Re: Btrfs default subvolume, /home

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On Sat, 2011-11-05 at 22:22 -0400, Eric Griffith wrote:
> Hey guys, I've been trying out BTRFS the last couple days, just to
> kind of see what to expect and what I can do with it once its
> finalized and we have a working fsck. I do have a couple question that
> neither the Arch Wiki, The Fedora WIki, Ubuntu wiki or the kernel.org
> wiki could answer. So here goes;
> 
> 
> When I installed fedora (F16 Beta) I made root be an ext4 partition,
> with /home as BTRFS. Ubuntu wiki states that any BTRFS partition has a
> default subvolume called "default," I cant find it for /home.
> 
> /etc/fstab:
> 
> #
> # /etc/fstab
> # Created by anaconda on Thu Nov 3 15:24:14 2011
> #
> # Accessible filesystems, by reference, are maintained under '/dev/disk'
> # See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
> #
> UUID=e5021a48-c961-4e73-98a5-beee06355f46 / ext4 defaults 1 1
> UUID=97ac420f-2818-4833-b7b6-4ac497716e3b /home btrfs
> defaults,autodefrag,compress 1 2
> UUID=0d275462-1ad3-46af-a1b8-637ca5efeca6 swap swap defaults 0 0
> 
> 
> btrfs --help says. "btrfs subvolume list <path> : List the
> snapshot/subvolume of a filesystem." I'd expect it to spit out
> "default" at some point.
> 
> Couple outputs
> 
> [eric@eric-laptop ~]$ sudo btrfs subvolume list /
> ERROR: '/' is not a subvolume
> [eric@eric-laptop ~]$ sudo btrfs subvolume list /home
> [eric@eric-laptop ~]$
> 

It doesn't list the root volume (0). I'm not sure if it ever did - it is
root volume so it might not "sub"volume.

> What i wanted was an easy; reliable way to keep a backup of my home
> using btrfs instead of just rsync. Unfortunately, in order to use
> snapshot, it needs to be on, or be a, subvolume.
> 

Remember that snapshots are not backups. If anything damages your
partition, or even sector your file is in, you have troubles.

> proof:
> 
> [eric@eric-laptop ~]$ sudo btrfs subvolume snapshot /home/eric /home/eric/test
> ERROR: '/home/eric' is not a subvolume
> [eric@eric-laptop ~]$
> 

Why not (with eric back on /home):

btrfs subvolume snapshot /home /home/snapshot-$(date -u +"%Y%m%d")

Snapshots are not recursive.

(It works for me with integration-20111030 but not integration-20111012
on 3.1.0+)

> 
> So; I rebooted into single user, mv'ed /home/eric to /home/eric-btrfs,
> made a subvolume in /home/ named 'eric' to take the place of my home,
> and cp'ed all of my files from eric-btrfs to eric, a quick chown, and
> chmod to get the file permissions right.
> 
> Rebooted, tried to login... error messages, lots of error messages.
> "Cant switch out from /" "/home/eric/.kde/share/config/knotifyrc is
> not writable" despite having read and write permission, and ownership.
> 

Can you log in from tty to check whether you can access $HOME? I'm not
btrfs developer but I am not sure if you can have subvolume owned by
non-root.

> Can anyone figure out what the heck is going on? I know BTRFS is still
> experimental, but I thought the layout and implementation was
> finalized. OR; what do I have to do to make Btrfs work as a /home as
> it should? (see ZFS / LVM )

Regards

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