utmp, wtmp - utmp and wtmp database entry formats
#include <utmp.h> /var/adm/utmp /var/adm/wtmp
The utmp and wtmp database files are obsolete and are no longer present on the system. They have been superseded by the extended database contained in the utmpx and wtmpx database files. See utmpx(5).
It is possible for /var/adm/utmp to reappear on the system. This would most likely occur if a third party application that still uses utmp recreates the file if it finds it missing. This file should not be allowed to remain on the system. The user should investigate to determine which application is recreating this file.