{"record":{"id":"f6007bca391f25c3","repo":"hashicorp/nomad","slug":"error-opening-writer-at-s-w","errorCode":null,"errorMessage":"error opening writer at %s: %w","messagePattern":"error opening writer at (.+?): %w","errorType":"error_code","errorClass":null,"httpStatus":null,"severity":"error","filePath":"client/lib/fifo/fifo_unix.go","lineNumber":64,"sourceCode":"\t}\n\treturn f, nil\n}\n\n// OpenWriter opens a fifo file for writer, assuming it already exists, returns io.WriteCloser\nfunc OpenWriter(path string) (io.WriteCloser, error) {\n\tdir := filepath.Dir(path)\n\tbase := filepath.Base(path)\n\n\troot, err := os.OpenRoot(dir)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"error opening fifo parent directory %q: %w\", dir, err)\n\t}\n\tdefer root.Close()\n\n\t// also uses O_NOFOLLOW under the hood\n\tf, err := root.OpenFile(base, os.O_WRONLY, 0)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"error opening writer at %s: %w\", path, err)\n\t}\n\treturn f, nil\n}\n\n// Remove a fifo that already exists at a given path\nfunc Remove(path string) error {\n\tdir := filepath.Dir(path)\n\tbase := filepath.Base(path)\n\n\troot, err := os.OpenRoot(dir)\n\tif err != nil {\n\t\treturn fmt.Errorf(\"error opening root dir %q: %w\", dir, err)\n\t}\n\tdefer root.Close()\n\n\treturn root.Remove(base)\n}\n","sourceCodeStart":46,"sourceCodeEnd":82,"githubUrl":"https://github.com/hashicorp/nomad/blob/482b49bf1aec006f089bcfc7e632d8f6ac303e5e/client/lib/fifo/fifo_unix.go#L46-L82","documentation":"OpenWriter opens the FIFO itself for writing after successfully opening the parent directory via os.Root. This error wraps a failure of root.OpenFile(base, os.O_WRONLY) — the file exists check fails (ENOENT), permissions deny write (EACCES), or the O_NOFOLLOW-protected open rejects a symlink. Opening a FIFO for write also fails with ENXIO if no reader is listening.","triggerScenarios":"Calling fifo.OpenWriter(path) when the FIFO was not created (ENOENT), the process lacks write permission (EACCES), the target is a symlink (O_NOFOLLOW rejection), or no reader has the FIFO open (ENXIO).","commonSituations":"Writer started before the log-monitor created the FIFO; FIFO removed by cleanup between creation and open; path replaced by symlink after a previous insecure setup; ENXIO when the reader process died.","solutions":["Ensure the FIFO exists first: call fifo.Create(path, mode) or start the reader before the writer","On ENXIO, verify a reader (OpenReader/CreateAndRead) is open on the FIFO before writing","Remove and recreate stale or symlinked FIFOs with fifo.Remove + fifo.Create","Check write permissions on the FIFO for the writing user"],"exampleFix":"// before\nw, err := fifo.OpenWriter(\"/run/containerd/io/stdout\")\n// after\nif err := fifo.Create(\"/run/containerd/io/stdout\", 0o600); err != nil && !errors.Is(err, os.ErrExist) { return err }\nw, err := fifo.OpenWriter(\"/run/containerd/io/stdout\")","handlingStrategy":"retry","validationCode":"fi, err := os.Lstat(path)\nif err != nil || fi.Mode()&os.ModeNamedPipe == 0 {\n\treturn fmt.Errorf(\"fifo %s not present\", path)\n}","typeGuard":"func isENXIO(err error) bool {\n\treturn errors.Is(err, syscall.ENXIO)\n}","tryCatchPattern":"w, err := fifo.OpenWriter(path)\nif err != nil {\n\tswitch {\n\tcase errors.Is(err, fs.ErrNotExist):\n\t\t// create fifo then retry open\n\tcase errors.Is(err, syscall.ENXIO):\n\t\t// no reader attached; wait for reader and retry\n\t}\n\treturn err\n}","preventionTips":["Start the reader before opening the writer, or handle ENXIO with retry","Never symlink the fifo path; O_NOFOLLOW will reject it","Create the FIFO idempotently and tolerate os.ErrExist","Verify write permissions on the fifo for the writer user"],"tags":["go","filesystem","fifo","file-not-found"],"backgroundTag":"fifo-open-failed","analyzedSha":"482b49bf1aec006f089bcfc7e632d8f6ac303e5e","analyzedAt":"2026-09-04T07:54:14.808Z","contentChangedAt":"2026-09-04T07:54:14.808Z","schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}