juicedata/juicefs · error

open control file for %s: %s

Error message

open control file for %s: %s

What it means

warmup opens the mount's control file (via openController on the first resolved target path) to talk to the FUSE daemon for cache warming. If opening the control file fails — the mount point has no JuiceFS control interface, the daemon is unresponsive, or permission is denied — the error is wrapped as 'open control file for %s: %s'.

Source

Thrown at cmd/warmup.go:254

				logger.Warnf("Skipped path %q because it fails to get absolute path: %s", pathStr, e)
				continue
			}
			paths = append(paths, vfs.JoinTarget(abs, spec))
		}
		if err = scanner.Err(); err != nil {
			logger.Fatalf("Reading file %q failed with error: %s", fname, err)
		}
	}
	if len(paths) == 0 {
		logger.Infof("no path")
		return nil
	}

	// find mount point
	first, _, _, _ := vfs.SplitTarget(paths[0])
	controller, err := openController(first)
	if err != nil {
		return fmt.Errorf("open control file for %s: %s", first, err)
	}
	defer controller.Close()

	mp := first
	for ; mp != "/"; mp = filepath.Dir(mp) {
		inode, err := utils.GetFileInode(mp)
		if err != nil {
			logger.Fatalf("lookup inode for %q: %s", mp, err)
		}
		if inode == uint64(meta.RootInode) {
			break
		}
	}

	threads := ctx.Uint("threads")
	if threads == 0 {
		logger.Warnf("threads should be larger than 0, reset it to 1")
		threads = 1

View on GitHub (pinned to c9a67b23e8)

Solutions

1. Check the inner error after the colon (ENOENT vs EPERM vs timeout) to distinguish missing mount from permission issues.
2. Confirm the path is inside a live JuiceFS mount (`juicefs status <meta-url>` or check <mp>/.stats).
3. Ensure the FUSE device is available (/dev/fuse) and the mount is healthy; remount if the daemon is hung.
4. Run with sufficient permissions (the control file may be root-owned).

if _, err := os.Stat(filepath.Join(mp, ".control")); err != nil {
    return fmt.Errorf("no JuiceFS control file at %s: %w", mp, err)
}

controller, err := openController(first)
if err != nil {
    if os.IsPermission(err) { /* run with elevated perms or fix ownership */ }
    if errors.Is(err, os.ErrNotExist) { /* not a JuiceFS mount */ }
    return err
}
defer controller.Close()

When it happens

Trigger: `juicefs warmup <path>` where openController fails: path not on a JuiceFS FUSE mount, .control file missing or not accessible, or the FUSE daemon hung so the open times out.

Common situations: Warming caches on a subpath that is a different (non-JuiceFS) filesystem; mount in a crashed/zombie state; running without permission to open the control file; warmup invoked inside a container lacking the FUSE device.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

• write message: %s
• open control file for [%d:%s]: %w
• Unsupported ByteMultiple " + sMultiple
• wrong type
• random, backward, skip are only valid under read

AI-assisted analysis of juicedata/juicefs@c9a67b23e8 (2026-09-06). Data as JSON: /api/errors/69d4771fe05cc276. Report an issue: GitHub.