How to reboot Solaris UNIX machine or server using the command/shell prompt?

You can use any one of the following commands. First login as root user (or use su – to become a root).

Once logged in as root type the reboot command to reboot the system:
# reboot
You can use schedule reboot with the shutdown command. The following will reboot Solaris box in 180 seconds with a message:

shutdown -y -i6 -g 180 " ==== Rebooting for kernel and apps upgrades ====="

You can also reboot using a specific disk and/or kernel. The following example reboots using a specific disk called disk2 and kernel:

reboot "disk2 kernel.build-k2/unix"