How I purged zsys and lived to tell the tale

gistfile1.txt

You're going to need to snap your root according to zsys convention (just using a date won't work), like this: 

#!/bin/bash

DATE_HASH="$( date | cksum | cut -f1 -d' ' | tr -d '\n' | xargs -0 printf '%x\n' )"

zfs snapshot -r bpool@snap_"$DATE_HASH"_prepApt
zfs snapshot rpool@snap_"$DATE_HASH"_prepApt
zfs snapshot -r rpool/ROOT@snap_"$DATE_HASH"_prepApt
zfs snapshot -r rpool/USERDATA@snap_"$DATE_HASH"_prepApt

And you'll need to execute such a script before 'apt upgrade' from /etc/apt/apt.conf.d:

// Takes a snapshot of the system before package changes.
DPkg::Pre-Invoke {"[ -x /usr/local/sbin/snapPrepApt ] && /usr/local/sbin/snapPrepApt || true";};

And when you update your kernel from /etc/kernel/preinst.d like so:

#!/bin/sh
[ -x /usr/local/sbin/snapPrepApt ] && /usr/local/sbin/snapPrepApt || true

This seems to work with the initramfs/GRUB hooks which remain after you purge zsys.

@46cv8 what makes you think the experiment is defunct? (See OpenZFS on Ubuntu 24.04)

I've been using ZFS on a 22.04 desktop installation for about 2 years now. I would say it is not for the faint-of-heart.

Hey @fpga-guy , Sorry the wording I used was unnecessary. I removed it, then refreshed just now only to see your comment referencing my wording :) Awkwardling coincidental. I've been using ZoL with zsys since 20.04 first released, and generally it's ok. However of the two times I tried to rollback, I always ended up with mismatched root and user data sets, and ended up i other strange situations that required recovering from a hard disk image backups. My use of the wording defunct, was not appropriate, but was mainly to reflect the multitude of users who have experienced issues and the lack of continued development beyond upgrades for continued compatibility (of which I am grateful).

Unrelated to this GIST, but perhaps you might have had a similar issue and can share some wisdom.
After upgrading to 22.04 from 20.04 this January I ended up with duplicate userdata datasets, The old ones appear to be not mounted, but they are the ones that generating snapshots, meanwhile the new ones, are not generating snapshots but they are mounted.
I've lost almost all the benefit of running zsys for backups as I'm afraid to even attempt to do a rollback as I have no idea which of my userdata datasets would get used, and it might result in my losing a bunch of data like ubuntu/zsys#218
I am not sure how to tell zsys which of the two datasets it should use for backups, it seems to be mounting a different one than the one it seems to want to take snapshots of.

Here's what it shows as

zsysctl show --full
Name:               rpool/ROOT/ubuntu_zysz53
ZSys:               true
Last Used:          current
Last Booted Kernel: vmlinuz-6.8.0-45-generic
System Datasets:
 - bpool/BOOT/ubuntu_zysz53
 - rpool/ROOT/ubuntu_zysz53
 - rpool/ROOT/ubuntu_zysz53/srv
 - rpool/ROOT/ubuntu_zysz53/usr
 - rpool/ROOT/ubuntu_zysz53/var
 - rpool/ROOT/ubuntu_zysz53/usr/local
 - rpool/ROOT/ubuntu_zysz53/var/games
 - rpool/ROOT/ubuntu_zysz53/var/lib
 - rpool/ROOT/ubuntu_zysz53/var/log
 - rpool/ROOT/ubuntu_zysz53/var/mail
 - rpool/ROOT/ubuntu_zysz53/var/snap
 - rpool/ROOT/ubuntu_zysz53/var/spool
 - rpool/ROOT/ubuntu_zysz53/var/www
 - rpool/ROOT/ubuntu_zysz53/var/lib/AccountsService
 - rpool/ROOT/ubuntu_zysz53/var/lib/NetworkManager
 - rpool/ROOT/ubuntu_zysz53/var/lib/apt
 - rpool/ROOT/ubuntu_zysz53/var/lib/dpkg
 - rpool/ROOT/ubuntu_zysz53/var/lib/libvirt
User Datasets:
 User: root
 - rpool/USERDATA/root_ay5lx4
 User: me
 - rpool/USERDATA/me_ay5lx4
=== truncated ===

zsysctl machine show
Name:           rpool/ROOT/ubuntu_zysz53
ZSys:           true
Last Used:      current
History:        
  - Name:       rpool/ROOT/ubuntu_zysz53@autozsys_owqm41
    Created on: 2024-09-15 06:40:15
Users:
  - Name:    me
    History: 
     - rpool/USERDATA/me_ay5lx4@autozsys_9zrct9 (2024-09-16 17:20:27)
     - rpool/USERDATA/me_ay5lx4@autozsys_g3slmh (2024-09-16 16:20:14)
     - rpool/USERDATA/me_ay5lx4@autozsys_yss3gn (2024-09-16 15:50:54)
     - rpool/USERDATA/me_ay5lx4@autozsys_ybuc4b (2024-09-16 14:50:43)
     - rpool/USERDATA/me_ay5lx4@autozsys_s3ctfq (2024-09-16 13:50:32)
     - rpool/USERDATA/me_ay5lx4@autozsys_owqm41 (2024-09-15 06:40:15)
     - rpool/USERDATA/me_ay5lx4@autozsys_4t8vy5 (2024-02-08 13:23:19)
     - rpool/USERDATA/me_svq82i (0001-01-01 00:00:00)
  - Name:    root
    History: 
     - rpool/USERDATA/root_ay5lx4@autozsys_owqm41 (2024-09-15 06:40:15)
     - rpool/USERDATA/root_ay5lx4@autozsys_lc09rk (2024-05-23 06:06:31)
     - rpool/USERDATA/root_ay5lx4@autozsys_zj9059 (2024-05-22 06:45:25)
     - rpool/USERDATA/root_ay5lx4@autozsys_usa8oh (2024-05-15 06:04:33)
     - rpool/USERDATA/root_ay5lx4@autozsys_hpfi7t (2024-05-11 11:40:04)
     - rpool/USERDATA/root_ay5lx4@autozsys_4t8vy5 (2024-02-08 13:23:19)
     - rpool/USERDATA/root_svq82i (0001-01-01 00:00:00)


zfs list -r -o creation,space,mountpoint,mounted rpool/USERDATA
CREATION               NAME                         AVAIL   USED  USEDSNAP  USEDDS  USEDREFRESERV  USEDCHILD  MOUNTPOINT   MOUNTED
Mon Aug 24 14:26 2020  rpool/USERDATA                192G   231G        0B     96K             0B       231G  /            no
Mon Aug 24 14:29 2020  rpool/USERDATA/me_ay5lx4      192G   184G      245M    183G             0B         0B  /home/me     no
Thu Feb  8 17:24 2024  rpool/USERDATA/me_svq82i      192G  47.1G        0B   47.1G             0B         0B  /home/me     yes
Mon Aug 24 14:29 2020  rpool/USERDATA/root_ay5lx4    192G  44.9M      208K   44.7M             0B         0B  /root        no
Thu Feb  8 17:24 2024  rpool/USERDATA/root_svq82i    192G  1.73M        0B   1.73M             0B         0B  /root        yes

@46cv8 I did what was in my post and it worked, but I ended up installing 24.04 from scratch due to another issue unrelated. I followed the guide from https://github.com/Sithuk/ubuntu-server-zfsbootmenu

Thanks for the reply I think I understand after re-reading your comment afew times. I may attempt this after I do a full image backup. I should probably also try updating my kernel just to confirm that part of the snapshot process also works properly if I attempt it. Thanks again.

@46cv8 I did what was in my post and it worked, but I ended up installing 24.04 from scratch due to another issue unrelated. I followed the guide from https://github.com/Sithuk/ubuntu-server-zfsbootmenu

Thanks for the reply I think I understand after re-reading your comment afew times. I may attempt this after I do a full image backup. I should probably also try updating my kernel just to confirm that part of the snapshot process also works properly if I attempt it. Thanks again.

Great idea. Test failure scenarios, while having a full image backup. Hopefully that's good ha.

I managed to fix my issues with zsys so I'm keeping it for the time being. I posted an answer on a stackexchange thread that helped me resolve the issue. https://askubuntu.com/questions/1388997/zsys-commit-service-fails-with-couldnt-promote-dataset-not-a-cloned-filesy/1528760#1528760