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Source-grounded rewrite of 529 published docs pages with per-unit information-loss verification: 1,713 factual corrections cited to src/**, generated surfaces regenerated, frontmatter titles preserved for i18n, release notes pages untouched. All docs gates green. Closes #100141
60 lines
2.9 KiB
Markdown
60 lines
2.9 KiB
Markdown
---
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summary: "Gateway singleton guard: file lock plus WebSocket/HTTP bind"
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read_when:
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- Running or debugging the gateway process
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- Investigating single-instance enforcement
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title: "Gateway lock"
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---
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## Why
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- Only one gateway process should own a given config + port on a host; run additional gateways with isolated profiles and unique ports.
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- Survive crashes/SIGKILL without leaving stale lock files behind.
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- Fail fast with a clear error when another gateway already owns the port.
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## Two layers
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Startup enforces single-instance ownership in two independent steps, in order:
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1. **File lock** acquires a per-config lock file under the state lock directory. As part of acquiring it, startup probes the configured port for a live listener to detect a stale (crashed) lock owner.
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2. **Socket bind** binds the HTTP/WebSocket listener (default `ws://127.0.0.1:18789`) as an exclusive TCP listener.
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Each layer can fail independently and throws its own `GatewayLockError`.
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### File lock
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- If the lock file is missing, the recorded owner process is gone, or the owner's port probe shows no live listener, startup reclaims the lock and continues.
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- If the lock is actively held and none of the above apply, startup retries for up to 5 seconds (default) before giving up:
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```text
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GatewayLockError("gateway already running (pid <pid>); lock timeout after <ms>ms")
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```
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### Socket bind
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- On `EADDRINUSE`, startup retries the bind for up to 20 attempts at 500ms intervals (roughly 10 seconds total) to ride out a `TIME_WAIT` window after a recently exited process.
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- If the port is still in use after retries:
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```text
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GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>")
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```
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- Other bind failures:
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```text
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GatewayLockError("failed to bind gateway socket on ws://127.0.0.1:<port>: <cause>")
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```
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On shutdown, the gateway closes the HTTP/WebSocket server and removes the lock file.
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## Operational notes
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- If the port is occupied by a different, non-gateway process, the error is the same; free the port or choose another with `openclaw gateway --port <port>`.
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- Under a service supervisor, a new gateway process that hits either error above first probes `/healthz` on the existing process. If that process is healthy, the new process leaves it in control instead of failing. On systemd, it exits with code `78`; the unit's `RestartPreventExitStatus=78` stops `Restart=always` from looping on a lock or `EADDRINUSE` conflict. If the existing process never becomes healthy, the health-probe retry is time-bounded and startup then fails with the lock error above instead of looping forever.
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- The macOS app keeps its own lightweight PID guard before spawning the gateway; the file lock and socket bind above are the actual runtime enforcement.
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## Related
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- [Multiple Gateways](/gateway/multiple-gateways) - running multiple instances with unique ports
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- [Troubleshooting](/gateway/troubleshooting) - diagnosing `EADDRINUSE` and port conflicts
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