Porting systemd to musl Libc-powered Linux

Original Article ↗ Hacker News Discussion ↗

Porting systemd to musl & upstreaming

  • Multiple PRs to support musl have already been merged; likelihood of full upstreaming is described as high.
  • Many patches fix assumptions where glibc exposes extra symbols or APIs and musl does not.
  • Prior debates show musl maintainers dislike copying non‑POSIX “glibc‑isms”, while systemd maintainers don’t want to re‑implement glibc extensions they rely on.
  • Some suggest a compatibility libc or headers to provide glibc APIs on top of musl; existing gcompat is noted as binary‑only, not for compiling.
  • One controversial API is malloc_info (XML dump of allocator state) used only for debugging; critics call it a bad interface and resent that making it optional “can’t be upstreamed.”

Boot performance & init systems

  • Blog claims systemd boots in ~1/3 the time of OpenRC; some find this suspiciously large but note OpenRC’s parallel startup is disabled by default and documented as unstable.
  • Several argue boot time doesn’t matter for always‑on servers/laptops, but others stress its importance for embedded, serverless, microVMs, and post‑S3 laptops.
  • Some report OpenRC (or even a minimal inittab) already boots “fast enough”; others say OpenRC is “known slow” and that systemd wins on parallelization.

Systemd benefits vs drawbacks

  • Pro‑systemd points:
    • Huge ecosystem support, wide testing, and heavy sponsorship.
    • Big win for distro maintainers vs duct‑taped sysvinit.
    • Rich features: socket activation, user services, declarative sandboxing (namespaces, syscall filtering), tmpfiles, TPM secrets, logind, networkd.
  • Critiques:
    • “Good ideas, bad implementation” and poor UX (confusing defaults, unhelpful error messages, sparse docs).
    • journald seen by some as slow, resource‑heavy, single‑bucket logging with awkward defaults and binary format; others report it performing fine even on weak hardware.
    • Past high‑impact bugs are cited (system‑bricking issues, efivarfs RW, DHCP failures, coupling into OpenSSH).
    • Some view systemd as work‑only “big contraption,” preferring simpler stacks at home.

Alpine, OpenRC, and ecosystem tensions

  • Alpine’s musl/busybox/OpenRC stack is praised for minimalism, good battery life, and low background activity.
  • Strong resistance to systemd entering Alpine or its ecosystem; fear of packages eventually requiring systemd.
  • Counter‑argument: distros voluntarily chose systemd because alternatives are slower, less featureful, and harder to integrate; forking to avoid systemd is possible but costly, so “choice” feels constrained.

musl vs glibc performance & tradeoffs

  • Shared links show mostly small performance differences, with one outlier reporting musl much slower for multithreaded allocation.
  • Some believe musl’s malloc and overall performance are weaker; others note glibc’s allocator is hardly ideal either.
  • General view: musl prioritizes size and simplicity, glibc prioritizes features and speed; you usually trade one for the other.