Can i turn on, logout, login one ubuntu pc from another ubuntu pc through remote desktop.
I have also try remote desktop but i can only when pc is turn on.
You'll only be able to connect to your PC whenever it's on, because if it's off, then there's nothing running on the machine to contact to and there's no network active. A device in a powered off state is really off, you see. Similarly - your can't receive phone calls on your mobile phone without it having turned on. Some software can't do magic here.
However, I know of two techniques exist to manage the power without the machine being turned on, although it needs the wall socket power to be connected of course.
Wake on LAN. It's a feature of your network card - it will listen to "magic packets" to arrive on the interface to trigger a "power on" event on the PCI bus. It needs some standby power and another device in the same local network to be able to send such magic packets. So, basically, you'll have to
configure your BIOS to listed to WoL events.
have a network card that supports this.
configure your network card to do so (see manpage of ethtool).
have some device connected to the internet fire up the PC by sending the magic packet on the local network.
Major limitation: no available directly over the internet.
Out of Band management module. Some motherboards, mostly server and business-line desktop machines feature the Intel vPro with AMT. In servers you'll notice most have a dedicated card for this - HP iLO, Dell iDRAC, etc. With such a module you'll be able to control power (and usually more). See the manual of your desktop if you have it and how that works.
Major limitation: hardware requirements.
After the machine has been powered on with one of the techniques above, you'll have to make sure your remote desktop server (e.g. VNC server, NX server, etc.) is started and the network is automatically connected properly, so you can connect to it.
Powered off → unreachable.
You'll only be able to connect to your PC whenever it's on, because if it's off, then there's nothing running on the machine to contact to and there's no network active. A device in a powered off state is really off, you see. Similarly - your can't receive phone calls on your mobile phone without it having turned on. Some software can't do magic here.
However, I know of two techniques exist to manage the power without the machine being turned on, although it needs the wall socket power to be connected of course.
Wake on LAN. It's a feature of your network card - it will listen to "magic packets" to arrive on the interface to trigger a "power on" event on the PCI bus. It needs some standby power and another device in the same local network to be able to send such magic packets. So, basically, you'll have to
ethtool).Major limitation: no available directly over the internet.
See also:
Out of Band management module. Some motherboards, mostly server and business-line desktop machines feature the Intel vPro with AMT. In servers you'll notice most have a dedicated card for this - HP iLO, Dell iDRAC, etc. With such a module you'll be able to control power (and usually more). See the manual of your desktop if you have it and how that works.
Major limitation: hardware requirements.
After the machine has been powered on with one of the techniques above, you'll have to make sure your remote desktop server (e.g. VNC server, NX server, etc.) is started and the network is automatically connected properly, so you can connect to it.