NixOS: native recursive FS watcher never loads (libstdc++.so.6 not found) #53210

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1. github-actions

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   neriousy

   on Oct 4, 2026
2. github-actions commented on Oct 4, 2026

   

   github-actionsBot

   on Oct 4, 2026 – with GitHub Actions

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   This issue appears to overlap with existing reports. Please check:

   • #18447: Nix package missing the libstdc++.so.6 runtime dependency.
   • #28964: NixOS report with the same failed to load watcher binding / libstdc++.so.6 error.
3. luochen1990 commented on Oct 27, 2026

   

   luochen1990

   on Oct 27, 2026

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   Adding production evidence from a long-running NixOS deployment (2.0.26, 0d61729b3f, Nix-packaged, opencode serve --service):

   • The daemon log shows watcher backend not supported 1333 times over a ~21-hour window (~1/min — it retries on every watch attempt). Verbatim except elided run/span ids and the project path:

     timestamp=2026-10-26T23:31:37.637Z level=ERROR run=... message="watcher backend not supported" directory=/home/lc/ws/<project>/.opencode platform=linux http.span=... role=server
     

   • Behavioral impact beyond skills: directory-level changes — new/removed/swapped plugin entries, and config files (which, as observed, aren't covered by a working per-file watch either) — never hot-reload. Per-file watches on already-loaded plugin entries still fire (that's how the rescan in the issue we filed separately (Plugins are silently unloaded after a plugin-dir symlink swap is followed by any rescan — NixOS home-manager deployments #59725) gets triggered). The only thing that eventually picks up directory-level changes is the supervisor's periodic full rescan (~24h), so a long-running service silently runs with stale config/plugins for up to a day.

   • One timing note connecting to that separate issue (Plugins are silently unloaded after a plugin-dir symlink swap is followed by any rescan — NixOS home-manager deployments #59725): because the directory watcher is dead, a plugin-dir symlink swap is not picked up immediately — the unload we describe there is delayed until the ~24h fallback rescan. The dead watcher changes the timing and visibility of that bug (delayed, mysterious, logs silent); the unload itself is its own defect.

   We now run a systemd path unit + idle gate that restarts the service on plugin-dir changes as a workaround, but a proper fix at the packaging layer (e.g. the stdenv.cc.cc.lib wrapper approach proposed in #18447 (linked upthread), or a static/bundled addon) would remove the whole class.
4. opencodejr commented on Oct 27, 2026

   

   opencodejrBot

   on Oct 27, 2026

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   Thanks for the detailed report and the fix PR. I could reproduce this, but not on NixOS itself: I hid the system libstdc++.so.6 on a regular Linux x64 machine to imitate it.

   What I found on 2.0.22:

   • The bundled @parcel/watcher addon needs libstdc++.so.6 and has no RUNPATH. The opencode binary itself doesn't need it.
   • With libstdc++ available, the ~/.config/opencode directory watch starts with backend=inotify.
   • With it hidden, the same watch logs watcher backend not supported ... platform=linux. The type=entries watches still start with backend=node.
   • With libstdc++ hidden but its directory on LD_LIBRARY_PATH (the approach in fix(nix): expose libstdc++ so the native fs watcher loads on NixOS #53213), the directory watch starts normally again.

   It still happens on the latest dev (fd8268e) run from source: with libstdc++ hidden, both ~/.config/opencode and ~/.config/opencode/skills log watcher backend not supported. nix/opencode.nix there still only puts wayland on LD_LIBRARY_PATH, and the devshell adds no libstdc++.

   I only checked the error in the logs, not that an edited skill fails to reload. The script below runs these checks; it needs root because it temporarily moves the system libstdc++ and puts it back on exit.

   Related: #18447 and #28964 (same missing libstdc++, closed as stale), #56255 (config edits not picked up on the Nix build, closed as a duplicate of this one) and #53213 (your fix).

   Reproduction script (repro.sh)

   #!/usr/bin/env bash
   # Reproduces #53210: the bundled @parcel/watcher native addon needs libstdc++.so.6
   # (dynamic NEEDED, no RUNPATH). When the loader can't resolve it — as on NixOS,
   # which has no global /lib with libstdc++ and whose Nix wrapper only adds wayland
   # to LD_LIBRARY_PATH — recursive directory watches fail with
   # "watcher backend not supported" and skill/config edits are never picked up.
   #
   # NixOS is simulated by hiding the system libstdc++ (needs root; restored on exit).
   # Usage: repro.sh [opencode command...]   (default: opencode)
   set -u
   OC=("${@:-opencode}")
   LIBDIR=/lib/x86_64-linux-gnu
   HIDE=/tmp/opencode/hidden-libstdc
   run() {
     local label=$1; shift
     local H; H=$(mktemp -d /tmp/opencode/home.XXXX)
     mkdir -p "$H/.config/opencode/skills/demo" "$H/proj"
     printf -- '---\nname: demo\ndescription: demo skill\n---\nv1\n' > "$H/.config/opencode/skills/demo/SKILL.md"
     (cd "$H/proj" && env HOME=$H XDG_CONFIG_HOME=$H/.config XDG_DATA_HOME=$H/.local/share \
       XDG_STATE_HOME=$H/.local/state XDG_CACHE_HOME=$H/.cache "$@" \
       timeout 30 "${OC[@]}" api --standalone --print-logs --log-level debug get /api/skill > "$H/log" 2>&1)
     echo "===== $label ====="
     grep -iE "type=directory|not supported|libstdc|binding" "$H/log" | grep -v stopped | sed 's/^.*message=/  message=/' | head -20
   }
   run "libstdc++ available (normal distro)"
   mkdir -p "$HIDE"
   mv $LIBDIR/libstdc++.so.6* "$HIDE"/ && ldconfig
   trap 'mv "$HIDE"/libstdc++.so.6* $LIBDIR/ && ldconfig' EXIT
   run "libstdc++ NOT resolvable (as on NixOS)"
   run "libstdc++ hidden, but its dir on LD_LIBRARY_PATH (proposed Nix wrapper fix)" LD_LIBRARY_PATH=$HIDE

   Run it: bash repro.sh

   👍React with 👍1Reacted by Benoit de Chezelles
5. opencodejr

   added

   reproduced

   on Oct 27, 2026