Configuring BTRFS on Arch

This guide is for anyone who's just installed Arch Linux with GRUB and BTRFS. I'm going to keep things straightforward, using the defaults set up by archinstall. If you're ready, let's dive in!

Install Required Packages

First things first, we need some essential tools to manage BTRFS effectively. Open up your terminal and run:

sudo pacman -S snapper snap-pac grub-btrfs

What Are These Packages?

Snapper: This handy tool helps you create and manage BTRFS snapshots. Think of snapshots as save points in a video game—they let you revert your system to a previous state if something goes wrong.
Snap-pac: This adds a hook to pacman, Arch's package manager. Basically, it automatically takes a snapshot before or after you install, remove, or upgrade packages. This is super useful because if an update breaks something, you can roll back without a hassle.
Grub-btrfs: This package helps integrate BTRFS with your bootloader, GRUB. It makes it easier to manage boot entries and snapshots from the boot menu.

Procedure

Clean Up Existing Snapshots

If this is a fresh install, you likely don't have any snapshots yet, but just to be sure, let's remove any existing ones:

sudo umount /.snapshots
sudo rm -r /.snapshots

Create a New Root Config

Now, let's create a configuration for the root filesystem. This will set up a place for your snapshots to live:

sudo snapper -c root create-config /

This command creates a subvolume /.snapshots where all your snapshots will be stored. It's like giving your snapshots a nice home!

Reinitialize Snapshots

Next, we need to make sure the .snapshots directory is accessible:

sudo mkdir /.snapshots
sudo mount -a

This mounts the .snapshots subvolume so Snapper can actually use it.

Fix Some Permissions

Let's set the right permissions to ensure everything works smoothly:

sudo chmod 750 /.snapshots
sudo chown :wheel /.snapshots

These commands set the permissions so that only the root and users in the wheel group can access the snapshots, keeping your system secure.

Enable Automatic Snapshotting

To make your life easier, we want to enable automatic snapshotting. This way, you won't have to remember to take snapshots manually:

sudo systemctl enable --now snapper-timeline.timer snapper-cleanup.timer

This enables two timers: one for creating snapshots automatically at set intervals, and another for cleaning up old snapshots to save space.

Add Snapshots to GRUB

To make sure you can boot into your snapshots, you need to configure GRUB. Open the GRUB configuration file and ensure this line is present:

GRUB_BTRFS_GRUB_DIRNAME="/boot/efi"

This tells grub-btrfs where to find the GRUB directory.

Enable grub-btrfsd

Next, we want to set up grub-btrfsd to automatically generate the grub-btrfs.cfg file whenever you make changes. You can enable it with:

sudo systemctl enable --now grub-btrfsd

This service will keep your GRUB menu up to date with the latest snapshots, so you can easily boot into a previous state if needed.

Chrooting into a BTRFS System

If you ever need to troubleshoot or repair your system, you might need to chroot into your BTRFS environment. Here's how:

Boot from an Arch Linux live USB.
Open a terminal.

First, you need to mount your BTRFS subvolumes correctly. Here's how you can do that with the default setup from archinstall:

mount -o subvol=@ /dev/sdXY /mnt
mount -o subvol=@home /dev/sdXY /mnt/home
mount -o subvol=@pkg /dev/sdXY /mnt/var/cache/pacman/pkg
mount -o subvol=@log /dev/sdXY /mnt/var/log
mount -o subvol=@snapshots /dev/sdXY /mnt/.snapshots
mount /dev/sdXZ /mnt/boot

Replace /dev/sdXY and /dev/sdXZ with your actual device identifiers (you can find these using lsblk).

Once everything is mounted, enter the chroot environment:
```
arch-chroot /mnt
```

You're now inside your system's environment and can make changes as needed.

System Rollback the Arch Way

One of the coolest features of BTRFS is its snapshot capability, which allows you to roll back your system if something goes wrong. Here's how to do it, based on points from the Arch Wiki:

List Existing Snapshots: First, check your existing snapshots to see what you have:
```
sudo snapper list
```
This will show you a list of snapshots, along with their IDs.
Roll Back to a Previous Snapshot: If you find a snapshot that you want to revert to, you can use the following command:
```
sudo snapper rollback <snapshot_id>
```
Replace <snapshot_id> with the ID of the snapshot you want to roll back to.
Reboot Your System: After rolling back, reboot your system to apply the changes:
```
sudo reboot
```

When your system starts back up, it will be in the state it was at the time of that snapshot.

Important Note

Rolling back will restore the files in the root subvolume to their state at the time of the snapshot. However, be careful—any changes made after the snapshot will be lost. Always ensure you have backups of important data before rolling back.

Conclusion

And there you have it! You've successfully configured BTRFS on your Arch Linux installation, set up automatic snapshots, and learned how to roll back your system when needed. This setup not only enhances your system's stability but also gives you peace of mind, knowing you can revert to a previous state if something breaks.

Feel free to play around with the snapshots and see how they work—it's a powerful feature that can save you a lot of headaches in the long run. Happy tinkering!