how to rollback / to a snapshot ?

* how to rollback / to a snapshot ?
@ 2021-05-26 13:05 Lentes, Bernd
  2021-05-26 14:08 ` Remi Gauvin
  0 siblings, 1 reply; 13+ messages in thread
From: Lentes, Bernd @ 2021-05-26 13:05 UTC (permalink / raw)
  To: Btrfs ML

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Hi,

sorry for asking such a simple question, but ...
i didn't find that in the BTRFS wiki and googleing i found tons of ways, but all different, so now i'm more confused than before.
And it's the first time i have to do that.
I have an Ubuntu box where an upgrade didn't complete. System was 16.04 before, now it "thinks" it's an 18.04, but it still uses the kernel from 16.04 ! 
System is up and running. I don't like to use a live linux for the rollback because i'm currently in quarantine and i can't get physically to the box, just with ssh.

This is my setup:

root@pc65472:/boot# mount |grep btrfs
/dev/mapper/vg1-lv_root on / type btrfs (rw,relatime,ssd,space_cache,subvolid=257,subvol=/@)
/dev/mapper/vg1-lv_root on /home type btrfs (rw,relatime,ssd,space_cache,subvolid=258,subvol=/@home)
/dev/sdb1 on /data type btrfs (rw,relatime,space_cache,subvolid=258,subvol=/@data)
/dev/sdc1 on /local type btrfs (rw,relatime,space_cache,subvolid=5,subvol=/)
/dev/mapper/vg1-lv_root on /var/lib/docker/btrfs type btrfs (rw,relatime,ssd,space_cache,subvolid=257,subvol=/@/var/lib/docker/btrfs)
/dev/mapper/vg1-lv_root on /mnt/snap type btrfs (rw,relatime,ssd,space_cache,subvolid=767,subvol=/@apt-snapshot-release-upgrade-bionic-2021-05-21_10:38:10)
/dev/mapper/vg1-lv_root on /mnt/sub/root-volume type btrfs (rw,relatime,ssd,space_cache,subvolid=5,subvol=/)

/home, /data and /local are not involved, and /mnt/snap is the snapshot i want to rollback.

root@pc65472:/boot# btrfs sub list /
ID 257 gen 44758165 top level 5 path @
ID 258 gen 44758165 top level 5 path @home
 ...
ID 767 gen 44757961 top level 5 path @apt-snapshot-release-upgrade-bionic-2021-05-21_10:38:10
ID 768 gen 44757961 top level 5 path @apt-snapshot-release-upgrade-bionic-2021-05-21_10:38:13
ID 769 gen 44757961 top level 5 path @apt-snapshot-release-upgrade-bionic-2021-05-21_10:38:46

Is it sufficient to change the the default subvolume with btrfs sub set-default to the snapshot and reboot ?
Do i need additionally to modify grub and fstab ?

Or just modify grub and fstab, let it point to the snapshot and reboot ?

What is with mounting the snapshot and rsync it to the current / ?
I think that's not possible in a running system which has / mounted.

In some documents i read to create a snapshot from the snapshot i want rollback to, if something goes wrong.

/boot is on a ext3-partition, it is not involved.

Bernd

-- 

Bernd Lentes 
System Administrator 
Institute for Metabolism and Cell Death (MCD) 
Building 25 - office 122 
HelmholtzZentrum München 
bernd.lentes@helmholtz-muenchen.de 
phone: +49 89 3187 1241 
phone: +49 89 3187 3827 
fax: +49 89 3187 2294 
http://www.helmholtz-muenchen.de/mcd 

Public key: 

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