AC - the tool to count the connect time of specific users, it's real useful when we need to check whether the user has login and how long he or she logins to the terminal, I encourage people to look at the unix standard tool when comes to system monitoring because all those tools are available in every single variant of unix alike system. Here's how I make use of ac.
Total time of user root at ttyp1
shell>ac -t ttyp1 root
Total time of user by day/24 hours scale of user root at ttyp1
shell>ac -d -t ttyp1 root
Feb 22 total 10.12
Feb 23 total 37.19
Feb 24 total 14.18
Totaly time of all users
This is a quickie to help system administrator so that they manage to check on the login users easily.