def update(self, pkg=None):
        ayum = yum.YumBase()
        ayum.doGenericSetup()
        ayum.doRepoSetup()
        try:
            ayum.doLock()
            if pkg != None:
                tx_result = ayum.update(pattern=pkg)
            else:
                tx_result = ayum.update()

            ayum.buildTransaction()
            ayum.processTransaction(
                    callback=DummyCallback())
        finally:
            ayum.closeRpmDB()
            ayum.doUnlock()
        return map(str, tx_result)