I want my linux server to automatically shutdown at some specific time and start again based on time specified. The intention here is to save the power in night time. I know there are some options available to control the power used by monitor, HDD etc but have not analyzed how much power will be saved on that.
If your network card supports WoL (Wake on LAN) then configure the BIOS to do that and (of course, test) then I would probably suggest a small shell script running the shutdown command and run in a cron job should do the trick...
Shutdown should be no problem, but getting the server to start automatically can cause problems. This depends on your BIOS. Some BIOS have the option to automatically start at a given time, but often that isn't available in servers.
If the server is from a big company like HP, then check if it already has, or can be upgraded with an ILO card (that's the HP/Compaq option, I don't know what other manufacturers have). This is a PCI card which is n fact a small PC complete with NIC, VGA, Keyboard and mouse input, and also an external power input. With these cards you can remotely control a server and turn it off and back on if necessary. This card uses a lot less power than the actual server.