Как systemd просит юниты перезагрузить конфигурацию?

Вот что на странице руководства systemd.service говорит о перезарядке:

       ExecReload=
           Commands to execute to trigger a configuration reload in the 
           service. This argument takes multiple command lines, following
           the same scheme as described for ExecStart= above. Use of
           this setting is optional. Specifier and environment variable
           substitution is supported here following the same scheme as
           for ExecStart=.

           One additional, special environment variable is set: if known,
           $MAINPID is set to the main process of the daemon, and may
           be used for command lines like the following:

               /bin/kill -HUP $MAINPID

           Note however that reloading a daemon by sending a signal
           (as with the example line above) is usually not a good
           choice, because this is an asynchronous operation and hence
           not suitable to order reloads of multiple services against
           each other. It is strongly recommended to set ExecReload=
           to a command that not only triggers a configuration reload
           of the daemon, but also synchronously waits for it to complete.

(Единственный способ узнать, что systemd.service правильная страница руководства для поиска была в Google для ExecReload, строка, которую я догадался, покопавшись в исходном коде Systemd.)