def upgrade(reboot=False, at_time=None):
    '''
    Upgrade the kernel and optionally reboot the system.

    reboot : False
        Request a reboot if a new kernel is available.

    at_time : immediate
        Schedule the reboot at some point in the future. This argument
        is ignored if ``reboot=False``. See
        :py:func:`~salt.modules.system.reboot` for more details
        on this argument.

    CLI Example:

    .. code-block:: bash

        salt '*' kernelpkg.upgrade
        salt '*' kernelpkg.upgrade reboot=True at_time=1

    .. note::
        An immediate reboot often shuts down the system before the minion has a
        chance to return, resulting in errors. A minimal delay (1 minute) is
        useful to ensure the result is delivered to the master.
    '''
    result = __salt__['pkg.upgrade'](name=_package_name())
    _needs_reboot = needs_reboot()

    ret = {
        'upgrades': result,
        'active': active(),
        'latest_installed': latest_installed(),
        'reboot_requested': reboot,
        'reboot_required': _needs_reboot
    }

    if reboot and _needs_reboot:
        log.warning('Rebooting system due to kernel upgrade')
        __salt__['system.reboot'](at_time=at_time)

    return ret