C# Definition:

  /// <summary>
  /// Describes the reasons a restart of the system is needed.
  /// </summary>
  public enum RM_REBOOT_REASON : uint
  {
    /// <summary>
    /// Reboot not required.
    /// </summary>
    RmRebootReasonNone = 0x0,

    /// <summary>
    /// Current user does not have permission to shut down one or more detected processes.
    /// </summary>
    RmRebootReasonPermissionDenied = 0x1,

    /// <summary>
    /// One or more processes are running in another TS session.
    /// </summary>
    RmRebootReasonSessionMismatch = 0x2,

    /// <summary>
    /// A critical process has been detected.
    /// </summary>
    RmRebootReasonCriticalProcess = 0x4,

    /// <summary>
    /// A critical service has been detected.
    /// </summary>
    RmRebootReasonCriticalService = 0x8,

    /// <summary>
    /// The current process has been detected.
    /// </summary>
    RmRebootReasonDetectedSelf = 0x10
  }