Post updated with simpler rollbacks

`snapper` and how to deal with problems

`snapper undochanges` for small problems

Let’s suppose you’ve updated a package, and the new version does not work anymore. apt should have triggered a snapshot, and thoses changes can be reverted.

I don’t have a situation like this on my system, but let’s pretend I have one, by installing a software, for instance ncdu. It’s a bad example, since ncdu is really usefull, but let’s do it:

Create a ~fake~ problem
```
sudo apt-get install -y ncdu
```

Identify the snapshots

snapper list
...
single | 255 |       | Tue 15 May 2018 07:00:09 PM CEST | root | timeline | timeline    |         
pre    | 256 |       | Thu 17 May 2018 08:24:12 PM CEST | root | number   | apt         |         
post   | 257 | 256   | Thu 17 May 2018 08:24:19 PM CEST | root | number   | apt         |     

apt has created a pre/post snapshots with numbers 257 and 256

Revert the changes

sudo snapper undochange 256..257
create:0 modify:6 delete:96

ncdu is not installed anymore, success!

⚠ `snapper rollback` for bigger problems ⚠

snapper rollback is not supported on ubuntu, mainly because SUSE Linux (the main contributor of snapper) uses a different filesystem layout.

However, since we’ve got snapshots, we can still recover manually from catastrophic failures.

Make sure you’ve got a bootable media for your machine.
Make sure you’ve got a recent backup.
NO, liten to me NOW!, make really really sure you’ve got a working backup and and a working bootable media for your machine, always.

Make sure you’ve got a good snapshot of your system, and /bin is on the snapshot

sudo touch /bin/test_today
snapper create -c timeline -d "about to destroy the system"
snapper list
...
single | 260 |       | Thu 17 May 2018 09:00:12 PM CEST | root | timeline | timeline                    |
single | 261 |       | Thu 17 May 2018 10:00:31 PM CEST | root | timeline | timeline                    |
single | 262 |       | Thu 17 May 2018 10:50:42 PM CEST | pim  | timeline | about to destroy the system |
...
snapper status 261..262
...
+..... /bin/test_today
...

Now I’m sure /bin is in my snapshots, let’s create a ~~fake~~ problem:
Create a ~~fake~~ problem.
```
sudo rm /bin/bash
```
Now reboot, (you won’t be able to login since bash is your default shell)
Reboot on your bootable media, select Rescue a broken system
Do as you do when you installed the system
Assemble the RAID array (automatic will do), then select your root device, mine is /dev/root/root
Execute a shell in the installer environment
Umount /target it is mounted with a wrong subvolume argument, and remount it
```
umount /target
mount /dev/root/root /target
```

Make a snapshot of the broken system

btrfs create subvolume snapshot -r /target/@ /target/@/.snapshots/broken

Restore

btrfs mv /target/@ /target/@_broken
btrfs subvolume snapshot /target/@_broken/.snapshots/261/snapshot /target/@
mv /target/@_broken/.snapshots /target/@
umount /target
sync

reboot (should work), then let’s have a look at snapper

snapper create -c timeline -d "system restored"
snapper list
...
single | 260 |       | Thu 17 May 2018 09:00:12 PM CEST | root | timeline | timeline                    |
single | 261 |       | Thu 17 May 2018 10:00:31 PM CEST | root | timeline | timeline                    |
single | 262 |       | Thu 17 May 2018 10:50:42 PM CEST | pim  | timeline | about to destroy the system |
single | 263 |       | Thu 17 May 2018 11:05:33 PM CEST | pim  | timeline | system restored             |

~~~

Question, remark, bug? Don't hesitate to contact me or report a bug.

snapper and how to deal with problems

snapper undochanges for small problems

⚠ snapper rollback for bigger problems ⚠

`snapper` and how to deal with problems

`snapper undochanges` for small problems

⚠ `snapper rollback` for bigger problems ⚠