Chroot into a btrfs uefi system from live media

General system
1

Can somebody point me to the instructions for this. I don’t have a problem, but will have at some point!!!

2

The only real difference between a btrfs chroot and an ext4 chroot is that you need to add -o subvol=@ to your mount line. That assumes that your root subvolume is name @. If it is named something else, use that instead.

For most people, that is all you have to do.

If you have carved your system up into many subvols, you will need to mount those as well if they are relevant. For example, if you have /home in a separate subvol, you probably don’t need that in a chroot. But if you put /usr or /var in a separate subvol, you need to mount those too.

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3 
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   1.8T  0 disk
└─sda1   8:1    0   1.8T  0 part /data
sdb      8:16   0 232.9G  0 disk
├─sdb1   8:17   0   300M  0 part /boot/efi
├─sdb2   8:18   0 223.8G  0 part /home
│                                /
└─sdb3   8:19   0   8.8G  0 part [SWAP]
sdc      8:32   1  57.3G  0 disk
├─sdc1   8:33   1  57.2G  0 part /run/media/xircon/ventoy
└─sdc2   8:34   1    32M  0 part

So:

sudo mount /dev/sdb1 /mnt #efi
sudo mount /dev/sdb2  /mnt/root -o subvol=@
sudo arch-chroot /mnt

Sorry, really really warm today and we brits do not function well unless it is cold and wet :rofl:

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4

I think more like this:

sudo mount /dev/sdb2 /mnt -o subvol=@
sudo mount /dev/sdb1 /mnt/boot/efi
sudo arch-chroot /mnt
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5

Either drink a cold beer, or pour the cold beer on yourself? :crazy_face:
Both of them should help… :wink:

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6

Thanks @dalto that works - now lets hope I never need it :smiley:

7

29 deg C outside, 26 inside, wish I could drink beer, but alcohol + prescription medication = really bad hangover :frowning:

I prefer cold, cold you can put on clothes, if I take off anymore I will be arrested for public indecency :rofl:

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8

Today is about the first day here (in southern Finland) the temperature is below 30 degrees C outside during this Summer… And inside I now have 28!

So under the shower is the only place for survival… :rofl:

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9

I am using Btrfs on LUKS . So should I use the luks device instead , like

sudo mount /dev/mapper/luks-UUID /mnt -o subvol=@
sudo mount /dev/sda1 /mnt/boot/efi
sudo arch-chroot /mnt

??

11

Your luks-device should have a ‘mapped’ name, e. g. ‘crypt’. Use that.

For example:

sudo cryptsetup luksOpen /dev/sda2 crypt &&
sudo mount -o compress=zstd,subvol=@ /dev/mapper/crypt /mnt

Then. chroot into your system
sudo arch-chroot /mnt

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12

Yes, exactly. For a manual mount it doesn’t really matter how you refer to the luks device. You can use any of the valid device names. Use whichever one you find easiest. I usually the one in /dev/disk/by-id but it doesn’t matter much.

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