6.7.2 Shutdown programs
# shutdown -r +10 - reboot in 10 minutes.
SunOS 5.X, which uses a different shutdown program. This program is a shell script to take you to the desired run state and is located in /usr/sbin. You can specify a grace period (-g) in seconds, a run level (-i), and auto-confirmation of answers (-y). So to halt the system in 2 minutes while warning the users of the impending shutdown execute:
# shutdown -y -g120 -i0