The Kdenlive team is happy to announce the release of version 25.12.0, just in time for the holiday season. For this release, we concentrated on improving the user experience. Many of these changes were discussed during our very productive Berlin sprint last September, where the team met for three days of brainstorming.

Interface and Usability

Docking System

We introduced a new, more flexible docking system, allowing you to group the widgets you want together or easily show/hide them on demand. Each layout is now saved in its own file, opening the possibility for sharing. It is also now saved inside the project file, so when reopening a project the layout used when saving it is loaded and you are immediately ready to continue where you left off editing! The downside is that existing layouts are not compatible, so that you will need to recreate your custom layouts.

Welcome Screen

We introduced a Welcome Screen to improve the experience for new users, and add some handy shortcuts for everyone. With your feedback this will evolve in the future.

Along with the Welcome Screen, we introduced a vertical layout and optional safe areas to improve editing of 9:16 videos.

Menu Restructuring

Part of a long running discussion in the team, the menus were re-organized to make them more intuitive. Our long-time users may be confused initially (hopefully not for long, though), but we tried to follow some of the conventions in the professional editing world. For example, we regrouped all file related actions like Render and the Project Settings in the File menu. There might be a few adjustments in the upcoming releases, but the most important changes are in.

Thanks to users and translators feedback, we were able to fix several parts of the user interface that were not picked up properly for translation, making Kdenlive easier to use in your native language.

Monitor

We revamped the monitor view of audio, with a minimap on top allowing to intuitively zoom parts of the audio. (audio monitor)

Markers

For consistency and to avoid confusion, we renamed timeline guides to markers, since the term guide was used interchangeably and therefore confusing, and they were in fact markers for a sequence clip. Markers can now have a duration that is shown in the timeline, and can be dragged in the timeline from the Markers list.

Other Highlights

Major Bug Fixes

• We fixed more than 15 crash reports
• Windows: Fix render failure when user name contains special characters
• Fix project corruption when copy-pasting a sequence or project file between projects

Packaging

• We fixed the VAAPI support in AppImage, allowing for faster decoding and render time
• Several updates made it into our binaries, like Qt 6.10.1 and FFmpeg 8.0

Last Minute Fixes

Several fixes that will be in the next release have already been included in the 25.12.0 binaries available on kdenlive.org. If you installed Kdenlive from your Linux distro, you will get those fixes with version 25.12.1 (release scheduled for January 2026).

Give back to Kdenlive

Releases are possible thanks to donations by the community. Donate now!

Need help ?

As usual, you will find very useful tips in our documentation website. You can also get help and exchange your ideas in our Kdenlive users Matrix chat room.

Get involved

Kdenlive relies on its community, your help is always welcome. You can contribute by :

• Helping to identify and triage bugs
• Contribute to translating Kdenlive in your language
• Promote Kdenlive in your local community

For the full changelog continue reading on kdenlive.org.

This is a effectively a guest blogpost where I, as usual, take the credit for the work someone else has done.

Last year ago set out making a home automation <--> Desktop Linux bridge over the Christmas holidays.

The idea is that if you're using home automation your PC that you're in front of has a lot of important information that can be used for adjusting automations; are you in a call, are your headphones on, and so on. I made a small daemon, named Kiot (derived from "KDE Internet of Things") that exposes this information about your PC to Home Automation software, like Home Assistant.

It worked well enough for all my use-cases, so after a bit of initial buzz and a few drive-by fixes it fell to the wayside whilst I worked on other things.

In the last month it got a new contributor, Odd Østlie (TheOddPirate) who has been like a rocket ship of new features; and a bit of a community with another member being active in testing and feedback.

We now track and expose:

• bluetooth

• audio devices, volume control and selection

• battery states for laptops and wireless peripherals

• gamepad detection

• active window information

• media player/mpris connection

With more integrations in pull requests.
There's also the start of a configuration UI, so there's no messing about with configuration files.

I'll do another post once we've made a 0.1 and a flatpak, but if you're interested in KDE + home automation, go check out his work at https://github.com/davidedmundson/kiot .

Last weekend I attended this year's edition of the KDE PIM Sprint which, this time, took place in Paris.

I arrived in Paris around 1 p.m. and first walked from Gare du Nord to the Île de la Cité to have a look at the reconstructed roof of Notre Dame. Then I checked in at my hotel and after a brief rest I went to the sprint venue, the office of enioka. There I was greeted by one of our hosts for the weekend and by a few KDE PIMsters who had already taken over the meeting room.

After firing up my computer, KMail complained that it couldn't access one of my IMAP accounts. The error said "authentication failed" and a second error message claimed that access to KWallet (which stores the passwords of the IMAP accounts) was denied. Using the website of the mail provider I verified that my credentials still work. Adding the IMAP account a second time didn't help. Still the same errors. And a look at KWallet also didn't give me a clue why it should deny access to the password of one of my IMAP accounts when two other IMAP accounts worked. Since access to this IMAP account wasn't that important during the KDE PIM sprint I decided not to waste more time on this problem. This proved to be a good decision because once I was back at home the account magically worked again. I blame weird security measures by the email provider.

In the meantime more people had arrived and we went for dinner. Afterward we went back to the venue and, now that most people were there, we went over the list of topics from last year's KDE PIM Sprint. Some progress has been made since the last sprint but many topics didn't see much work done. Any and all help is welcome!

Originally I planned to look into a bug that's been haunting me for some time: KMail shows seemingly random counts of unread messages in the folder list that have little to do with the actual number of unread messages in those folders. Because I'm using the latest stable versions of almost all KDE software (as provided by openSUSE Tumbleweed) I started to build the release/25.12 branch of KMail and its 30+ KDE PIM dependencies. This took the rest of Friday evening and part of Saturday morning. Shortly before midnight we called it a day.

On Saturday morning, after a joint breakfast in the office, we discussed a few more topics from our agenda. After that I decided to scratch my original plan and, instead, to help with making the KMime library fit for becoming a KDE Framework. I created a few MRs to replace the usage of bool parameters in the API with enums. Then I looked into adapting the users of KMime to the new API. Unfortunately, this proved more painful than expected because KDE PIM does not only depend on the master branch of everything else in KDE PIM (which I was very well aware of) but a lot of the KDE PIM projects also depend on the master branch of the ktextaddons library which is a kind of intermediate library between KDE Frameworks and KDE PIM with its own release schedule. For many of the KDE PIM projects I could simply lower the required version of ktextaddons to the latest stable release (as shipped by Tumbleweed), but for pimcommon this hack didn't work anymore because it used a new header from ktextaddons master. By then it was already Sunday afternoon and anyway time for me to pack my stuff.

On my way to Gare du Nord I passed by Sacré Cœur on Montmartre where to my surprise a choir of Santa Clauses and Santa Claudettes was performing French Christmas songs.

In conclusion, I got more useful work done during this sprint than during some other sprints, although the dependency requirements of KDE PIM annoy me a lot. I've been involved in KDE PIM for 25 years now although, admittedly, I rarely contribute to it in my spare time since I started to code for a living. To a large part the reason for this is that it would cost way too much of my spare time to build all of KDE PIM all of the time.

Thanks to enioka for hosting us and to Kevin for organizing the sprint. And many thanks to those of you donating to KDE which makes these sprints possible.

Welcome to the November 2025 development and community update.

Development Report

5.2.14 Released

One last bugfix release in the 5.2 series, 5.2.14 is out. This version once again features many fixes for Android and touch input, but that's not all! The Color Sampler's preview has a new round default look, and macOS users can now view .kra thumbnails in Finder again. Read more in the dedicated blogpost and stay up up-to-date.

Text Rework Progress

Development of 5.3.0 is now in feature freeze, meaning no more features will be added before release. This includes the Text Tool, marking the end of a long phase of development for Wolthera, code reviewer Dmitry, and everyone else who contributed.

Texts can now be created to fit within a shape or along a path, just by clicking the vector with the Text Tool. (MR!2432)

Text properties have been split into into Paragraph and Character tabs, making it clearer which level the properties are taking effect at. (MR!2470)

Carsten has also made sure the Text Tool works properly with touch input. (MR!2563)

But this journey's not over; if you use 5.3 pre-release builds, make sure to report bugs and leave feedback in the Text Tool Thread!

New Comic Panel Editing Tool

There's a new tool in the Toolbox: the Comic Panel Editing Tool. Agata designed this for creating comic panel gutters by cutting gaps in vector shapes. (MR!2331)

It can be set to cut different gap widths depending on whether the cut is horizontal, vertical, or diagonal past a certain angle. A second mode in Tool Options removes the gaps for easy re-adjustment.

Liquify Transform Speedup

The Transform Tool's Liquify mode has had some optimizations done by Agata. It's especially faster on large canvases, because it now avoids calculating outside the affected area. (MR!4261)

Before:

After:

Python Updated to 3.13

Krita's unstable builds have been updated from Python 3.10 to Python 3.13 (MR!2466). This has the potential to break plugins and scripts, so users of Krita Next should report any such issues to the developers of those plugins before 5.3.0's release.

If you're a plugin developer, check out the release notes for Python 3.11, Python 3.12, and Python 3.13 for information on the changes.

Community Report

Plans for 5.3.0's Upcoming Release

Krita's developers have put out a call for banner and icon artwork to promote the upcoming 5.3 release. This artwork must fit certain sizes and be licensed appropriately, so please read the rules before contributing!

November 2025 Monthly Art Challenge Results

17 forum members took on the challenge of the "Civilization Engulfed by Nature" theme. And the winner is… @Elixiah's two entries:

Time Keeper by @Elixiah

And Sunlit Silence

The December Art Challenge is Open Now

For this month's theme, winner @Elixiah has chosen Chiaroscuro, the strong contrast of light and dark, with runner-up @edgarej adding the optional challenge of a Christmas/holiday theme. Check out the topic for more details, and make some art that stands out like holiday lights on a dark night!

Featured Artwork

Best of Krita-Artists - October/November 2025

This month's Best of Krita-Artists Nominations thread received 17 nominations of forum members' artwork. When the poll closed, these five wonderful works made their way onto the Krita-Artists featured artwork banner:

Weird meeting by @Sad_Tea

Melon Soda city by @800000000W

Winter in the village by @Yarikart

Flower by @yuheng_zhang

Female head study by @netizenses

Best of Krita-Artists - November/December 2025

Take a look at the nominations for next month.

Ways to Help Krita

Krita is Free and Open Source Software developed by an international team of sponsored developers and volunteer contributors. That means anyone can help make Krita better!

Support Krita financially by making a one-time or monthly monetary donation. Or donate your time and Get Involved with testing, development, translation, documentation, and more. Last but not least, you can spread the word! Share your Krita artworks, resources, and tips with others, and show the world what Krita can do.

Other Notable Changes

Other notable changes in Krita's development builds from November 11, 2025 - December 14, 2025.

Stable branch (5.2.14):

• Canvas Input: Add a One Finger Hold gesture and set it by default to Sample Foreground Color From Merged Image. (Change, by Carsten Hartenfels)
• Color Sampler: The Color Sampler preview now defaults to a circle to be more visible when using touch input. The size of the circle can be adjusted under Settings->General->Cursor, or changed back to rectangles. (bug report) (Change, by Carsten Hartenfels)
• Layers Docker: Dragging-and-dropping a layer onto its own canvas now pastes a copy only if Ctrl is held, to prevent duplicating it by accident. Dropping a layer onto a different canvas still copy-pastes it as before, without holding Ctrl. (bug report Change, by Carsten Hartenfels)
• Filter Layers: Fix empty histogram when adding a new Levels, Threshold, Color Adjustment, or Cross-channel Filter Layer. (bug report) (Change, by Stuffins)
• Scripting: Fix Node.setChildNodes function to remove existing child nodes. (Change, by Stuffins)
• Android: Lessen the chance for saving corrupt files, by using a temporary file. (bug report Change, by Carsten Hartenfels)
• Android: Fix modifier keys getting stuck when inputting new custom shortcuts with a hardware keyboard. (bug report Change, by Carsten Hartenfels)
• macOS: Add support for QuickLook and Preview thumbnails for .kra, .krz, and .ora files on macOS Sequoia and later. (bug report (Change, by Ivan Yossi)
• macOS: Update app icon to support macOS Tahoe appearance settings. (Change, by Ivan Yossi)

Unstable branch (5.3.0-prealpha):

• Export: Don't show an error when cancelling an export. (bug report) Change, by Joshua Goins)

Nightly Builds

Pre-release versions of Krita are built every day for testing new changes.

Get the latest bugfixes in Stable "Krita Plus" (5.2.15-prealpha): Linux - Windows - macOS (unsigned) - Android arm64-v8a - Android arm32-v7a - Android x86_64

Or test out the latest Experimental features in "Krita Next" (5.3.0-prealpha). Feedback and bug reports are appreciated!: Linux - Windows - macOS - Android arm64-v8a - Android arm32-v7a - Android x86_64

This weekend, I attended the KDE PIM 2025 Sprint (AKA meeting) in Paris.

First, what does PIM mean? Personal information management.

Second, what does Personal information management mean? It's the software for managing email, calendar, address book, etc.

Third, this is going to be long, so let me thank https://haute-couture.enioka.com/en/ for hosting us (their office  is in Rue du Mail which seems very fitting for a meeting improving e-mail software) and thanks to KDE e.V. for sponsoring travel and hotel for the meeting. If you can, please donate so that more meetings like this can happen. 

This was my first time attending a PIM sprint even though I have been a KDE developer for a long time and a KMail/KOrganizer user for possibly even longer. 

It is true that these softwares are not in the most polished state, but honestly I would not know how to handle my email without KMail.

Anyhow here's a list of things I did: 

We talked a bit about bugs handling and it turns out not a lot of people are having a look at bugs, so I volunteered to watch the pim-bugs-null@kde.org address in Bugzilla (where most/all related bugs are assigned to) so I can help a bit. Note that I only committed to quickly read over them to try to make sure "really bad things" don't get overlooked. "Normal" bugs will always exist in every software and those will be fixed when they are fixed :)

If you also want to help you can set yourself to watch that pim-bugs-null@kde.org address in https://bugs.kde.org/userprefs.cgi?tab=email. 

On the topic of bugs, I managed to fix "left-click does not work on links with target="_blank" in HTML e-mails" with an impressive 1-liner change. It should be available with KDE Gear 25.12.1.

On Friday night, I experienced "sending emails does not work". After a few hours of debugging and thanks to our sysadmins, we found out it was due to "Your SMTP configuration was wrong". It seems older KMail versions were a bit more gracious when your configuration was wrong, but now it fails (fair enoug, although ideally it could give a better error). Incidentally I was not the only one with this problem since a few hours later we got this bug https://bugs.kde.org/show_bug.cgi?id=513284 that was basically the same. (My watching of pim-bugs-null@kde.org was already fruitful!)

On Saturday morning, I continued scratching my own itch and fixed a rather obscure bug where some context menu actions when right clicking on emails in KMail were not properly updated when expanding/collapsing threads.

KMime is undergoing API modernization and is slated to become a KDE Framework soon (TM). I helped a bit adapting code that uses KMime to the new API. 

On Sunday, I worked a bit on polishing address suggestion blacklisting on KMail (i.e. when I search for Foo, I don't want to get a suggestion to send an email to their old employer's email address). You can do that right now by right clicking on the "To" text field and selecting Completion Configuration and then going to the third tab. But that is a bit cumbersome (to the degree I had no idea that feature existed until the very same day). To make it a bit easier to discover, i have proposed adding a right click menu on the suggestions themselves that let's you blacklist that particular email address.

And now, a short list of things we did: (many more were done and will be explained in detail by other folks)

• Talk about switching the default backend to SQLite instead of mysql MariaDB. In general dropping servers (MariaDB/postgres) support would help making the code more maintainable. There are some people using it without problems, but Nico volunteered to do a test run during the sprint and he ended up with some problems, so there's still some things to debug there.
• Talk about doing a survey/adding more KUserFeedback data. We kind of agreed that first we need to know what question we really want to know the answer to and what would be the consequences of a given answer before spending time in designing a survey. But anyway if you use the KDE PIM software, please enable User Feedback in the settings, we promise we won't spy on you.
• New online accounts system. It should replace the not very useful accounts system that we now have (that also has a quite complicated dependency chain). It showed quite some promise in making things much more user friendly.

All in all it was a very productive meeting and I am happy to have attended.

On a closing note, one day we will have to speak about potentially sponsoring food for sprint attendees. We got travel and hotel sponsored, but I spent around 100 € on breakfast/lunch/dinner for that sprint (not going to any fancy place at all). Yes, I can spare that amount of money, but maybe some others in the community can not, and for sure we want them to also attend. One could even argue that having to spend money on top of spending a weekend and 2 work-holidays for the travel is a bit too much, it won't be me because I ❤️ KDE but someone could argue it 😁

KDE Gear 25.12 got just released.

This includes my fixes (or workarounds) for Konsole & Kate window activation on Wayland.

If you now start Kate or Konsole inside Konsole, the new processes will properly activate their windows to come on top of Konsole.

This works both for just starting new instances and for re-using already running ones.

For more details, see my older post about the implementation.

At the moment that only works for Konsole & Kate.

If that works nicely for our users, perhaps somebody will come up with a more generic way for that or we can move that workaround to some lower level of the stack.

:) For me that is already a nice Christmas present, I disliked that this was broken for years :)

Btw., thanks again for the amazing end of the year fundraiser results! €280k and counting :)

Feedback

You can provide feedback on the matching Reddit post.

Welcome to a new issue of This Week in Plasma!

This week the team made significant progress on KWin’s Wayland screen support. Specifically, better mirroring and custom modes — both items on the “Known Significant Issues” page — have been implemented for Plasma 6.6! The remaining items on that page are areas of active focus, too, as we race towards the Wayland finish line.

…But wait, there’s more!

Notable New Features

Plasma 6.6.0

The Window List widget lets you filter out windows not on the current screen, virtual desktop, or activity — just like the Task Manager widgets do. (Shubham Arora, plasma-desktop MR #3341)

Discover now lets you install and remove fonts on distros with package managers that use the PackageKit library. (Joey Riches, discover MR #1113)

Notable UI Improvements

Plasma 6.6.0

The “Minimize All” KWin script (which is included by default but not enabled) now also lets you minimize all windows besides the active one using the Meta+Shift+O keyboard shortcut. (Luis Bocanegra, bug #197952)

KWin now sets reasonable default scale factors for newly-connected TVs. (Xaver Hugl, kwin MR #8537)

Several related menu items in the context menus of the Kicker/Kickoff/Application Dashboard widgets have been grouped together. (Kisaragi Hiu, plasma-desktop MR #3381)

The kscreen-doctor tool now lets you know that it’s possible to mirror your screens. (Nicolas Fella, libkscreen MR #267)

Notable Bug Fixes

Plasma 6.5.4

Fixed a recent regression with desktop icons not staying on the right screen with some multi-screen arrangements. (Błażej Szczygieł, plasma-desktop MR #3330)

The Meta+P shortcut to open the screen chooser OSD now works on immutable-style distros. (Nate Graham, kscreen MR #440)

Plasma 6.5.5

Fixed a recent regression that caused screen freezes on some hardware right before power management kicked in. We’ve asked distros to backport the fix as ASAP as possible so everyone gets it as quickly. (Xaver Hugl, bug #513151)

Fixed a case where KWin could crash in the X11 session when using an older Valve Index headset. (David Edmundson, bug #507677)

Fixed an issue that could make stray modifier key events get sent to XWayland-using apps, especially when switching to them using keyboard shortcuts involving modifier keys. (Vlad Zahorodnii, link)

Fixed a case where KWin was handling drag-and-dropped text incorrectly, which could make drops fail in some apps. (Vlad Zahorodnii, bug #512235)

Fixed two screen locker issues that could make it slower to unlock via KDE Connect, and make it erroneously flash some text about a fingerprint or smart card reader when they’re not relevant. (Fushan Wen, kscreenlocker MR #296)

Fixed the back button in Folder View widgets’ list view display style. (Christoph Wolk, plasma-desktop MR #3387)

Fixed an issue in System Monitor that made it possible to end critical processes using the keyboard. (Oliver Schramm, bug #510464)

Other bug information of note:

• 5 very high priority Plasma bugs (same as last week). Current list of bugs
• 55 15-minute Plasma bugs (up from 37 last week). Current list of bugs

You might note a large increase in the number of HI priority bugs this week. This is because we’re beginning a quality initiative and using the HI priority level to track bugs to fix quickly. We want to make sure Plasma is getting extra large amounts of polish and stability work these days!

Other Notable Things in Performance & Technical

Plasma 6.5.4

Plugged a GPU memory leak in KDE’s portal implementation. (David Edmundson, bug #494138)

Plasma 6.5.5

Fixed a case where .desktop files with spec-violating names could cause massive amounts of log spam. (David Redondo, bug #512562)

Plasma 6.6.0

Massively improved support for screen mirroring in the Wayland session. Now it works really well! (Xaver Hugl, bug #481222 and kscreen MR #439)

You can now use the kscreen-doctor tool to add custom screen modes, useful for supporting exotic or misbehaving screens in the Wayland session. (Xaver Hugl, bug #456697)

Made the KWin rule to force a titlebar and frame also work for windows of native-Wayland apps. (Xaver Hugl, bug #452240)

You can now move windows with Meta+drag when using a drawing tablet stylus. (Vlad Zahorodnii, bug #509949)

How You Can Help

Donate to KDE’s 2025 fundraiser! It really makes a big difference. In total, KDE has raised over €280,000 during this fundraiser! The average donation is about €25. KDE truly is funded by you!

This money will help keep KDE strong and independent for years to come, and I’m just in awe of the generosity of the KDE community and userbase. Thank you all for helping KDE to grow and prosper!

If money is tight, you can help KDE by directly getting involved. Donating time is actually more impactful than donating money. Each contributor makes a huge difference in KDE — you are not a number or a cog in a machine! You don’t have to be a programmer, either; many other opportunities exist.

To get a new Plasma feature or a bugfix mentioned here, feel free to push a commit to the relevant merge request on invent.kde.org.

At this year’s Akademy (the yearly conference and gathering of KDE), there were several talks about immutable Linux distributions born inside KDE. The first, and more covered in the news was KDE Linux, the distro with an officially sounding name. And the second one was KDE Neon Core, which sounds like a continuation of KDE Neon, but is quite independent of it.

Things shouldn’t come in twos. There needs to be another immutable KDE distro, so I’m announcing the …

Now, this is a bit of a joke.

This is not really going to be a new distribution (for real, not like KDE Neon claimed not to be a distribution back in the day :) ). I don’t have the expertise nor the time to make a distribution from scratch.

But, while listening to the presentations about KDE Linux and KDE Neon Core, I had the idea to see how many of the planned features for those distributions I could implement based on an already existing and quite popular distribution called … if you have a keen eye, you might have guessed based on the image above … NixOS.

Step 1: Immutability

At the crux of it, immutability (along with other related buzzwords) means that you can not have an update break your system. There are no half-updates, no mixing incompatible versions of packages, etc. And if something gets broken with the new version, you can always roll back your system to a previous version.

This comes out of the box with NixOS. It just does it in a different way to other distributions. Its package manager allows installation of as many versions of a single package as needed, and the user or a running application “sees” only the versions they are compatible with.

When you update your system, the old packages are still installed, and you can reboot the computer into the pre-update state (previous versions are called generations).

Booting into an old state doesn’t really do anything special, it just makes you “see” the versions of the packages that were active in that version of your system. You don’t even need to reboot most of the time – if you see that a new version of LibreOffice doesn’t open your file correctly, and you want to try with the previous version, just ask Nix to launch the old version for you. The old version of LibreOffice is still on your system even if you’ve not booted into the system version (generation) it was installed on.

Steps 2..n

My main computer is (and always will be) Debian, but I’ve been using NixOS on my laptop for months now. And it works quite well.

As NixOS can be installed or replicated from a single configuration file, I plan to create a repository that will hold the definition of the system on my laptop (aka, the reference installation of KDE Ni! OS :) ) and to keep it updated while I go through each of the steps of simulating other distributions’ features.

This way, anyone who wants to have KDE Ni! OS on their computer will be able to install it by installing NixOS and using this file for system definition.

The next step will mainly be for developers – it will be about replacing a system package with a version you (or somebody else) developed. For example, if you want the Plasma Vault to behave a bit differently, or to test a fix for a bug you found, any sane distribution should allow you to do that easily, and without endangering the system integrity (no sudo make install). So, KDE Ni! OS will have to be able to do it as well.

I hate waiting for compilations. For day-to-day it may only be a minute or two, but once you start doing another task, the context switching distracts from what you were doing before and breaks everything up. Life is too short to be waiting for computers.

Obviously the first answer is to have a faster machine, but having a super fast laptop and a super fast PC all the time contributes to e-waste which I also hate. Some of my test devices for touch and tablet work are 5 year old Intel atom devices that I still sometimes need to compile on to fix things.

The solution is distributed compiling, using multiple computers to share the work.

Icecream or distcc used to be the tools back in the day, but they're both quite dated and have other issues.

There's a relatively new kid on the block, sccache. sccache primarily serves as a way of keeping your cached compiled assets around (think ccache), but also sharing them across users. Sharing cached assets requires exactly matching paths and dependencies and compilers so it's not that great for my needs; but it seems it would be perfect for flatpak and immutable cases.

But sccache also has another trick up it's sleeve; distributed compilation.

The documentation for sccache is a bit overwhelming packed with enterprise level features https://github.com/mozilla/sccache/blob/main/docs/Distributed.md.
It wasn't that clear how to do something simple, so I thought it might be useful to share how I got things working nicely for me.

Installation

Sccache is probably available in your distribution, note that not all distros include the shared compiler part.

If not you can download a version from https://github.com/mozilla/sccache/releases/download

The nice part is it's statically linked with no external dependencies so you can throw it on anything, even if it's immutable like KDE Linux or even a Steamdeck or two.

The parts

Scheduler

The scheduler is the key part of the operation; the client sends requests to the scheduler which in return replies with a list of schedulers that can recieve payloads distributing them accordingly.

Simple

Create a file as follows:

scheduler.conf

public_addr = "0.0.0.0:10600"
client_auth = { type = "token", token = "dave_is_great" }
server_auth = { type = "token", token = "dave_is_great" }

sccache-dist scheduler --config scheduler.conf

Docker

As I want the scheduler always on, I run it on a small home-server, where I prefer to docker-ise everything.

docker-compose:

version: '3.8'

services:
  sccache-scheduler:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        VERSION: "v0.10.0"
        SHASUM: bbf2e67d5e030967f31283236ea57f68892f0c7b56681ae7bfe80cd7f47e1acc
    image: sccache:latest
    container_name: sccache-scheduler
    ports:
      - "10600:10600"
    volumes:
      - ./scheduler.conf:/scheduler.conf:ro
    entrypoint: ["/usr/local/bin/sccache-dist", "scheduler", "--config", "/scheduler.conf"]
    restart: unless-stopped
    environment:
      - SCCACHE_NO_DAEMON=1

Dockerfile

FROM alpine:3.9.2

ARG VERSION
ARG SHASUM

RUN apk add clang
RUN apk add curl
RUN apk add --no-cache bubblewrap

RUN curl -L https://github.com/mozilla/sccache/releases/download/$VERSION/sccache-dist-$VERSION-x86_64-unknown-linux-musl.tar.gz > sccache-dist.tar.gz \
    && tar xf sccache-dist.tar.gz \
    && mv sccache-dist-$VERSION-x86_64-unknown-linux-musl/sccache-dist /usr/local/bin/sccache-dist \
    && rm -r sccache-dist.tar.gz sccache-dist-$VERSION-x86_64-unknown-linux-musl

RUN apk del curl

ENTRYPOINT ["/usr/local/bin/sccache"]

and the scheduler.conf as above.

Servers (build machines)

This is the part that does the building.
The config takes the address of the scheduler, but also the server's own IP address as a sort of "callback" address.

It needs to run as root in order to have capabilities to set up sandboxing and restrict it back down to something lower than where we started. The sitaution is a bit silly, but it is what it is.

server.conf

public_addr = "192.168.1.YOURIPADDRESS:10501"
scheduler_url = "http://192.168.1.SCHEDULERIPADDRESS:10600"
cache_dir = "/tmp/toolchains"
scheduler_auth = { type = "DANGEROUSLY_INSECURE" }

[builder]
type = "overlay"
# The directory under which a sandboxed filesystem will be created for builds.
build_dir = "/tmp/build"
# The path to the bubblewrap version 0.3.0+ `bwrap` binary.
bwrap_path = "/usr/bin/bwrap"

Then you can run sudo sccache-dist server --config server.conf

Systemd

As I want this running constantly on my desktop and laptop I use a systemd service.

/etc/systemd/system/sccache.service
[Unit]
Description=sccache scheduler
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
ExecStart=/usr/bin/sccache-dist server --config /etc/sccache/server.conf
Restart=on-failure
RestartSec=5s

[Install]
WantedBy=multi-user.target

Clients

The final part is relatively simple, making local builds use the other build servers.

First we need to set up a config as follows:

.config/sccache/config

[dist]
scheduler_url = "http://192.168.1.SCHEDULERIPADDRESS:10600"
toolchains = []
toolchain_cache_size = 5368709120
auth = { type = "token", token = "dave_is_great" }

Cmake

Enabling requires just telling cmake to use the relevant wrapper with -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache

kde-builder

And/or it to your kde-builder as follows:

.config/kde-builder.yaml

global:
  cmake-options: -GNinja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_EXPORT_COMPILE_COMMANDS=ON  -DCMAKE_CXX_COMPILER=clang++ \
    -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache 

and reconfigure the project(s)

Quirks and workarounds

The most annoying quirk is servers need a consistent IP address within your network. Servers register to the scheduler with a fixed IP address. When clients queue jobs they are given the IP addresses back from the scheduler and are expected to then talk to the build server(s) directly. Using hostnames doesn't work.

Note also if you change your local .config/sccache you may need to run sccache --stop-server on the client to relaunch. Confusingly in this case 'server' refers to a process on the client that compile jobs are thrown at.

Debugging

sccache --dist-status will show the connected schedulers and how many total active jobs

Managing job count

By default ninja schedules the same number of jobs as you have local cores for. It's unaware of the many other cores you have.
I have this in my zshrc to set the number of jobs to the total number on the scheduler at that time.

function getSccacheCPUs() {
        sccache --dist-status  | jq '."SchedulerStatus"[1].num_cpus'
}
alias ks='MAKEFLAGS=-j${getSccacheCPUs} kde-builder'

Comparison to icecream

Cons:

• The setup process is a lot more laborious than icecream's magic turn-up-and-compile structure
• No cool UI to see how many tasks are being compiled.

Pros:

• It's very robust to network issues. If the scheduler is down or no servers are available things build locally extremely transparently
• It also has it's own equivalent of a local 'ccache' which means you don't need to worry about daisy-chaing compilers wrappers to still have cached output.
• It's actively maintained, the last meaningful commit in icecream is years ago