hashicorp/nomad · error

error writing to file %q: %w

Error message

error writing to file %q: %w

What it means

streamAllocDir copies files from a previous allocation's data directory (snapshot tar stream read via a tar.Reader) into the new allocation's directory. This error wraps any failure from f.Write while extracting the tar entry, and includes the destination file name and the underlying OS error.

Source

Thrown at client/allocwatcher/alloc_watcher.go:677

				return fmt.Errorf("error chmoding file %w", err)
			}

			// Can't change owner if not root or on Windows.
			if euid == 0 {
				if err := f.Chown(hdr.Uid, hdr.Gid); err != nil {
					f.Close()
					return fmt.Errorf("error chowning file %w", err)
				}
			}

			// We write in chunks so that we can test if the client
			// is still alive
			for !canceled() {
				n, err := tr.Read(buf)
				if n > 0 && (err == nil || err == io.EOF) {
					if _, err := f.Write(buf[:n]); err != nil {
						f.Close()
						return fmt.Errorf("error writing to file %q: %w", f.Name(), err)
					}
				}

				if err != nil {
					f.Close()
					if err != io.EOF {
						return fmt.Errorf("error reading snapshot: %w", err)
					}
					break
				}
			}

		}
	}

	if canceled() {
		return ctx.Err()
	}

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Check disk space and inode availability on the client's alloc_dir volume (df -h / df -i).
2. Inspect the destination file path and its permissions/ownership; ensure the nomad user can write to alloc_dir.
3. Verify no symlinks in the previous alloc's data escape the alloc directory (Nomad rejects these); clean up the old alloc dir.
4. Retry the allocation migration after freeing space or fixing permissions; a failed migration will be rescheduled.

Example fix

// before (server-side fix is not possible; caller-side remedy)
// client hits: error writing to file "/data/alloc/.../app.log": write ...: no space left on device
// after
$ df -h /data/alloc  # free space or expand volume, then restart the failed allocation

// before enabling alloc migration on a client, precheck the target volume
if err := checkWritable(conf.AllocDir); err != nil {
    return fmt.Errorf("alloc dir not writable, migration would fail: %w", err)
}
func checkWritable(dir string) error {
    probe := filepath.Join(dir, ".nomad-write-probe")
    if err := os.WriteFile(probe, []byte("ok"), 0o600); err != nil { return err }
    return os.Remove(probe)
}

When it happens

Trigger: During alloc migration (migrateAllocDir), a tar entry read from the previous allocation's snapshot is written to the new alloc dir and the write fails — typically disk full, permission denied on the destination path, a bad symlink target escaping the alloc dir, or the destination file being closed/unwritable.

Common situations: Disk quota or out-of-space on the client's alloc_dir volume; corrupted or malicious symlink entries in a previous alloc's data (the BadSymlink tests exercise exactly this); read-only filesystem; file previously created with restrictive permissions by another user.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• unable to read rooted allocation directory
• can't seek to offset %d: %w
• Couldn't copy %q to %q: %w
• error reading snapshot: %w
• failed to list entries: %v

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/906a10fd285a2603. Report an issue: GitHub.