Application - DKMS Uploader - John Cabaj

Community Ubuntu Developer Membership
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I, John Cabaj, am applying for Ubuntu DKMS Uploader.

Contact Information

Name John Cabaj
Launchpad Page https://launchpad.net/~john-cabaj
Matrix username @john-cabaj:matrix.org
Email john-cabaj@ubuntu.com

I am applying for DKMS Uploader because:

  • I’ve been the ZFS maintainer for Ubuntu for 1.5 years. With our goal of landing the latest upstream kernels in the development releases, ZFS support for the kernel is paramount. It’s become increasingly difficult to maintain this while requiring others to sponsor my work.
  • Cloud partners that I work with continually ask for support for new DKMS packages.
  • The number of DKMS Uploaders in the Kernel Team is frighteningly low, and I’d like to ease the burden on our Archive Admins and Core Devs by being able to sponsor more of these packages and allow them to focus on other tasks.

Who I am

My name is John Cabaj. I’ve been with Canonical for about 4 years, with the entirety of my time spent in the Kernel Team, working with cloud providers specifically. In my time with the team, I started working to support the IBM Cloud partnership. Additionally, I helped out with the Google Cloud partnership for a time, before moving over to the Azure Cloud, where I’m the lead Kernel Engineer working across all linux-azure (and variant) kernels (alongside IBM).

A couple of years ago, an opportunity arose to expand my knowledge of Debian packaging when the DKMS maintainer left Canonical. Consequently, there was no one to continue the upkeep of ensuring ZFS would build properly against devel release kernels, as well as providing necessary patches back to earlier LTS releases. I thought it would be an interesting opportunity to deep-dive further into the distribution, and have been maintaining ZFS ever since. I’ve also had the opportunity to pursue many other DKMS uploads for HWE kernel releases, including the majority of DKMS packages required to build for the Noble HWE 6.11 and 6.17 kernel releases.

In addition to this, I enjoy working on the Ubuntu Asahi community distribution. I took over as the lead kernel engineer starting the the Mantic 23.10 release, providing almost all updates to the kernel users install when they want to run Ubuntu on Apple Silicon.

I’m currently based in the Madison, Wisconsin area. I received a Master’s Degree in Computer Engineering from the University of Wisconsin-Madison in 2015. I hold Bachelor’s Degrees in both Computer Engineering and Computer Science from the University of Wisconsin-Madison as well. Outside of work, I enjoy most sports, my favorite being ice hockey.

My Ubuntu Story

My first experience with Linux was during university around 2010, using Ubuntu 10.04 (or thereabouts) on a Dell XPS M1730. I recall the experience out of the box was promising, though WiFi drivers back then were a bit more of a hassle (can’t access the internet, and can’t download the driver because you can’t access the internet). I then installed Ubuntu on a Dell Netbook (remember those?) so I could avoid going to the school computer labs to do my OS coursework.

When I graduated and joined a local startup, I primarily used Ubuntu 14.04 and dove into bash scripting various portions of a machine learning pipeline. I then joined a medical device company which was primarily using CentOS. There I worked with the RT kernel (via the PREEMPT_RT patchset) primarily writing user-space applications running as a systemd service before joining Canonical in 2022.

Examples of my work / Things I’m proud of

Things I could do better

I would like to continue to use my experience in kernel packaging, as well as DKMS, to expand more outside just the kernel.

Plans for the future

General

As we’re getting shorthanded in DKMS Uploaders in the Kernel Team, my immediate goal would be to take an active role in sponsoring DKMS packages from other contributors in the Kernel Team or otherwise. Additionally, I plan to increase my throughput of DKMS uploads as my uploads won’t require sponsorship anymore. I suspect this will allow me to contribute much more quickly to subsequent HWE kernel rolls.

What I like least in Ubuntu

One of the things I like least is also a great strength of the distribution: Ubuntu has so many great engineers working on so many great pieces of software - sometimes it’s hard to settle on the right tool to use for the job when there are constantly better versions available. I still use pull-lp-sourcewhen there are other means available now. I’ve been meaning to switch a bit more to git-ubuntu, but sometimes getting something out necessitates the familiar path.

Purely as more of a user, I don’t like how my laptop sometimes decides not to suspend when I’d like it to. Also my brand new flashy webcam seems to freeze and and work generally worse than the one that comes with my laptop. I could probably look into these more myself (if I found the time), and be the change that I want to see.

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Ubuntu Developer Membership Board Agenda
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I have recently sponsored some zfs-linux security updates for John. While I don’t have enough experience with John to fully endorse this application, I would like to mention that the updates were well done, and the experience was a positive one. Looking at his history of uploaded packages, a lot of them do contain dkms modules, so I believe he does appear to have the required knowledge to tackle the complexity and subtleties of the dkms package.

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I endorse John for DKMS upload rights.

Sponsoring feedback

I have sponsored 22 uploads for John, almost all of them DKMS packages, and they fall into two groups.

The Noble 6.14 HWE DKMS enablement (May 2025). When the 6.14 HWE kernel came to Noble, a long tail of DKMS packages stopped building against it. John went through them one by one: he filed a bug for each FTBFS, prepared a fix, and set up the SRU. In about a week I sponsored 17 of them:

These packages don’t have much in common: out-of-tree wireless and modem drivers, a display driver, filesystems, tracing, networking. Each one broke in its own way against the new kernel APIs, and John had to understand each module well enough to fix it without breaking the older kernels still shipped in Noble. The uploads were consistent, and the SRU paperwork was in order.

ZFS on the development kernels. I work on the Ubuntu development kernel that tracks the latest mainline -rc, so I depend directly on zfs-linux building against whatever kernel comes next. John keeps it building. I sponsored several of these uploads:

Specific experiences of working together

My goal is to ship the latest upstream kernel in the development release. With that goal, ZFS support isn’t optional: a new kernel can’t land if zfs-linux doesn’t build against it. John has carried this work since the previous DKMS maintainer left, which is usually before upstream OpenZFS officially supports the new kernel. He tracks the relevant upstream fixes, backports them, and sends fixes to OpenZFS where needed. Because he doesn’t have upload rights, every one of those uploads has waited on a sponsor. That delay directly affects how quickly we can move the development release to a new kernel.

His broader record points the same way. He has had nearly 500 sponsored uploads since 2022 across every supported series from focal to resolute. Those include 29 zfs-linux uploads, the Noble 6.17 HWE DKMS work (VirtualBox included), and the Azure and IBM kernels he owns.

Areas of improvement and next steps

I see no blockers. As he says in his application, the next step is to broaden beyond kernel-adjacent packaging. Sponsoring DKMS uploads for others is a good way to start, and the kernel team needs more people who can do that.

I trust John to handle DKMS upload rights carefully and responsibly, and I think both the kernel team and the archive would benefit from him having them.

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I endorse John for DKMS upload rights.

I’ve sponsored 12 uploads for him, mainly zfs-linux and some other dkms updates. Most of these were for the development series, but two were SRU’s which follow a different workflow. The first one required some updates to the test case, but the second one had everything from the start.

He’s actively in touch with ZFS upstream about issues that we see with (especially) rc-kernels, so having him being able to upload it (and build-fix DKMS updates in general) directly would be a great benefit to the kernel team and Ubuntu in general.

After working on the team for four years I believe he’s also able to mentor other prospective DKMS uploaders in the future.

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