Hi,

i'm still pretty new in BTRFS. I created a snapshot because i made changes in the system. Now system is a bit messed up and i want to roll back to the snapshot.

That's what i did:

create a read-only snapshot from my root:
btrfs sub snapshot -r / pre_kde

which creates the following snapshot:
/.snapshots/pre_kde

fiddle around

want to roll back

I followed a procedure which succeede under Ubuntu:

mount the default subvolume:
mount /dev/sda2 /mnt/sda2/ -o subvolid=5

cd to there:
cd /mnt/sda2

ls show one directory:
@

create a snapshot from the snapshot:
btrfs sub snap /.snapshots/pre_kde/ @
creates a snapshot @/pre_kde which i didn't want

rename:
mv -v @ @_alt

create a snapshot from the snapshot (it's twice, i know :-))
btrfs sub snap @_alt/pre_kde/ @
Now i have a snapshot called @ which is what i wanted

All previous snapshots are now under @_alt, and the desired snapshot is under @.

Reboot

System didn't boot.

As i said, with Ubuntu i succeeded.

What is wrong ?

Btw: I have the following snapshot (retrieved from the same system, booted with Knoppix):
btrfs sub show @_alt/.snapshots/1/snapshot
/mnt/sda2/@_alt/.snapshots/1/snapshot
Name: snapshot
UUID: 23b8eb3c-13aa-9a4c-af7e-ca04639d968c
Parent UUID: 1baca319-0888-5f49-b87b-bfefb598c77f
Received UUID: -
Creation time: 2016-09-19 17:54:09 +0200
Subvolume ID: 259
Generation: 21834
Gen at creation: 11
Parent ID: 258
Top level ID: 258
Flags: -
Snapshot(s):
@_alt/.snapshots/2/snapshot
@_alt/.snapshots/38/snapshot
@_alt/.snapshots/39/snapshot
@_alt/.snapshots/40/snapshot
@_alt/.snapshots/41/snapshot
@_alt/.snapshots/42/snapshot
@_alt/.snapshots/43/snapshot
@_alt/.snapshots/pre_kde
@_alt/.snapshots/44/snapshot
@_alt/.snapshots/45/snapshot
@_alt/.snapshots/46/snapshot
@_alt/.snapshots/47/snapshot

The snapshot is created on the 19th of september. Yes ?

Inside i have this file:

root@Microknoppix:/mnt/sda2/@_alt/.snapshots/1/snapshot/root# stat .bash_history
Datei: „.bash_history“
Größe: 29585 Blöcke: 64 EA Block: 4096 reguläre Datei
Gerät: 2ah/42d Inode: 159206 Verknüpfungen: 1
Zugriff: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)
Zugriff : 2016-09-28 09:36:25.001271739 +0200
Modifiziert: 2016-09-27 19:26:02.323945822 +0200
Geändert : 2016-09-27 19:26:02.323945822 +0200

How can i have inside a snapshot created on 19th of september a file which is modified on 27th of september ?

I thought a snapshot is a freezen image of the particular moment it is created.

Bernd