I wanted to monitor what happens when a test user logs in to my CentOS 6.4 system, so I tried this to poll ps for /bin/login and strace the pid when it appears:until [[ $(ps -ef|grep -q [l]ogin)$? -eq 0 ]]; do     true; done && strace pidof /bin/loginI SSH'd in from another system and checked on the system, but no strace ever happened.  Why doesn't login show up in ps?  the user's shell is bash and it connects without a problem.
Why doesn't /bin/login appear in ps output when someone is logging in
bash;login;strace
Because in your sshd_config file, you don't have UseLogin yes. The default is no. From the manual page:UseLogin        Specifies whether login(1) is used for interactive login ses        sions.  The default is no.  Note that login(1) is never used        for remote command execution.  Note also, that if this is        enabled, X11Forwarding will be disabled because login(1) does not        know how to handle xauth(1) cookies.  If UsePrivilegeSeparation        is specified, it will be disabled after authentication.