docker/cli · error

invalid device cgroup format '%s'

Error message

invalid device cgroup format '%s'

What it means

Error "invalid device cgroup format '%s'" thrown in docker/cli.

Source

Thrown at cli/command/container/opts.go:1051

	}

	return container.DeviceMapping{
		PathOnHost:        src,
		PathInContainer:   dst,
		CgroupPermissions: permissions,
	}, nil
}

// validateDeviceCgroupRule validates a device cgroup rule string format
// It will make sure 'val' is in the form:
//
//	'type major:minor mode'
func validateDeviceCgroupRule(val string) (string, error) {
	if deviceCgroupRuleRegexp.MatchString(val) {
		return val, nil
	}

	return val, fmt.Errorf("invalid device cgroup format '%s'", val)
}

// validDeviceMode checks if the mode for device is valid or not.
// Valid mode is a composition of r (read), w (write), and m (mknod).
func validDeviceMode(mode string) bool {
	legalDeviceMode := map[rune]bool{
		'r': true,
		'w': true,
		'm': true,
	}
	if mode == "" {
		return false
	}
	for _, c := range mode {
		if !legalDeviceMode[c] {
			return false
		}
		legalDeviceMode[c] = false

View on GitHub (pinned to e9452d6e78)

When it happens

Trigger: Thrown at cli/command/container/opts.go:1051 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01). Data as JSON: /data/errors/c4c2a4c6df6050dc.json. Report an issue: GitHub.