From d60a9ceefcfb40aaa2db0299c561af301e82b86a Mon Sep 17 00:00:00 2001 From: Om Pathak Date: Tue, 23 Jun 2026 00:00:53 -0400 Subject: [PATCH] docs: note WSL filesystem caveat for MultiProcessCollector Signed-off-by: Om Pathak --- docs/content/multiprocess/_index.md | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/docs/content/multiprocess/_index.md b/docs/content/multiprocess/_index.md index f7befef8..cd129930 100644 --- a/docs/content/multiprocess/_index.md +++ b/docs/content/multiprocess/_index.md @@ -35,6 +35,12 @@ between process/Gunicorn runs (before startup is recommended). This environment variable should be set from a start-up shell script, and not directly from Python (otherwise it may not propagate to child processes). +Note: on Windows Subsystem for Linux (WSL), set `PROMETHEUS_MULTIPROC_DIR` to a +Linux-native filesystem path (e.g. `/tmp` or `/home/`) rather than a +Windows-mounted path (e.g. `/mnt/c/...`). On Windows-mounted filesystems the +per-process metric files can be written with an incorrect internal offset, +causing the collector to silently read no data. + **2. Metrics collector**: The application must initialize a new `CollectorRegistry`, and store the