Arch Linux

syntonym

Member

Registered: 2015-06-24

Posts: 3

[SOLVED] BTRFS filesystem is changed to ro if user tries to login

I have two different users I use to login into my system, one "main" and one "guest" user. If the guest user logs in (before anything interestinig happens, on the standard terminal before using startx) systemd-journald complains that it cannot write, mount shows that / and /home are suddenly mounted as ro. This does not happen if I login with my main user.

I've the following partioning scheme:
sda1: btrfs bootpartition (later mounted on /boot)
sda2: crypto_LUKS
sda3: btrfs (not used)

the encrypted sda2 is a btrfs filesystem with two subvolumes, root and home. root is mounted on / and home on /home .

This is my syslinux entry I use to boot:

LABEL arch
    MENU LABEL Arch Linux
    LINUX ../vmlinuz-linux
    APPEND cryptdevice=/dev/sda2:cryptroot root=/dev/disk/by-label/main rw
    INITRD ../initramfs-linux.img

This is my fstab:

# /dev/mapper/cryptroot LABEL=main
UUID=03433ebf-091b-40ee-81c7-39af59b425cf	/         	btrfs     	rw,relatime,ssd,space_cache	0 0

# /dev/mapper/cryptroot LABEL=main
UUID=03433ebf-091b-40ee-81c7-39af59b425cf	/home     	btrfs     	rw,relatime,ssd,space_cache,subvol=home	0 0

# /dev/sda1 LABEL=boot
UUID=0f61e371-68f9-473e-8856-a01babaeffc3	/boot     	btrfs     	rw,relatime,ssd,space_cache	0 0

The guest user is in two groups my main user is not part of: floppy and power (probably because I used the adduser script and forgot to remove these two groups..)

How can this happen? Only root does have the permission to mount things, so how can a regular user mess things up? I guess I have some faulty config somewhere? I've got no clue how I should start to debug this, so any hint is appreciated.

Last edited by syntonym (2015-06-24 18:00:49)

WorMzy

Forum Moderator

From: Scotland

Registered: 2010-06-16

Posts: 11,896

Website

Re: [SOLVED] BTRFS filesystem is changed to ro if user tries to login

Hi syntonym, welcome to the Arch Linux forums.

A good place to start debugging this would be looking at the journal. What messages are recorded aroudn the time of the user logging in? Specifically, are there any kernel messages?

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syntonym

Member

Registered: 2015-06-24

Posts: 3

Re: [SOLVED] BTRFS filesystem is changed to ro if user tries to login

I feel like a complete moron not to think of inspecting the journal. Turns out the btrfs has hicked up and a mount with recovery bootflag fixed the problem. In the journal that showed up as

parent transid verify failed on 109973766144 wanted 1823 found 1821

More information for anyone encountering a similiar situation can find additional information in this blogpost.

Thanks WorMzy!

Last edited by syntonym (2015-06-24 18:16:33)