The title can't be more specific. I'd like you to suggest the best way to send the poweroff instruction, to windows or Linux.
If your network card can use Wake-On-LAN and/or is supported, and is remotely accessible, then yes, it is quite possible to achieve it (wake-on-lan apps are in abundance on the play store), taking into account of security considerations which is outside of the scope of this site, double check and make sure no other service is on that public facing PC otherwise bad guys will get in and wreak havoc.
At the moment I'm using WOLdroid WOL Wake On Lan On remote.host execute:
Detect your remote.host's ehternet board usualy eth0 and save the HW Adress value XX:XX:XX:XX:XX:XX:XX
Enter that number when WOLdroid asks you for a mac adress. And your done.
Now you're able to powerup remotely
1. Prepare the Remote Host:
Remote host with Ubuntu 12.04
Create your private and public key files
To follow these steps you'll have to access your remote host, physically, or using another computer. I'll describe this as if you have physical access to the remote.host
Open a command window and install the ssh protocol:
Create public and private keys using ssh-key-gen
You should save the generated key in:
Press enter twice to leave the passphrase empty.
Now copy the id_rsa.pub to your ~/.ssh/authorized_keys file with this command:
Now you have to be able to execute the sudo shutdown -P 0 with no password.
Modify /etc/sudoers on remote.host with visudo
That way user "yourusername" can execute the shutdown command with no password asked.
By running visudo, it leads to edit /etc/sudoers.
Now we are able to access remotely, and shutdown without passwords asked.
2. Prepare your Android
Now you can Turn on and Shutdown a remote.host :)