{"record":{"id":"8080933b9e59a141","repo":"facebook/flow","slug":"failed-to-spawn-server-daemon","errorCode":null,"errorMessage":"failed to spawn server daemon: {}","messagePattern":"failed to spawn server daemon: (.+?)","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"rust_port/crates/flow_server_monitor/src/flow_server_monitor_server.rs","lineNumber":698,"sourceCode":"                .unwrap_or_default()\n                .as_nanos()\n                & 0xFFFFFFFFFFFFFFFFu128\n        );\n        let server_options_arc = std::sync::Arc::new(_server_options.clone());\n\n        let server_handle = flow_server::server::daemonize(\n            &init_id,\n            _log_file,\n            _argv,\n            lazy_mode.clone(),\n            *no_flowlib,\n            *ignore_version,\n            file_watcher_pid.map(|p| p as u32),\n            start_cause,\n            server_options_arc,\n            &monitor_options.cli_overrides,\n        )\n        .unwrap_or_else(|e| panic!(\"failed to spawn server daemon: {}\", e));\n        let pid: i32 = server_handle.child.id() as i32;\n        // Cross-platform: `TcpStream::try_clone` duplicates the socket on\n        // both Unix and Windows. The previous code used\n        // `nix::unistd::dup(BorrowedFd)`, which is Unix-only.\n        let in_stream = flow_daemon::descr_of_in_channel(&server_handle.channels.0)\n            .try_clone()\n            .expect(\"failed to dup server->monitor channel\");\n        let out_stream = flow_daemon::descr_of_out_channel(&server_handle.channels.1)\n            .try_clone()\n            .expect(\"failed to dup monitor->server channel\");\n        let daemon_handle = Arc::new(Mutex::new(Some(server_handle)));\n        let close_daemon_handle = daemon_handle.clone();\n        let close = move || {\n            let mut guard = match close_daemon_handle.lock() {\n                Ok(guard) => guard,\n                Err(poisoned) => poisoned.into_inner(),\n            };\n            if let Some(handle) = guard.as_mut() {","sourceCodeStart":680,"sourceCodeEnd":716,"githubUrl":"https://github.com/facebook/flow/blob/f88ac94bcf6992f5d5a158854d94613ebb92c6e6/rust_port/crates/flow_server_monitor/src/flow_server_monitor_server.rs#L680-L716","documentation":"When the flow-server-monitor needs a server, it calls flow_server::server::daemonize() to spawn the Flow server daemon. Any Err from daemonize is panicked on with 'failed to spawn server daemon: {}'. daemonize fails most commonly on its lock check — 'There is already a server running for <root>' — but the same path carries log-open and temp-dir failures, so read the formatted error text for the true cause.","triggerScenarios":"Starting a monitor while another server already holds the lock for the same root+flowconfig combination; temp dir or log file setup failing inside daemonize (the log-file open error propagates here); the registered entry-point binary missing or not executable.","commonSituations":"Two IDEs/tools starting Flow on the same project concurrently; a previous daemon that was never stopped; switching flowconfig_name while the old server still runs; permission changes in the temp dir after the daemon user changed.","solutions":["Stop the existing server for that root first (flow stop, or remove the lock file under the flow temp dir) and retry the monitor start.","Read the text after the colon — it is daemonize's own message and names the actual failure ('already a server running', log open failure, missing entry point).","Fix temp-dir/log permissions if that is the reported cause.","If it fails on every start, wipe the stale lock and log files under <temp_dir>/flow for that root."],"exampleFix":"# before: second server start on the same root\nflow monitor-start ...  # panic: failed to spawn server daemon: Error: There is already a server running for /repo\n\n# after\nflow stop && flow monitor-start ...","handlingStrategy":"retry","validationCode":"# before starting the monitor, ensure no server holds the lock for this root\nflow status --root \"$ROOT\" >/dev/null 2>&1 && flow stop --root \"$ROOT\"\nrm -f \"$TMPDIR/flow/$(root_hash \"$ROOT\")/lock\" 2>/dev/null || true","typeGuard":null,"tryCatchPattern":"# pseudo-code for a supervisor\nfor attempt in 1 2; do\n  flow monitor-start ... && break\n  # panic text names the cause: 'already a server running' -> recycle\n  flow stop 2>/dev/null || rm -f \"$FLOW_TMP/lock\"\n  sleep 1\ndone","preventionTips":["Sequence starts: stop-then-start in scripts; never start two monitors on one root.","When switching flowconfig_name for a root, stop the existing server first.","Run the monitor as the user that owns the temp dir and lock files.","Clean lock files during host provisioning/logout so next start cannot collide."],"tags":["server","daemon","lock","process-spawn","startup","monitor"],"backgroundTag":"process-spawn-failed","analyzedSha":"f88ac94bcf6992f5d5a158854d94613ebb92c6e6","analyzedAt":"2026-08-20T10:41:37.992Z","schemaVersion":2},"datasetVersion":"2026-08-23T08:06:27.607Z"}