openclaw/docs/gateway/gateway-lock.md

summary, read_when, title

summary	read_when	title
Gateway singleton guard: file lock plus WebSocket/HTTP bind	Running or debugging the gateway process Investigating single-instance enforcement	Gateway lock

Why

• Only one gateway process should own a state directory; run additional gateways with isolated profiles, state directories, configs, and ports.
• Survive crashes/SIGKILL without leaving stale lock files behind.
• Fail fast with a clear error when another gateway already owns the port.

Three layers

Startup enforces ownership in three steps, in order:

1. State ownership lock acquires a lock keyed by the canonical state directory. Every Gateway participates, including Gateways started with OPENCLAW_ALLOW_MULTI_GATEWAY=1, so destructive SQLite maintenance cannot race a live owner.
2. Config lock acquires the historical per-config lock and records the runtime port. Multi-Gateway mode skips this config singleton but retains the state ownership lock.
3. Socket bind binds the HTTP/WebSocket listener (default ws://127.0.0.1:18789) as an exclusive TCP listener.

Each layer can fail independently and throws its own GatewayLockError.

State and config locks

• Lock liveness comes from the recorded PID, platform process start identity when available, and Gateway process identity. A verified owner remains authoritative during startup before its port begins listening.

• A dedicated SQLite coordinator serializes metadata inspection, stale-owner reclamation, and lock replacement. Its exclusive transaction is released automatically if the owning process crashes.

• If a lock file is missing or the recorded owner process is gone, startup reclaims the lock and continues.

• If either lock is actively held, startup retries for up to 5 seconds (default) before giving up:

  GatewayLockError("gateway already running (pid <pid>); lock timeout after <ms>ms")
  

Socket bind

• 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.

• If the port is still in use after retries:

  GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>")
  

• Other bind failures:

  GatewayLockError("failed to bind gateway socket on ws://127.0.0.1:<port>: <cause>")
  

On shutdown, the gateway closes the HTTP/WebSocket server and removes its state and config lock files.

Operational notes

• 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>.
• OPENCLAW_ALLOW_MULTI_GATEWAY=1 permits multiple config/runtime instances, not shared mutable state. Each instance still needs a unique OPENCLAW_STATE_DIR.
• 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.
• 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.

Related

• Multiple Gateways - running multiple instances with unique ports
• Troubleshooting - diagnosing EADDRINUSE and port conflicts