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I adapted a ZoL guide for putting Ubuntu Server 14.04 on ZFS root for 18.04 Bionic Beaver and desktop installations: http://vlog.averyfreeman.com/doku.php/ubuntu.18.04.desktop.on.zfs

I'm trying to make sure I have all of the information correct, I've run into a couple issues I'm not sure how to answer:

Does ZFS support in Ubuntu for generic kernels require the zfs-dkms package, or is just zfs-initramfs enough? (Do generic kernels in Ubuntu have kABI extensions?)

If anyone actually follows it, I'd like them to have a bootable system after a kernel upgrade! :)

Also, is there a way to prevent having to invoke # zfs import -f rpool and reboot after boot of updated kernel?

  • I think that zfs-initramfs is not necessary for generic kernels (I never needed it and ZFS seems to be working, it might have a purpose, though). zfsutils-linux is probably necessary in any case where one wants to do any ZFS administration. – Karl Richter Aug 24 '18 at 6:24
  • Maybe zfs-dkms provides an update functionality? However, important updates for the same Ubuntu version would probably justify to release a kernel update. – Karl Richter Aug 24 '18 at 6:35
  • What does zfs import -f rpool do? Can you simply have a script run automatically every boot and check if it's been run already? if yes do nothing, if no then run it? The script might reside in /etc/rc.local or another place. – WinEunuuchs2Unix Aug 25 '18 at 18:33
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    Your link generates "access denied" message. – WinEunuuchs2Unix Aug 26 '18 at 1:51
  • I am quite confused to what you want to achieve - the "official" Ubuntu 18.04 Root on zfs guide is github.com/zfsonlinux/zfs/wiki/Ubuntu-18.04-Root-on-ZFS, updated just 8 days ago. – emk2203 Aug 30 '18 at 8:54
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From Ubuntu Wiki ZFS:

ZFS

Summary

ZFS is a combined file system and logical volume manager designed and implemented by a team at Sun Microsystems led by Jeff Bonwick and Matthew Ahrens. Its development started in 2001 and it was officially announced in 2004. In 2005 it was integrated into the main trunk of Solaris and released as part of OpenSolaris. Currently, as of January 2015, it is native to Solaris, OpenSolaris, OpenIndiana, illumos, Joyent SmartOS, OmniOS, FreeBSD, Debian GNU/kFreeBSD systems, NetBSD, OSv and supported on Mac OS with MacZFS.

The name "ZFS" originally stood for "Zettabyte File System". Currently it can store up to 256 ZiB (zebibytes).

Installing ZFS on Ubuntu

The ZFS filesystem is available for Ubuntu as either a FUSE module or a native kernel module. The kernel module is provided by default. To install the user-level tools, simply install:

sudo apt install zfsutils-linux 

For all current versions from 16.04 onward.

In addition to be able to have ZFS on root, install:

sudo apt install zfs-initramfs 

No where is it mentioned that zfs-dkms is a prerequisite.


kABI

kABI is the Kernel Application Binary Interface. It doesn't change very often but when it does all programs must share the same version.

Tracking ABI/API changes

From the ABI Labratory we can see the last changes were on June 4, 5 and 6th, 2018:

Linux ABI changes.png

We can see the Linux Kernel numbers revised in June 2018 were:

  • 4.14.48, 4.9.107 and 4.4.136 all 6 year LTS kernels

The corresponding Ubuntu Kernel version numbers were probably:

We need to upgrade Linux Kernels when new hardware support or bug fixes to existing hardware are released. When an ABI/API change is involved the Ubuntu kernel may or may not work. Even if an ABI/API change doesn't take place the Ubuntu Kernel may still break for some people for other reasons.

If you have a generic Ubuntu Kernel and a Linux Mainline kernel after June 2018 in this example, they would both share the same kABI.

  • After you deleted your previous answer, my comments are gone :(. I try to remember them all. First, some new notes: It seems unclear whether ZFS FUSE is maintained or not. It has seen some commits, however has no project homepage. What's the effect of installing zfs-dkms (it can still be installed although it's not prerequisite)? You mentioned excellent documentation in your previous answer, can you link it here, please? Please link the ZFS on Root instructions on the GitHub wiki. The summary is unnecessary as anyone who is interested knows what ZFS is. – Karl Richter Aug 29 '18 at 8:17
  • There're more questions by the OP: Do generic kernels in Ubuntu have kABI extensions? Is there a way to prevent having to invoke zfs import -f rpool and reboot after boot of updated kernel? – Karl Richter Aug 29 '18 at 8:19
  • @KarlRichter I've added kABI information. – WinEunuuchs2Unix Aug 30 '18 at 10:45

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