lima-vm/lima · error

failed to detect the format of %#q: %w

Error message

failed to detect the format of %#q: %w

What it means

validateDiskFormat opens the disk image and asks qcow2reader to detect its format; if the file is unreadable as a known image format (or I/O fails), Lima wraps the underlying error. This means the additional disk / cidata file passed to the vz driver is not a recognizable disk image.

Source

Thrown at pkg/driver/vz/vm_darwin.go:537

			if err != nil {
				return err
			}
			configurations = append(configurations, networkConfig)
		}
	}
	vmConfig.SetNetworkDevicesVirtualMachineConfiguration(configurations)
	return nil
}

func validateDiskFormat(diskPath string) error {
	f, err := os.Open(diskPath)
	if err != nil {
		return err
	}
	defer f.Close()
	img, err := qcow2reader.Open(f)
	if err != nil {
		return fmt.Errorf("failed to detect the format of %#q: %w", diskPath, err)
	}
	supportedDiskTypes := []image.Type{raw.Type, asif.Type}
	if t := img.Type(); !slices.Contains(supportedDiskTypes, t) {
		return fmt.Errorf("expected the format of %#q to be one of %v, got %#q", diskPath, supportedDiskTypes, t)
	}
	// TODO: ensure that the disk is formatted with GPT or ISO9660
	return nil
}

func attachDisks(ctx context.Context, inst *limatype.Instance, vmConfig *vz.VirtualMachineConfiguration) error {
	diskPath := filepath.Join(inst.Dir, filenames.Disk)
	isoPath := filepath.Join(inst.Dir, filenames.ISO)
	ciDataPath := filepath.Join(inst.Dir, filenames.CIDataISO)
	var configurations []vz.StorageDeviceConfiguration

	if osutil.FileExists(diskPath) {
		if err := validateDiskFormat(diskPath); err != nil {
			return err

View on GitHub (pinned to dd909d0973)

Solutions

1. Inspect the file (`file <path>`, `qemu-img info`) and re-create or re-download the disk image in a supported format
2. Ensure the path passed as additional disk actually points to the data disk (datadisk file) and is non-empty
3. Delete the instance/disk store entry and let Lima recreate the disk

f, err := os.Open(diskPath)
if err != nil { return err }
magic := make([]byte, 8)
f.Read(magic)
// verify magic matches a known image type or run `file diskPath` before attach

if err := limactlStart(cfg); err != nil {
    if strings.Contains(err.Error(), "failed to detect the format") {
        // re-download / recreate the disk image
    }
}

When it happens

Trigger: attachDisks -> validateDiskFormat on a disk path whose file is corrupted, empty, truncated, or in an unsupported format that qcow2reader.Open cannot sniff.

Common situations: Interrupted download/copy of a disk image; a placeholder or text file at the disk path; disk created by another tool in a format qcow2reader does not detect; permission/IO error during open that surfaces after Open.

Related errors

• expected the format of %#q to be one of %v, got %#q
• resolving filesystem root tree OID %d: %w
• resolving path %#q: %w
• chown inode %d (%#q): %w
• read block 0: %w

AI-assisted analysis of lima-vm/lima@dd909d0973 (2026-09-01). Data as JSON: /api/errors/d73ecb25608c5dbc. Report an issue: GitHub.