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[solved] BtrFS root - booting read only  

post #1 of 45
Thread Starter 
I used the btrfs-convert tool on my ext4 volume and while the conversion was a success, now ArchLinux mounts root as read only. (I know the file system is fine as I can remount the file system once the OS has started)

I'm using syslinux, but I'm pretty sure it's not the boot menu that's the issue. I think it's a Linux config file I've missed somewhere; likely a really obvious and dumb mistake that I've over looked.

I believe the fstab is correct (and I have changed a few settings in there just in case). And I've added btrfs to mkinitcpio.

Anyone else have any suggestions?
post #2 of 45
can you mount rw after boot?

# mount -o remount,rw /;
post #3 of 45
Post fstab (cat /etc/fstab) and post the last 100 lines of dmesg (dmesg | tail -n 100) after boot.
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post #4 of 45
You used a file system conversion tool; you are braver than me biggrin.gif
post #5 of 45
Thread Starter 
Quote:
Originally Posted by particleman72 View Post

can you mount rw after boot?

# mount -o remount,rw /;
I did already say I could tongue.gif
Quote:
Originally Posted by gonX View Post

Post fstab (cat /etc/fstab) and post the last 100 lines of dmesg (dmesg | tail -n 100) after boot.
The last 100 lines wouldn't be of much use as that's all just wifi and other such crap. There is this further up though:
Code:
$ dmesg | egrep -i "(btrfs|sda)"                                                                                                                
[    0.000000] Command line: root=/dev/sda1 ro initrd=../initramfs-linux.img BOOT_IMAGE=../vmlinuz-linux                                                                
[    0.000000] Kernel command line: root=/dev/sda1 ro initrd=../initramfs-linux.img BOOT_IMAGE=../vmlinuz-linux 
[    1.412671] sd 0:0:0:0: [sda] 125045424 512-byte logical blocks: (64.0 GB/59.6 GiB)
[    1.412745] sd 0:0:0:0: [sda] Write Protect is off
[    1.412749] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
[    1.412782] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[    1.414982]  sda: sda1
[    1.415445] sd 0:0:0:0: [sda] Attached SCSI disk
[    1.487440] Btrfs loaded
[    1.488171] device fsid b9a11d9a-7db6-46c3-b2f4-9b651f3e108b devid 1 transid 395 /dev/sda1
[    1.806315] device fsid b9a11d9a-7db6-46c3-b2f4-9b651f3e108b devid 1 transid 395 /dev/sda1
[    2.245862] device fsid b9a11d9a-7db6-46c3-b2f4-9b651f3e108b devid 1 transid 395 /dev/sda1
[    2.460893] device fsid b9a11d9a-7db6-46c3-b2f4-9b651f3e108b devid 1 transid 395 /dev/sda1
[    2.461807] btrfs: disk space caching is enabled
[    2.463332] btrfs: mismatching generation and generation_v2 found in root item. This root was probably mounted with an older kernel. Resetting all new fields.
[    2.463794] btrfs: mismatching generation and generation_v2 found in root item. This root was probably mounted with an older kernel. Resetting all new fields.
[    2.480639] Btrfs detected SSD devices, enabling SSD mode
[    2.481025] btrfs: mismatching generation and generation_v2 found in root item. This root was probably mounted with an older kernel. Resetting all new fields.
[    5.786825] device fsid b9a11d9a-7db6-46c3-b2f4-9b651f3e108b devid 1 transid 397 /dev/sda1
[    5.787612] btrfs: disk space caching is enabled
[    5.809776] Btrfs detected SSD devices, enabling SSD mode
[    5.809797] btrfs: mismatching generation and generation_v2 found in root item. This root was probably mounted with an older kernel. Resetting all new fields.
[    6.465721] device fsid b9a11d9a-7db6-46c3-b2f4-9b651f3e108b devid 1 transid 397 /dev/sda1
[   25.171509] btrfs: disk space caching is enabled
Code:
#UUID=58a3c64f-ba75-4f44-bad2-a24b05331b6a      /               btrfs           defaults,compress,ssd,discard           0 0
UUID=/dev/sda1               /               btrfs           defaults,noatime,discard,ssd,compress   0 0
I've just noticed that I've garbled up the fstab (used a block device against UUID), so going to fix that and reboot

[edit]
yeah that fixed it. Dumb mistake. I can't believe I missed that yesterday. Still, I did suspect it was something stupid I'd overlooked.

Thanks for your help
Quote:
Originally Posted by CaptainBlame View Post

You used a file system conversion tool; you are braver than me biggrin.gif
I know what you mean. I'm hoping to convert my work desktop to Btrfs to take advantage of snapshotting, however I thought I'd better check the conversion tool at home (where it matters less) first. Plus I wanted to get the feel of just how mature Btrfs is before committing to it.

Honestly though, even just with these little tests (and I'm not in any way blaming the booting in read only on Btrfs), I'm largely unimpressed. It's pretty obvious from using it that it's designed to be a copy of ZFS, yet the CLI tools aren't near as clean and user friendly. I honestly do wish Oracle (or whoever's decision it was) just wrote new ZFS drivers for Linux instead of trying to reinvent a crappier version of ZFS.
Edited by Plan9 - 3/23/13 at 2:48am
post #6 of 45
Good to hear you fixed it. You don't need to use the 'defaults' option in the fstab if you are specifying something else.
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post #7 of 45
Thread Starter 
Quote:
Originally Posted by gonX View Post

Good to hear you fixed it. You don't need to use the 'defaults' option in the fstab if you are specifying something else.

This is what I thought too, but every single article I found, when googling the problem, did put defaults + other options:
https://btrfs.wiki.kernel.org/index.php/SysadminGuide
https://wiki.archlinux.org/index.php/Installing_on_Btrfs_root#.2Fetc.2Ffstab
http://tincman.wordpress.com/2011/01/20/installing-arch-linux-onto-a-gpt-partitioned-btrfs-root-ssd-on-a-legacy-bios-system/
post #8 of 45
Thread Starter 
Btrfs is an abomination.

Every single thing that ZFS got right, btrfs completely cocked up. There isn't even a simple was to roll back snapshots. Its just the worst.
post #9 of 45
Quote:
Originally Posted by Plan9 View Post

Btrfs is an abomination.

Every single thing that ZFS got right, btrfs completely cocked up. There isn't even a simple was to roll back snapshots. Its just the worst.

Wait so snapshots don't work or what? I'm totally confused on Btrfs as when I first used it back in 2010 with MeeGo it was faster than it is now...it also seemed to have less features working. So what's the point in going to btrfs (IIRC isn't it supposed to be the ext4 replacement in the future?) because I'm trying it on one Linux install and it has atrocious slow boots now and shutdowns.
     
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post #10 of 45
Thread Starter 
Quote:
Originally Posted by Rookie1337 View Post

Wait so snapshots don't work or what? I'm totally confused on Btrfs as when I first used it back in 2010 with MeeGo it was faster than it is now...it also seemed to have less features working. So what's the point in going to btrfs (IIRC isn't it supposed to be the ext4 replacement in the future?) because I'm trying it on one Linux install and it has atrocious slow boots now and shutdowns.

It's snapshots fine. It doesn't have any in built rollback feature (or at least none that I can fine) so you're basically expected to rsync your data manually (as one guide suggests)
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