HP-UX: Boot Into Single User Mode

Question: I know how to boot into single user mode under Linux and FreeBSD. But, how do I boot into single user mode under HP-UX (HP9000) UNIX operating system?

Answer:. First, you need to interrupt the boot process when prompted. This is useful to reset password and other tasks.
First, you need to tell HP-UX box to boot primary, it should give you a prompt to interact with the ISL. You should reply 'y' to this. Once at ISL> prompt type hpux -is or hpux -iS /stand/vmunix to boot into single user mode.

Booting HP-UX UNIX into Single User Mode

Use the following procedure to boot into single-user mode in HP-UX.
Interrupt the boot process when prompted by pressing [ESCAPE] key. You will see message as follows:

Selecting a system to boot. To stop selection process, press and hold the ESCAPE key... 

OR

Autoboot from primary boot path enabled.
To override, press any key within 10 seconds.

Type boot pri isl at the prompt:
boot pri
At the ISL> prompt:, type
hpux -is /stand/vmunix
OR
hpux -is
In above example, the -i option is used to make the system come up in run-level s, for single user mode of operation. /stand/vmunix is optional but some time required. Usually, 'hpux -is' is more than enough to boot into single user mode.
hpux is the HP-UX specific secondary system loader (SSL) utility for bootstrap. See man page for more information.