolid of the snapshot subvolume.

   SNAP_ID="$(sudo btrfs inspect-internal rootid /.snapshots/root)"
   echo $SNAP_ID
   

   Where /.snapshots/root is the snapshot before any changes. The $SNAP_ID should match the ID value shown when running sudo btrfs subvolume list /.

3. Set the default subvolume for the root file system.

   sudo btrfs subvolume set-default $SNAP_ID /
   

4. Confirm the change for the root file system’s default subvolume.

   sudo btrfs subvolume get-default /
   
   

   Example Output:

   ID 261 gen 60 top level 259 path root/.snapshots/root
   

5. Ensure that the GRUB command line does not overwrite your settings.

   current_grub_kernel=$(sudo grubby --default-kernel);
   sudo grubby --remove-args="rootflags=subvol=root" --update-kernel $current_grub_kernel
   

6. Reboot the system.

   sudo reboot
   

7. After the reboot, check that the root file system mounts the snapshot subvolume ID and subvolume.

   sudo mount|grep 'on / '
   

   Example Output:

   /dev/vda1 on / type btrfs (rw,relatime,seclabel,space_cache=v2,subvolid=261,subvol=/root/.snapshots/root)
   

8. Check for the existence of git.

   which git
   

   The output states that there is no git on the system. The git command is absent because the snapshot we are now running was created before we installed the Git package and its dependencies.

9. View the status of Snapper.

   sudo snapper ls
   

   The output shows you can still manage the existing snapshots.

Summary

That completes our introduction to using Btrfs as your root file system and the capabilities of using subvolumes, snapshots, and the Snapper utility. When you leverage these features, you can recover from most situations. If you want a utility that performs a full system recovery, check out our tutorial using ReaR.

For More Information

• Snapper
• Managing the Btrfs File System
• Oracle Linux Documentation
• Oracle Linux Training
• Oracle Linux Training Station

More Learning Resources

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