recovering system after upgate ruined graphics

[oldgeek]

I am using the 24.04 lts with btrfs file system. Yesterday an upgrade through Discover seemed to have eliminated my 470 driver for Nvidia GEForce 730 graphics card,, making it use only a lower resolution. So I decided to roll back to the previous snapshot I took on Monday for @. This is what I did. First, I used the mv command to change the subv name from /mnt/@ to /mnt/@_new. Then using the send command (btrfs send /mnt/snapshots/@_260602-194244_ro | btrfs recdeive /mnt). That took awhile. When done, I switched the subv from read only to read-write, then changed the name using the move command to /mnt/@. I did not delete the /mnt//@_new subv. Then I rebooted. Unfortunately, I could not get to the login screen. Can anyone help me? I suspect I did something wrong in the swend command,, since I haven't done this in quite awhile.

[jlittle]

The name of the root volume should be just @. Did you mount the btrfs top level on /mnt? If not, then /mnt/@ is not @. IME mounting the top level on /mnt has lead to my being confused and setting up conflicts; I prefer using a name like /mnt/top or /top.

The send receive may have been unnecessary; you could have just snapshotted /mnt/snapshots/@_260602-194244_ro onto /mnt/@, unless /mnt/snapshots is on another fs.

At this point I hope you've got a live USB, or another install you can boot to. The next step would be to boot to a live USB, mount the main install to somewhere like /mnt/top, and investigate. Perhaps posting an ls of that top level here.

[oldgeek]

I was able to get back to my post-update setup (with the low resolution 1024x786, if I remember right), so at least it's working again, though not how I want it. Remembering vaguely the updates,they included changes to the 470 driver, the 535 driver and the X-org graphic system, which I had been using. After the update, none of the Nvidia drivers are available on the .driver manager in Settings, only the manual one, whatever that is. It doesn't allow me to change the resolution either. Also, I discovered the post-update system is using Wayland! I don't know how that happened, as my previous setup didn't even allow me to switch to Wayland from the login screen. Tomorrow I will try again to use my snapshot to function as @ and will report the results. But it would be nice if somebody could tell me what Kubuntu did to my LTS in their update. It seems odd that something of this nature would be allowed to be installed on on an LTS distro, causing it to change the graphics look completely. Thanks for your help, Mr. Little. I may have to ask you more about what you mean by the top level on /mnt and how I can find out if my setup is correct.

[jlittle]

In my first use of btrfs, I was confused by the difference between the btrfs root, subvol=/ and the Linux root /, they're not the same. In a standard install the Linux root is mounted on the btrfs /@. There's a line in /etc/fstab looking something like

UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /   btrfs  subvol=@   0  1

I suggest, adjusting the x's to match

sudo mkdir -p /mnt/top
sudo mount UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /mnt/top -o subvol=/
cd /mnt/top
ls

You should see @ and @home there. (Note that btrfs lets you mount many places in one btrfs, and the same place several times.)

When I release upgraded from 25.04 to 25.10, wayland was imposed without asking me, and stuff broke. I had to

sudo apt install plasma-session-x11

to be able to select X11 on the login screen. I wonder if that's happened to you.

[claydoh]

Easy btrfs management for this sort of thing: use Timeshift. Make a selection, a few clicks, done, reboot.
For emergency use, it can be installed in a live *buntu/Mint OS

Even from the command line in Recovery mode or a tty, using it is almost as simple.

$ sudo timeshift --restore
Mounted '/dev/nvme1n1p2' at '/run/timeshift/610393/backup'
btrfs: Quotas are not enabled

Select snapshot:

Num Name Tags Description
------------------------------------------------------------------------------
0 > 2026-05-27_21-12-04 O W M This is NOT the original start point, I forgetted that
1 > 2026-05-31_08-10-52 D
2 > 2026-05-31_22-22-39 B
3 > 2026-06-01_08-10-51 B D
4 > 2026-06-02_11-00-01 D Let's not do that again.
5 > 2026-06-03_08-11-15 B
6 > 2026-06-03_11-00-01 D
7 > 2026-06-03_22-00-01 W
8 > 2026-06-04_08-10-52 B
9 > 2026-06-04_11-00-01 D
10 > 2026-06-04_11-55-03 B
11 > 2026-06-05_12-00-02 D

Enter snapshot number (a=Abort, p=Previous, n=Next):