1745908 - `_Py_HashRandomization_Init` Python error at the end of every mach invocation

Status: RESOLVED FIXED

(Firefox Build System :: General, defect, P1)

Description

[Dave Townsend [:mossop]]

On Windows every time I do a build or package or something the command appears to work but the last line logged is this:

Fatal Python error: _Py_HashRandomization_Init: failed to get random numbers to initialize Python

Comment 1

[Bryce Seager van Dyk [:bryce] (he/him) - Not reading bugmail]

Also hitting this. I didn't realize it was non fatal until finding this bug. Seeing Fatal Python error after mach commands had me assuming stuff was busted.

On top of looking scary, it can also make prompts confusing when running commands that require interaction:

Paste API Token from that page: Fatal Python error: _Py_HashRandomization_Init: failed to get random numbers to initialize Python

though this also seems to have worked okay with if I ignore the error and just respond to the prompt.

Comment 2

[Mitchell Hentges [:mhentges] 🦀]

I'm going to tentatively mark this as "regressed by" the glean update, because one-off error messages at the end of Mach processes (even those as simple as, say, ./mach python -c pass) are generally associated with Glean behaviour in a background thread.

If that indeed wasn't the cause, I'll be able to investigate more closely tomorrow.

Comment 3

[Jan-Erik Rediger [:janerik] (Away 2026-04-02 - 2026-04-10)]

After a quick web search I think I know what's going on:
We recently landed a Glean patch to set PYTHONPATH in the launched subprocess, but they way we're doing it overrides all other environment variables.
It seems for the RNG to work it needs SYSTEMROOT to be set. That's something I can fix in Glean.

Comment 4

[Jan-Erik Rediger [:janerik] (Away 2026-04-02 - 2026-04-10)]

Verified a fix, gonna send that soon.

Comment 5

[GitHub Bugzilla PR Linker]

Attachment: Link to GitHub pull-request: https://github.com/mozilla/glean/pull/1908

Comment 6

[Jan-Erik Rediger [:janerik] (Away 2026-04-02 - 2026-04-10)]

Attachment: Bug 1745908 - Update Glean in mach to prevent RNG bug. r?dexter

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5aadefcc52b5
Update Glean in mach to prevent RNG bug. r=Dexter

Comment 8

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1744674

Comment 9

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/5aadefcc52b5