Re: rollback of a snapshot is just read-only

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-04-24 10:26, Lentes, Bernd wrote:
> Hi,
>
> it should be just a small problem, but it is one. How can I rollback to a snapshot of my root filesystem ?
> Googeling, I found a lot of solutions, each different.
> I finally choosed this one: https://btrfs.wiki.kernel.org/index.php/UseCases#I_want_to_be_able_to_do_rollbacks_with_Btrfs
>
> I made the snapshot, changed some configuration, and afterwards I'd like to rollback to the snapshot:
>
> - btrfs subvolume snapshot -r  /  /.snapshots/vor_nvidia
>
> - change some configuration
>
> - btrfs subvolume set-default 625 (id of the snapshot)
>
> - reboot
>
> My /-folder is again the old one, that's ok. The change of the configuration has disappeared. But it is just read-only:
> pc63422:~ # touch /test
> touch: cannot touch '/test': Read-only file system
>
> mount says:
>
> ...
> /dev/sda1 on /  type btrfs (rw,ssd,space_cache)
> ...
>
> It seems to be rw !?
>
> OS: SLES 12 64bit
> kernel: 3.12.38-44-default
>
> pc63422:~ # rpm -qa|grep -i btrfs
> btrfsprogs-3.16.2-7.1.x86_64
> libbtrfs0-3.16.2-7.1.x86_64
> btrfsmaintenance-0.1-7.1.noarch
>
> pc63422:~ # btrfs --version
> Btrfs v3.16.2+20150127
>
> pc63422:~ # btrfs fi show
> Label: none  uuid: 7edcb64a-4ca6-47ec-8979-54e158c96ac2
>          Total devices 1 FS bytes used 145.19GiB
>          devid    1 size 450.00GiB used 150.04GiB path /dev/sda1
>
> pc63422:~ # btrfs fi df /
> Data, single: total=146.01GiB, used=142.74GiB
> System, single: total=32.00MiB, used=16.00KiB
> Metadata, single: total=4.00GiB, used=2.44GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
>
> Thanks for any hint.
>
>
So, a snapshot being read-only is totally different from the FS being 
mounted read-only.  There is a special property on the snapshot that 
determines whether it is read-only or writable, which is first set when 
the snapshot is created.  To change that property so that the snapshot 
is writable, you can use the following command from the top directory of 
the snapshot:
     btrfs property set . ro false



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