Single user mode.

Before bringing your machine is single user mode
Make sure
1)you inform other users logged in about the event using wall command.
2)If you are sharing a files using NFS protocol Make sure you disable network access to shared file systems using exportfs -ua.
3)Make sure no critical process such as backupjobs are running in background.
4)run.
#/sbin/telinit 1
5)confirm the runlevel using runlevel command.

Here is a different way of doing it at system boot.

http://www.cyberciti.biz/faq/grub-boot-into-single-user-mode/

Here are some issues faced by me during single user mode.

http://www.unix.com/unix-dummies-questions-answers/155269-not-able-log-into-single-user-mode.html

http://www.linuxquestions.org/questions/showthread.php?p=4277312&posted=1#post4277312