What causes "Cannot copy a FIFO pipe" in denoland/deno?

Add a filter that skips FIFOs: check stats.isFIFO()

denoland/deno · error · NodeSystemError

ERR_FS_CP_FIFO_PIPE

ERR_FS_CP_FIFO_PIPE

Error message

Cannot copy a FIFO pipe

What it means

Mirror of the socket case: kind 'FIFO' from the native cp validation becomes ERR_FS_CP_FIFO_PIPE ('Cannot copy a FIFO pipe'). Named pipes (created with mkfifo) have a reader/writer semantic, not stored bytes, so copying their 'content' is meaningless and fs.cp rejects them.

Source

Thrown at ext/node/polyfills/_fs/cp/cp.ts:108

      });
    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,
        syscall: "cp",
        errno: EINVAL,
        code: "EINVAL",
      });
    case "SYMLINK_TO_SUBDIRECTORY":
      throw new ERR_FS_CP_SYMLINK_TO_SUBDIRECTORY({
        message: err.message,
        path: err.path,

View on GitHub (pinned to 89f33cbef2)

Solutions

Add a filter that skips FIFOs: check stats.isFIFO()
Exclude runtime/FIFO directories from the copy set explicitly
Delete stale FIFOs before deploying over them

Example fix

// before
await fsp.cp(runDir, backupDir, { recursive: true, dereference: true });

// after
await fsp.cp(runDir, backupDir, {
  recursive: true,
  dereference: true,
  filter: async (s) => !(await fsp.lstat(s)).isFIFO(),
});

Defensive patterns

Strategy: validation

Validate before calling

const filter = async (s) => !(await fsp.lstat(s)).isFIFO();
await fsp.cp(src, dest, { recursive: true, dereference: true, filter });

Type guard

async function isFifoPath(p) { try { return (await fsp.lstat(p)).isFIFO(); } catch { return false; } }

Try / catch

try { await fsp.cp(src, dest, { recursive: true, dereference: true }); } catch (e) { if (e.code === 'ERR_FS_CP_FIFO_PIPE') { /* skip FIFO and retry */ } else throw e; }

Prevention

Filter out FIFOs on any recursive copy over runtime or fixture dirs
Recreate named pipes with mkfifo at the destination when needed
Audit test fixtures for special files before packaging

When it happens

Trigger: Recursive copy with dereference over a directory containing FIFOs (e.g. mpd's control pipe, logging pipes under /run); deploying a tree that includes a fixture FIFO created by a test.

Common situations: Packaging scripts that snapshot service runtime directories; CI caches containing named pipes created by integration tests.

Related errors

AI-assisted analysis of denoland/deno@89f33cbef2 (2026-08-16). Data as JSON: /api/errors/48a667fefd58f324. Report an issue: GitHub.