According to Kushiki-ryo (law on state documentary forms in the Yoro Code) (Hyakkan-tonoi no jo (百官宿直条, the article of Tonoi for all the officials)) all the Kanshi (government officials) except Dainagon (chief councilor of state) or higher officials and ministers of Hassho (eight ministries and agencies) were supposed to assume the obligation of Tonoi in alternate shifts for the section to which they belonged.
公式令（百官宿直条）によれば、大納言以上及び八省卿を除く全ての官人に対して、その所属する官司に対して交代で宿直する義務を負った。