denoland/deno · error · SystemError

ERR_FS_CP_SOCKET

ERR_FS_CP_SOCKET

Error message

Cannot copy a socket file

What it means

During copy dispatch, if the source stat reports a socket, fs.cp rejects with CpError::Socket (kind 'SOCKET'), mapped by throwCpError to ERR_FS_CP_SOCKET ('Cannot copy a socket file', errno EINVAL). Unix domain sockets hold no persistent content — they are a rendezvous endpoint — so copying their directory entry is meaningless and refused.

Solutions

1. Exclude socket entries: filter with fs.lstat + stats.isSocket() (or use glob exclude) before copying
2. Clean the source tree of runtime sockets before archiving (sockets are recreated by their daemons)
3. If you only need regular files, copy with a filter callback: { recursive: true, filter: (s) => !s.endsWith('.sock') }

Example fix

// before
fs.cp('/var/run/app', 'backup', { recursive: true }, cb); // hits a .sock file

// after
fs.cp('/var/run/app', 'backup', {
  recursive: true,
  filter: (src) => !fs.statSync(src).isSocket(),
}, cb);

const skipSockets = (src) => { const st = fs.lstatSync(src); return st.isDirectory() || st.isFile() || st.isSymbolicLink(); };

const isCopyableEntry = (st) => st.isFile() || st.isDirectory() || st.isSymbolicLink();

try { await fs.promises.cp(src, dest, { recursive: true, filter: isCopyablePath }); } catch (e) { if (e.code === 'ERR_FS_CP_SOCKET') { /* exclude *.sock and retry once */ } else throw e; }

When it happens

Trigger: fs.cp on /run or /var/run trees (or any dir) containing *.sock files with { recursive: true }; containerizing a volume that includes a live database socket (postgres/.s.PGSQL.5432, docker.sock); archiving a node_modules/.cache directory that contains IPC sockets.

Common situations: Recursive backup/copy scripts sweeping system directories; CI copying a runtime state directory; Docker/K8v volume mirroring where daemons left sockets behind.

Related errors

• ERR_FS_CP_FIFO_PIPE
• ERR_FS_CP_DIR_TO_NON_DIR
• ERR_FS_CP_EEXIST
• ERR_FS_CP_EINVAL
• ERR_FS_CP_NON_DIR_TO_DIR

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/d3bbd8e218fd4d64. Report an issue: GitHub.

Appendix: source

Thrown at ext/node/polyfills/_fs/cp/cp.ts:100

      });
    case "EEXIST":
      throw new ERR_FS_CP_EEXIST({
        message: err.message,
        path: err.path,
        syscall: "cp",
        errno: EEXIST,
        code: "EEXIST",
      });
    case "EISDIR":
      throw new ERR_FS_EISDIR({
        message: err.message,
        path: err.path,
        syscall: "cp",
        errno: EISDIR,
        code: "EISDIR",
      });
    case "SOCKET":
      throw new ERR_FS_CP_SOCKET({
        message: err.message,
        path: err.path,
        syscall: "cp",
        errno: EINVAL,
        code: "EINVAL",
      });
    case "FIFO":
      throw new ERR_FS_CP_FIFO_PIPE({
        message: err.message,
        path: err.path,
        syscall: "cp",
        errno: EINVAL,
        code: "EINVAL",
      });
    case "UNKNOWN":
      throw new ERR_FS_CP_UNKNOWN({
        message: err.message,
        path: err.path,

View on GitHub (pinned to 9ad36f7a2c)