You press ⌘ S on startup in order to enter Single User Mode...but how do you then exit it safely?
Getting Out of Single-user mode:
exit - Continue the boot process (i.e. go to multi-user mode). Note that if you've made any significant
changes (or started any daemons, run SystemStarter, or anything like that), it's safer to reboot instead.
reboot - Reboot the computer.
shutdown -h now - Shut the computer down.
