how to replay a snapshot (btrfs) ?
bernd.lentes at helmholtz-muenchen.de
Tue Jul 26 15:40:17 UTC 2016
----- On Jul 26, 2016, at 2:55 PM, Bernd Lentes bernd.lentes at helmholtz-muenchen.de wrote:
> sorry for asking this simple question. But i'm new to btrfs. And all the guides
> i found in the internet are different and none of them succeeded.
> I made a snapshot form my / , did some changes in the configurtaion (which
> weren't successfull), now i want to get back to the snapshot.
> This is my system:
> root at PC65472:~# btrfs sub list -ap /
> ID 257 gen 38915 parent 5 top level 5 path <FS_TREE>/@
> ID 258 gen 38903 parent 5 top level 5 path <FS_TREE>/@home
> ID 285 gen 38828 parent 257 top level 257 path @/snapshots/root_190720162124
> ID 285 is my snapshot.
> root at PC65472:~# btrfs sub get-default /
> ID 285 gen 38828 top level 257 path snapshots/root_190720162124
> I changed the snapshot to the default but i still have the configuration changes
> i'd like to loose.
> Also after a restart still no replay of the snapshot.
> root at PC65472:~# mount|grep -iE 'btrfs|subvol'
> /dev/mapper/vg1-lv_root on / type btrfs
> /dev/mapper/vg1-lv_root on /home type btrfs
> /dev/mapper/vg1-lv_root on /mnt/snap type btrfs
> I can mount my snapshot, which is fine and logical, but where is the benefit ?
> How can i set the snapshot to be my new live-system ?
> System is Ubuntu 16.04 64 bit kernel 4.4.0-31.
> In the btrfs wiki i read:
> mount -o subvolid=0 <filesystem> <mount-point>
> But that does not succeed:
> root at PC65472:~# mount -o subvolid=0 /dev/mapper/vg1-lv_root /
> mount: /dev/mapper/vg1-lv_root is already mounted or / busy
> /dev/mapper/vg1-lv_root is already mounted on /
> /dev/mapper/vg1-lv_root is already mounted on /home
> /dev/mapper/vg1-lv_root is already mounted on /mnt/snap
> And umounting / of course also does not succeed.
> Thanks for any help.
here (https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Snapshots) i found that:
"Once a [writable] snapshot is made, there is no difference in status between the original subvolume, and the new snapshot subvolume.
To roll back to a snapshot, unmount the modified original subvolume, use mv to rename the old subvolume to a temporary location,
and then again to rename the snapshot to the original name. You can then remount the subvolume."
I can't unmount / in a running system. I had to do that with s.th. like Knoppix, but that's inconvenient.
Isn't there a way without a live cd, using the running system ?
What is about modifying my fstab?
Here it is:
# <file system> <mount point> <type> <options> <dump> <pass>
/dev/mapper/vg1-lv_root / btrfs defaults,subvol=@ 0 1
# /boot was on /dev/sda1 during installation
UUID=290aabb0-cd7a-4094-bdb4-9b7ed3538f2b /boot ext3 defaults 0 2
/dev/mapper/vg1-lv_root /home btrfs defaults,subvol=@home 0 2
# swap was on /dev/sda3 during installation
UUID=62189b48-ac0b-480e-a06a-7e602e27882c none swap sw 0 0
Can't i change the first line to
"/dev/mapper/vg1-lv_root / btrfs defaults,subvol=snapshots/root_190720162124 0 1" ?
Can i delete the snapshot afterwards ?
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