docker/compose · error

adding files to tar: %w

Error message

adding files to tar: %w

What it means

tarArchive runs ArchiveBuilder in a goroutine writing into an io.Pipe. If collecting/walking/writing entries fails (any of errors 103-111), the pipe is closed with 'adding files to tar: %w', which surfaces on the reading side — typically as the Untar/put-archive call failing with this message for every container being synced.

Source

Thrown at internal/sync/tar.go:327

			info:   info,
			header: header,
		})

		return nil
	})
	if err != nil {
		return nil, err
	}
	return result, nil
}

func tarArchive(ops []PathMapping) io.ReadCloser {
	pr, pw := io.Pipe()
	go func() {
		ab := NewArchiveBuilder(pw)
		err := ab.ArchivePathsIfExist(ops)
		if err != nil {
			_ = pw.CloseWithError(fmt.Errorf("adding files to tar: %w", err))
		} else {
			// propagate errors from the TarWriter::Close() because it performs a final
			// Flush() and any errors mean the tar is invalid
			if err := ab.Close(); err != nil {
				_ = pw.CloseWithError(fmt.Errorf("closing tar: %w", err))
			} else {
				_ = pw.Close()
			}
		}
	}()
	return pr
}

// Dedupe the entries with last-entry-wins semantics.
func dedupeEntries(entries []archiveEntry) []archiveEntry {
	seenIndex := make(map[string]int, len(entries))
	result := make([]archiveEntry, 0, len(entries))
	for i, entry := range entries {

View on GitHub (pinned to ddc4b044b6)

Solutions

1. Unwrap the %w — the inner error is one of errors 103-111 and names the real host-side problem; fix that first
2. Check whether the named host tree was mid-rewrite (build running) and re-sync when idle
3. Fix local permissions on the sync root (see 103/110)
4. Do not restart containers in response to this error appearing everywhere at once — it is a local-side failure

// validate the archive can be built before syncing to any container (dry-run into io.Discard)
if err := NewArchiveBuilder(io.Discard).ArchivePathsIfExist(paths); err != nil { return err }

// on 'adding files to tar', unwrap the inner error (one of errors 103-111), fix the named host path, then retry — do not touch the containers

When it happens

Trigger: ArchivePathsIfExist returning an error in the producer goroutine: unreadable paths (103/110), vanished or mid-write files (104-109), or relative-path computation failures (111). The message appears on the consumer side of the pipe, often for all 16 parallel container copies at once.

Common situations: compose watch failing on all replicas simultaneously with the same wrap — the tell that the local archive build, not the containers, is broken; usually triggered by source-tree churn or permissions.

Related errors

• writing %q header: %w
• closing tar: %w
• stat %q: %w
• deleting paths in %s: %w
• copying files to %s: %w

AI-assisted analysis of docker/compose@ddc4b044b6 (2026-08-15). Data as JSON: /api/errors/bb8c1892efac0241. Report an issue: GitHub.