  The Belle II experiment at the SuperKEKB $e^{+}e^{-}$ collider in KEK, Japan,
started physics data-taking with a complete detector from early 2019 with the
primary physics goal of probing new physics in heavy quark and lepton decays.
An online trigger system is indispensable for the Belle II experiment to reduce
the beam background events associated with high electron and positron beam
currents without sacrificing the target physics-oriented events. During the
Belle II operation upon beam collision, the trigger system must be consistently
controlled and its status must be carefully monitored in the process of data
acquisition against unexpected situations. For this purpose, we have developed
a slow control system for the Belle II trigger system. Around seventy thousand
configuration parameters are saved in the Belle II central database server for
every run when a run starts and stops. These parameters play an essential role
in offline validation of the quality of runs. Around three thousand real-time
variables are stored in the Belle II main archiving server, and the trend of
some of these variables are regularly used for online and offline monitoring
purposes. Various operator interface tools have been prepared and used. When
the configuration parameters are not correctly applied, or some of the
processes are unexpectedly terminated, the slow control system detects it,
stops the data-taking process, and generates an alarm. In this article, we
report how we constructed the Belle II trigger slow control system, and how we
successfully managed to operate during its initial stage.
