Some problems cannot be fixed through the operating system, for example, not remembering the root password or changes to configuration files that prevent the system from booting. Solaris allows booting from the CD-ROM into single user mode, which will allow you to mount your filesystems and repair the problem.
To boot into single user mode from CD-ROM, from the ok (bootprom) prompt, use the following:
boot cdrom -s
This will give you a root prompt (#) with a functional but limited Solaris filesystem from the CD-ROM. To access your filesystems, you need to mount them. For example, if your root filesystem is c0t0d0s0, use as follows:
mount /dev/dsk/c0t0d0s0 /mnt
Then you can work in the /mnt filesystem and make changes to your real root filesystem. You can mount other filesystems on their usual mount points within the root (/mnt) filesystem. Once you have fixed whatever you need, just reboot.