Preparing for my first major upgrade (Kubuntu 25.04 to 25.10)

grahamperrin · October 11, 2025, 8:31am

I’m accustomed to major upgrades and ZFS boot environments with FreeBSD.

The step up to 25.10 will be my first major upgrade with Linux. I have a few basic questions, please ELI5.

GRUB

If I find a significant problem following the upgrade, will there be a GRUB option to boot an earlier kernel?

If so: will the userland work with the booted kernel?

ZFS

I can create a checkpoint of rpool before the upgrade.

https://openzfs.github.io/openzfs-docs/man/master/8/zpool-checkpoint.8.html

Should I also create a checkpoint of bpool?

Recovery

If I need to use a recovery mode for Kubuntu, will it be something like what’s described in this 2022 post about Ubuntu?

Fixing a failed upgrade to Ubuntu 22.04 LTS in recovery mode | Koen Vervloesem - Technology Writer

Background

https://mastodon.bsd.cafe/@grahamperrin/114640816892663471 (2025-06-07)

I chose Ubuntu (for KDE Plasma) because the installer provides root-on-ZFS. …

I also chose encryption when installing.

Thanks

ricktimmis · October 11, 2025, 8:46am

Hey Graham

Delighted you’re upgrading.
Grub, Yes Grub keeps previous kernels, you’ll need to boot with out the splash screen to access the menu → recovery mode

Checking pointing on a CoW filesystem makes sense, consider placing /home on a different volume if not already, as the upgrade doesn’t touch /home.

Recovery: Yes those steps in your post are correct (nice post btw). Also if you download the ISO onto a USB Key, then you’ve got a live boot to fix anything else.

Feel free to ask questions here, or catch up with us on Matrix at #kubuntu:matrix.org.

ttfn.
Rick

grahamperrin · October 11, 2025, 4:49pm

I wrote kubuntu-25.10-desktop-amd64.iso to a USB memory stick, booted, both displays work in live mode, so I don’t expect a problem with the upgrade.

Results of hardware probes:

LUKS, misunderstood

I sped through a few manual pages, with 25.10 in live mode, but could not figure out how to decrypt the LUKS volume where rpool is stored. I booted 25.04 to search the web and save results, much of what I found was way off. A handful, in chronological order:

https://askubuntu.com/q/653408/25036 – boot - Mounting encrypted LUKS partition from Live CD - Ask Ubuntu
https://unix.stackexchange.com/q/399620/13260 – ubuntu - How to decrypt a hard drive with LUKS encryption? - Unix & Linux Stack Exchange
https://ubuntu-mate.community/t/how-to-decrypt-disk-on-linux/19140 – How to decrypt disk on Linux? - Support & Help Requests - Ubuntu MATE Community
https://www.reddit.com/r/linux4noobs/comments/1jckz9u/comment/mi36pl6/ – ScratchHistorical507 comments on Could I decrypt a LUKS encrypted drive without booting into it?

I took a hint from https://ubuntu-mate.community/t/how-to-decrypt-disk-on-linux/19140/4 (2019), ignoring the preceding blurb about deleting partitions:

grahamperrin@mowa219-gjp4 ~> lsblk --fs /dev/sda
NAME           FSTYPE     FSVER LABEL      UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
sda                                                                                            
├─sda1         vfat       FAT32            A6F3-228F                                 1G     1% /boot/efi
├─sda2         zfs_member 5000  bpool      4044919440379282905                                 
├─sda3                                                                                         
│ └─dm_crypt-0 swap       1     dm_crypt-0 0df3b995-50bc-4780-828a-40d39e21e58c                [SWAP]
└─sda4         zfs_member 5000  rpool      2926510480119158627                                 
grahamperrin@mowa219-gjp4 ~> sudo cryptsetup isLuks /dev/sda4
grahamperrin@mowa219-gjp4 ~ [1]> lsblk /dev/sda
NAME           MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
sda              8:0    0 931.5G  0 disk  
├─sda1           8:1    0     1G  0 part  /boot/efi
├─sda2           8:2    0     2G  0 part  
├─sda3           8:3    0     8G  0 part  
│ └─dm_crypt-0 252:1    0     8G  0 crypt [SWAP]
└─sda4           8:4    0 920.5G  0 part  
grahamperrin@mowa219-gjp4 ~>

So, I guess that (in live mode) I’ll need to decrypt /dev/sda4.

Taking a hint from something that I don’t want (https://wiki.archlinux.org/title/Resizing_LVM-on-LUKS#Boot_and_setup), for something that I might want:

cryptsetup luksOpen /dev/sda4 cryptdisk

Will that be correct?

grahamperrin · October 11, 2025, 4:59pm

From ScratchHistorical507 comments on Could I decrypt a LUKS encrypted drive without booting into it?:

… You can usually use the preinstalled disk managment tool to decrypt the partitions. …

I tried KDE Partition Manager with 25.10 in live mode, I saw nothing related to encryption or decryption (and KHelpCenter does not suggest using the app).

Similarly: nothing apparent in GParted.

In retrospect, I might have been wrong to assume that the partition is LUKS-encrypted.

grahamperrin · October 11, 2025, 5:36pm

OK, I had things back-to-front. I wrongly assumed that LUKS came first (because on FreeBSD, it’s necessary to decrypt at the GELI level before a pool on the decrypted device can be imported).

So: I could import a pool with an altroot e.g.

sudo zpool import -f -R /tmp/altroot rpool

– but then, I could not mount the ZFS file systems.

I found a helpful answer here:

encryption - How to mount an encrypted Ubuntu 20.10 ZFS file system from an Ubuntu live CD? - Ask Ubuntu

grahamperrin · October 12, 2025, 5:30pm

Successful use of the decrypted data, with 25.10 in live mode, although I don’t understand why the pool will not export:

no response to sudo zpool export rpool

kubuntu@kubuntu:~$ zfs list
NAME                                               USED  AVAIL  REFER  MOUNTPOINT
rpool                                              408G   484G   192K  /tmp/altroot
rpool/ROOT                                        25.2G   484G   192K  none
rpool/ROOT/ubuntu_v0hpws                          25.2G   484G  10.1G  /tmp/altroot
rpool/ROOT/ubuntu_v0hpws/srv                       192K   484G   192K  /tmp/altroot/srv
rpool/ROOT/ubuntu_v0hpws/usr                      11.8M   484G   192K  /tmp/altroot/usr
rpool/ROOT/ubuntu_v0hpws/usr/local                11.6M   484G  11.6M  /tmp/altroot/usr/local
rpool/ROOT/ubuntu_v0hpws/var                      15.1G   484G   192K  /tmp/altroot/var
rpool/ROOT/ubuntu_v0hpws/var/games                 192K   484G   192K  /tmp/altroot/var/games
rpool/ROOT/ubuntu_v0hpws/var/lib                  13.0G   484G  12.7G  /tmp/altroot/var/lib
rpool/ROOT/ubuntu_v0hpws/var/lib/AccountsService   212K   484G   212K  /tmp/altroot/var/lib/AccountsService
rpool/ROOT/ubuntu_v0hpws/var/lib/NetworkManager    384K   484G   384K  /tmp/altroot/var/lib/NetworkManager
rpool/ROOT/ubuntu_v0hpws/var/lib/apt               113M   484G   113M  /tmp/altroot/var/lib/apt
rpool/ROOT/ubuntu_v0hpws/var/lib/dpkg              112M   484G   112M  /tmp/altroot/var/lib/dpkg
rpool/ROOT/ubuntu_v0hpws/var/log                  2.08G   484G  2.08G  /tmp/altroot/var/log
rpool/ROOT/ubuntu_v0hpws/var/mail                  192K   484G   192K  /tmp/altroot/var/mail
rpool/ROOT/ubuntu_v0hpws/var/snap                 10.5M   484G  10.5M  /tmp/altroot/var/snap
rpool/ROOT/ubuntu_v0hpws/var/spool                 868K   484G   868K  /tmp/altroot/var/spool
rpool/ROOT/ubuntu_v0hpws/var/www                   192K   484G   192K  /tmp/altroot/var/www
rpool/USERDATA                                     383G   484G   192K  none
rpool/USERDATA/home_dz7uxs                         383G   484G   383G  /tmp/altroot/home
rpool/USERDATA/root_dz7uxs                        27.2M   484G  27.2M  /tmp/altroot/root
rpool/keystore                                    38.8M   484G  16.5M  -
rpool/var                                         1.98M   484G   192K  /tmp/altroot/var
rpool/var/lib                                     1.79M   484G   192K  /tmp/altroot/var/lib
rpool/var/lib/docker                              1.61M   484G  1.61M  /tmp/altroot/var/lib/docker
kubuntu@kubuntu:~$ sudo cryptsetup open /dev/zvol/rpool/keystore zfskey
Enter passphrase for /dev/zvol/rpool/keystore: 
kubuntu@kubuntu:~$ sudo cat /media/kubuntu/keystore-rpool/system.key | sudo zfs load-key -L prompt rpool
kubuntu@kubuntu:~$ sudo zfs mount -a
kubuntu@kubuntu:~$ mount | grep zfs | sort
/dev/mapper/zfskey on /media/kubuntu/keystore-rpool type ext4 (rw,nosuid,nodev,relatime,errors=remount-ro,stripe=8192,uhelper=udisks2)
rpool/ROOT/ubuntu_v0hpws on /tmp/altroot type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/srv on /tmp/altroot/srv type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/usr/local on /tmp/altroot/usr/local type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/games on /tmp/altroot/var/games type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/lib on /tmp/altroot/var/lib type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/lib/AccountsService on /tmp/altroot/var/lib/AccountsService type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/lib/NetworkManager on /tmp/altroot/var/lib/NetworkManager type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/lib/apt on /tmp/altroot/var/lib/apt type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/lib/dpkg on /tmp/altroot/var/lib/dpkg type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/log on /tmp/altroot/var/log type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/mail on /tmp/altroot/var/mail type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/snap on /tmp/altroot/var/snap type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/spool on /tmp/altroot/var/spool type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/ROOT/ubuntu_v0hpws/var/www on /tmp/altroot/var/www type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/USERDATA/home_dz7uxs on /tmp/altroot/home type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/USERDATA/root_dz7uxs on /tmp/altroot/root type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
rpool/var/lib/docker on /tmp/altroot/var/lib/docker type zfs (rw,nodev,relatime,xattr,posixacl,casesensitive)
kubuntu@kubuntu:~$ ls -hl /tmp/altroot/home/grahamperrin/Desktop/2025-09-*
-rw-rw-r-- 1 kubuntu kubuntu 423K Sep  6 18:55 '/tmp/altroot/home/grahamperrin/Desktop/2025-09-06 20-37 pkg issue 2475, 257 candidates, success.txt'
-rw-rw-r-- 1 kubuntu kubuntu  19K Sep  7 12:51  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-07 13- killing at 552 of 1309 (discount) during a major upgrade with 1 GB memory.png'
-rw-rw-r-- 1 kubuntu kubuntu 129K Sep 16 21:30  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-16 22-29 KDE Plasma, FreeBSD 16.0-CURRENT.png'
-rw-rw-r-- 1 kubuntu kubuntu  39K Sep 17 04:46  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-17 05-44 FreeBSD 15.0-ALPHA2 zpool scrub of a read-only pool.png'
-rw-rw-r-- 1 kubuntu kubuntu  90K Sep 17 05:29  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-17 06-29 Phoronix, unable to type a comment.png'
-rw-rw-r-- 1 kubuntu kubuntu 125K Sep 17 22:04  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-17 got on FreeBSD 15.0-ALPHA2 requires libretls.png'
-rw-rw-r-- 1 kubuntu kubuntu 712K Sep 20 13:30  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-20 14-27 Firefox, pkgbase.png'
-rw-rw-r-- 1 kubuntu kubuntu  59K Sep 20 13:43  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-20 14-42 Firefox bars.png'
-rw-rw-r-- 1 kubuntu kubuntu 3.0M Sep 21 06:48  /tmp/altroot/home/grahamperrin/Desktop/2025-09-21.06-21.typescript.txt
-rw-rw-r-- 1 kubuntu kubuntu  93K Sep 22 04:43 '/tmp/altroot/home/grahamperrin/Desktop/2025-09-22 05-38 pkg issue 2522 comment 3316711750 tail of typescript.txt'
-rw-rw-r-- 1 kubuntu kubuntu  69K Sep 22 20:43  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-22 21-21 ALPHA3 userland upgrade failed.png'
-rw-rw-r-- 1 kubuntu kubuntu  44K Sep 22 20:50  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-22 21-50 single user mode broken.png'
-rw-rw-r-- 1 kubuntu kubuntu  73K Sep 27 13:50  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-27 14-49 ignorant troublemaker.png'
-rw-rw-r-- 1 kubuntu kubuntu  54K Sep 27 23:58  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-28 00-58 118 to be removed.png'
-rw-rw-r-- 1 kubuntu kubuntu  55K Sep 28 00:00  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-28 01-00 proceeding.png'
-rw-rw-r-- 1 kubuntu kubuntu  69K Sep 28 00:16  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-28 01-15 -uY after upgrading the kernel alone.png'
-rw-rw-r-- 1 kubuntu kubuntu 320K Sep 28 10:30  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-28 11-30 swap off, reinstallation failed.png'
-rw-rw-r-- 1 kubuntu kubuntu  11K Sep 28 01:33  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-28 ALPHA4, base, the complete base.png'
-rw-rw-r-- 1 kubuntu kubuntu  30K Sep 28 05:46  '/tmp/altroot/home/grahamperrin/Desktop/2025-09-28-06-40 15.0-ALPHA4 REPOS_DIR.png'
kubuntu@kubuntu:~$ zpool export rpool
cannot unmount '/tmp/altroot/var/www': permission denied
kubuntu@kubuntu:~$ sudo zpool export rpool
^T^C

The tail:

kubuntu@kubuntu:~$ sudo zpool export rpool
^T^C

no response to Control-T or Control-C.

In a separate Konsole tab:

kubuntu@kubuntu:~$ sudo lsof /tmp/altroot
lsof: WARNING: can't stat() fuse.portal file system /run/user/1000/doc
      Output information may be incomplete.
kubuntu@kubuntu:~$ sudo lsof /tmp/altroot
lsof: WARNING: can't stat() fuse.portal file system /run/user/1000/doc
      Output information may be incomplete.
kubuntu@kubuntu:~$ mount | grep zfs
/dev/mapper/zfskey on /media/kubuntu/keystore-rpool type ext4 (rw,nosuid,nodev,relatime,errors=remount-ro,stripe=8192,uhelper=udisks2)
kubuntu@kubuntu:~$ zpool status -v
  pool: rpool
 state: ONLINE
  scan: scrub repaired 0B in 00:18:38 with 0 errors on Sat Oct 11 23:42:41 2025
config:

        NAME                            STATE     READ WRITE CKSUM
        rpool                           ONLINE       0     0     0
          wwn-0x5002538f42b2daed-part4  ONLINE       0     0     0

errors: No known data errors
kubuntu@kubuntu:~$

mcarans · November 2, 2025, 10:48pm

Glad it worked for you. I have a problem with ssh unfortunately.