I recently had a problem where one of the daemons run at startup would hang.  In order to disable this, I needed to boot into single user mode, and chkconfig the service off.

The key to booting into single user mode is the word ‘single’ on the kernel command line.

Heres the steps:

1. Reboot the system
2. At the grub screen, hit esc to stop the default boot sequence
3. use the arrow keys select the kernel image you wish to boot
4. type ‘e’ to edit the kernel image startup parameters
5. on the screen use the arrow keys again to select the line with the startup parameters.  This should be the  the middle line, the one that starts with the word ‘kernel’.
6. Type ‘e’ to edit this line
7. append the word ‘single to the end of the line and type enter
8. type the ‘b’ key to boot the kernel