There are two sets of APIs that allow user accounting data to be accessed by applications. The preferred set of programming interfaces for accessing and manipulating user accounting information is described on the getutxent(3C) man page. These are both more capable and more portable than the older getutent(3C) routines.
Older applications may access the underlying accounting files directly. The files /var/adm/utmp and /var/adm/wtmp, and the corresponding symbolic links /etc/utmp and /etc/wtmp may be removed in a future release. The format of the data contained in these files constrain the future evolution of the Solaris operating environment. Applications using these files should be updated to use the documented and supported APIs.
Applications that are already using the getutent(3C) family of routines may be unaffected on small system configurations. However, in future releases these interfaces may return errors when used on very large system configurations. For this reason, use the getutxent(3C) routines for both old and new code in place of the getutent(3C) APIs.