lima-vm/lima · error

failed to mount %#q on %#q: %w (output=%#q)

Error message

failed to mount %#q on %#q: %w (output=%#q)

What it means

Lima's macOS Mount() helper runs the external `mount` command with the given device, mountpoint, and options. This error wraps any non-zero exit of that command together with its combined stdout/stderr output, so the developer can see exactly why the kernel refused the mount.

Source

Thrown at pkg/osutil/mount_darwin.go:26

	"fmt"
	"os/exec"
	"strings"

	"github.com/sirupsen/logrus"
)

// Mount mounts the device.
// Root privileges is not necessary.
func Mount(ctx context.Context, fs, dev, mnt string, options []string) error {
	args := []string{"-t", fs}
	if len(options) > 0 {
		args = append(args, "-o", strings.Join(options, ","))
	}
	args = append(args, dev, mnt)
	cmd := exec.CommandContext(ctx, "mount", args...)
	logrus.Debugf("Executing command: %v", cmd.Args)
	if output, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("failed to mount %#q on %#q: %w (output=%#q)", dev, mnt, err, output)
	}
	return nil
}

func Umount(ctx context.Context, mnt string) error {
	cmd := exec.CommandContext(ctx, "umount", mnt)
	logrus.Debugf("Executing command: %v", cmd.Args)
	if output, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("failed to unmount %#q: %w (output=%#q)", mnt, err, output)
	}
	return nil
}

View on GitHub (pinned to dd909d0973)

Solutions

1. Read the `output=` portion of the error — it contains mount(8)'s own diagnostic (e.g. 'Resource busy', 'no such file or directory').
2. Ensure the device is attached (hdiutil attach / diskutil list shows it) and the mount point directory exists.
3. Check the mount point isn't already mounted (diskutil info <mnt>).
4. Confirm the process has permission (sudo) if the filesystem requires elevated mount.

Example fix

// before
os.MkdirAll /tmp/lima missing -> mount fails
// after
if err := os.MkdirAll(mnt, 0o755); err != nil { return err }
return osutil.Mount(ctx, dev, mnt, "cd9660")

// preflight before calling Mount
if _, err := os.Stat(dev); err != nil { return fmt.Errorf("device missing: %w", err) }
if fi, err := os.Stat(mnt); err != nil || !fi.IsDir() { return fmt.Errorf("mount point missing: %s", mnt) }

if err := osutil.Mount(ctx, dev, mnt, "cd9660"); err != nil {
    var exitErr *exec.ExitError
    if errors.As(err, &exitErr) {
        log.Errorf("mount failed: %s", strings.TrimSpace(extractOutput(err)))
    }
    return err
}

When it happens

Trigger: writeGuestFiles calls osutil.Mount on macOS and the `mount <flags> <dev> <mnt>` subprocess exits non-zero (bad device, missing mount point, permission denied, mount point already in use).

Common situations: Mounting a disk image before hdiutil attach completed; mount point directory missing; macOS SIP/permission prompts denying the operation; device already mounted elsewhere.

Related errors

• failed to create mount point %#q: %w
• failed to unmount %#q: %w (output=%#q)
• failed to create temp file: %w
• failed to write temp plist: %w
• failed to create a temporary file for signing QEMU binary: %

AI-assisted analysis of lima-vm/lima@dd909d0973 (2026-09-01). Data as JSON: /api/errors/8dc9f3ac64d733a9. Report an issue: GitHub.