Very excited to be founding @amutable.com with @pid1.bsky.social and @cbrauner.bsky.social. We are joined by one of the strongest Linux teams I could imagine building important foundational technologies that enable whole new capabilities built on trust and integrity.

Ringing in 2026, I'm thrilled to join @amutable.com with @cbrauner.bsky.social, @chrskhl.net, and @pid1.bsky.social — alongside a wildly talented founding engineering team — to redefine what we expect for infrastructure integrity, declarative systems, compliance, and trust.

Today I'm super excited to announce Amutable, our new company together with @pid1.bsky.social and @chrskhl.net . We have an amazing founding team. I'm very happy they are on board for the ride. I can't wait to show everyone what we're building. Made with ❤️ in Berlin. amutable.com/blog/introdu...

Today we announce Amutable and our mission to deliver determinism and verifiable integrity to Linux systems. Amutable is founded in Berlin by @chrskhl.net , @cbrauner.bsky.social and @pid1.bsky.social. Read the announcement: amutable.com/blog/introdu...

A reminder that the All Systems Go! 2025 CFP closes on June 13th. Submit your talk about foundational user-space Linux technologies before the deadline to be considered. 👉 cfp.all-systems-go.io/all-systems-...

I feel like #Android would be a prime candidate to rely on SO_PEERPIDFD in their bluetooth stack. And if they don't, they probably should.

6/n And even if the current crashing thread isn't the actual thread-group leader we know that the thread-group leader cannot be reaped until all of its subthreads have exited.

5/n We're installing a pidfd for the thread-group leader even if a subthread is calling do_coredump(). We know that task linkage hasn't been removed yet.

4/n Since usermode helpers are either children of the system_unbound_wq workqueue or kthreadd we know that the file descriptor table is empty and can thus always use three as the file descriptor number.

3/n When the usermode helper process is forked we install a pidfd file descriptor three into the usermode helper's file descriptor table so it's available to the exec'd program.

2/n There are tricky race-windows that cannot be easily closed by userspace. There's various ways like looking at the start time of a process to make sure that the usermode helper process is started after the crashing process but it's all very very brittle and fraught with peril.

1/n Oh yeah, I already mentioned this a while ago but I also added support for pidfds in Linux coredumps. /proc/sys/kernel/core_pattern has been extended so userspace can instruct the kernel to install a pidfd for the crashing process into the usermode helper process, e.g., systemd-coredump.

So a while ago we did pidfds for AF_UNIX sockets. Alexandr Mikahlitsyn did all of the heavy lifting. Specifically we added SO_PEERPIDFD and SCM_PIDFD. They are analogues to SCM_PEERCRED and SCM_CREDENTIALS.

Picked back up the work for VFS {g,u}id squashing. IOW, mapping all {g,u}ids down to a single {g,u}id. web.git.kernel.org/pub/scm/linu...

util-linux has merged support for statmount() and listmount() to list mounts: github.com/util-linux/u... This should be a nice performance improvement. See brauner.io/2024/12/16/l... for some details on listmount() and statmount(). #linux #kernel

I'm organizing the #containers and #kernel devrooms at FOSDEM 2025 with the usual suspects. containers: fosdem.org/2025/schedul... kernel: fosdem.org/2025/schedul... See you in Brussels!

I've written a post that shows how to list all mounts in all mount namespaces (all mounts on the system) using new apis we added to the #vfs last year. brauner.io/2024/12/16/l... #kernel #linux #vfs