Binary Compatibility Guide

/etc/utmp /var/adm/wtmp

These files hold user and accounting information for commands such as who, write, and login. In Solaris 2.x, each of these files has been replaced with a pair of files: /etc/utmp has been replaced with /var/adm/utmp and /var/adm/utmpx, and /var/adm/wtmp with /var/adm/wtmp and /var/adm/wtmpx. When an application opens one of these files, it receives the concatenation of its two new counterparts.

Note -

Symbolic links to these files are no longer supported. This is, if an application creates a link to /etc/utmp or /var/adm/wtmp, and attempts to open the symbolic link, the open call fails.