Trouble automounting a LUKS parition that is on a mdadm raid6
from Hercules@lemmy.world to selfhosted@lemmy.world on 21 Jun 15:30
https://lemmy.world/post/48456930

Hi fellow selfhoster,

Im a bit lost on the following scenario and im unable to find any documentation about it so i was hoping some smart people here could point me in the right direction.

I have a linux software raid 6 that contains a LUKS partition with ext4 in it. I would like to automount the ext4 when im rebooting. The root partition is also using LUKS and i have successfully setup the decryption for this parition but im uncertain on how to do this with this raid setup since im not sure where in the boot process linux recognizes my raid and when the decryption happens.

This is what i have:

[root@nfs-rocky-1 ~]# cat /etc/mdadm.conf
ARRAY /dev/md/server1:0 metadata=1.2 UUID=3e198408:2236ed3d:1dc13a8e:e5f91e52

On a reboot the raid does get automaticly recognizes but i still have to do cryptsetup luksOpen /dev/md0 raid & mount /dev/mapper/raid /mnt/data.

What would be the best way to do this? Im a bit scared of doing this im not certain of since i don’t want my machine to be stuck at a boot.

Just a like to an article that dicusses something like this already would help me greatly.

#selfhosted

threaded - newest

db_geek@norden.social on 21 Jun 16:01 next collapse

@Hercules I have a similar setup with RAID1 and BTRFS.
I'm using a keyfile for that:
dd bs=512 count=4 if=/dev/random of=/etc/crypttab.d/keyfile-data.bin iflag=fullblock
chmod 600 /etc/crypttab.d/keyfile-data.bin

cryptsetup luksAddKey /dev/mapper/raid /etc/crypttab.d/keyfile-data.bin --new-key-slot 1

entry in /etc/crypttab:
data UUID=<blkid from /dev/md0> /etc/crypttab.d/keyfile-data.bin luks

entry in /etc/fstab:
UUID=<blkid from /dev/mapper/raid> /mnt/data .....

Hercules@lemmy.world on 21 Jun 16:05 next collapse

Thanks for your response!

I will give it a try. Have a great rest of your day!

db_geek@norden.social on 21 Jun 16:06 next collapse

Another way can be pam_mount, which I'm using on an SBC for opening an encrypted device:
https://inai.de/projects/pam_mount/

Hercules@lemmy.world on 21 Jun 16:08 next collapse

Is the /etc/crypttab.d path that you are using specificly chosen or can it be whatever? This path doesn’t exists on my system and online i don’t see any mentions of it.

db_geek@norden.social on 21 Jun 16:11 next collapse

@Hercules I created it on my own, because I have some keys for other devices, too.
But you can place it, where you want.
But with crypttab.d I have a simple connection to crypttab configuration file.

nublug@piefed.blahaj.zone on 21 Jun 16:26 collapse

the crypttab.d thing is called a drop-in directory. linux will read files you make in these and overwrite the config files with the values in the drop-in files. it’s a way to add your own edits to config files without editing the default config files directly, so you don’t have to say manually copy crypttab to crypttab.old for a backup and instead always have a default config to fall back to if things go wrong by just commenting out your few changes in the drop-in file.

Hercules@lemmy.world on 21 Jun 16:24 collapse

:D while your steps were very clear i think i fked up.

cryptsetup luksAddKey /dev/mapper/raid /etc/crypttab.d/keyfile-data.bin --new-key-slot 1 gave: Device /dev/mapper/raid is not a valid LUKS device.. I assume this is a typo from your end since /dev/md0 is my luks volume. But altering this gave me: slot is already in use kind of error.

That can be explained since i tested something simular like you suggested earlier. Afterwhich i removed my key i generated and added to the volume. Then i did cryptsetup luksRemoveKey /dev/md0.

Now when i try to add it i get No key available with this passphrase.

I don’t have enough knowledge about cryptsetup to know what excactly i did wrong.

Do you by any change have an explaination?

In case this is usefull:

[root@nfs-rocky-1 ~]# cryptsetup luksDump /dev/md0
LUKS header information
Version:       	2
Epoch:         	6
Metadata area: 	16384 [bytes]
Keyslots area: 	16744448 [bytes]
UUID:          	485df758-6cec-49e3-aceb-438aaaedc833
Label:         	(no label)
Subsystem:     	(no subsystem)
Flags:       	(no flags)

Data segments:
  0: crypt
	offset: 16777216 [bytes]
	length: (whole device)
	cipher: aes-xts-plain64
	sector: 4096 [bytes]

Keyslots:
  1: luks2
	Key:        512 bits
	Priority:   normal
	Cipher:     aes-xts-plain64
	Cipher key: 512 bits
	PBKDF:      argon2id
	Time cost:  4
	Memory:     1048576
	Threads:    4
	Salt:       17 c5 ff 7f b9 10 43 41 16 5a c8 28 44 b9 df 64
	            a8 1d 40 41 9f a1 70 85 34 06 52 8d ba 29 bd ef
	AF stripes: 4000
	AF hash:    sha256
	Area offset:290816 [bytes]
	Area length:258048 [bytes]
	Digest ID:  0
  2: luks2
	Key:        512 bits
	Priority:   normal
	Cipher:     aes-xts-plain64
	Cipher key: 512 bits
	PBKDF:      argon2id
	Time cost:  12
	Memory:     1048576
	Threads:    4
	Salt:       64 97 db 49 f1 18 b9 57 3b 02 53 37 b3 11 8e 44
	            71 d1 70 b2 b9 58 4c db e2 6b 36 95 7c dd d2 be
	AF stripes: 4000
	AF hash:    sha256
	Area offset:548864 [bytes]
	Area length:258048 [bytes]
	Digest ID:  0
Tokens:
Digests:
  0: pbkdf2
	Hash:       sha256
	Iterations: 105703
	Salt:       ae ac f1 9f df 47 27 9e 64 28 52 53 9a 9b cd 77
	            74 15 66 f6 8b 3c bd f4 29 dc f1 b1 c5 15 3b f6
	Digest:     07 5f 2f 6b d3 c5 bf b6 54 58 5e b4 44 df 8c b8
	            2b da fa 5c 40 a5 89 cc 0e 3b 70 69 57 d5 7c f5
[root@nfs-rocky-1 ~]#
db_geek@norden.social on 21 Jun 17:10 collapse

@Hercules My exampled assumed, that you only have a password set on keyslot 0.

LUKS keyslots are starting at 0, so it seems, that you deleted the initial set password.
I hope, you know the other keyslots.

As far I can see, you can specify, which keyslot has to be selected for unlocking the volume key.
More information you can find in the man page.
```
man cryptsetup-luksaddkey

cryptsetup luksAddKey /dev/md0 --new-key-slot 0 --key-slot 1
```

Hercules@lemmy.world on 21 Jun 17:52 collapse

Just to give you an update. The other keyslot was the key i added earlier for testing which i removed … So its time for me to copy over a lot of data to another system en recreate the luks volume. Thanks for your help!

nublug@piefed.blahaj.zone on 21 Jun 16:13 collapse

i don’t know anything about raid, but judging by your manual command to unlock and mount it shouldn’t be any different than my non-raid extra encrypted disks setup.

it should be just adding it to crypttab and fstab and a keyfile and grub config edit maybe, and if you mess up you can still get in to edit these to try again with a liveusb (easiest way to go back to previous setup is just comment out the lines you add) and manually unlocking and mounting like you are now anyway, so don’t be scared.

https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_entire_system

is a lot but the specific info you need for your setup should be various places there and linked there. good luck!