i am currently doing my final year project.and as a module in that i need to lock the keyboard,mouse and the system when the user gets away from the system and resume them to normal state when the user comes back.i use a bluetooth phone as a token for the user.using python i check for the users presence.if the communication between phone and the system(laptop) breaks i need to lock mouse,keyboard and system.
for that i need to lock mouse,keyboard and the system individually so that someone cannot give any input via mouse or keyboard.so please tell me how to lock mouse,keyboard and system individually using a program.i am using ubuntu.i dont want the user to enter any password when he returns.the system will automatically detect him when he returns.

Can you please explain what exactly you want to do? You must provide us with much more details if you want us to help you.

Also, what distro are you using? Please put this information in your profile.

--Ian

If you use KDE for your desktop there is a Lock applet that you can add to the panel. Just right-click on an empty part of the panel, then in the drop-down (drop-up?) menu, click "Add applet to panel", then select the Lock/logout applet, or whatever Lock applet you have there.

When you click the Lock applet, your screen will go into screensaver mode and you will need to type in your password to unlock it. After one of my cats deleted a year's worth of email by walking on the keyboard, I never turn my back for a moment without now locking it!

For a generic solution, run xscreensaver-demo and use menu File->Lock Screen Now. (There used to be xlock, but it's not installed by default in Ubuntu Dapper, so I assume it's obsolete.)

You probably ought to find the easier way you're meant to use. On Ubuntu / Gnome, it's menu System -> Quit... -> Lock Screen.