Link: http://forums.gentoo.org/viewtopic-p-5688968.html#5688968

For those who wish to have their nix screen locked manually or automatically and dont want to install big/bloated screen saver applications here are 3 good very light and minimal solutions:

For X:

• xtrlock 
  Size of files: 7 kB 
  Homepage: http://ftp.debian.org/debian/pool/main/x/xtrlock/
  Description: A simplistic screen locking program for X
  License: GPL-2

For TTY:

• vlock 
  Size of files: 53 kB
  Homepage: http://cthulhu.c3d2.de/~toidinamai/vlock/vlock.html
  Description: A console screen locker
  License: GPL-2
  

And to make it work with a timer:

• xautolock  
  Size of files: 32 kB
  Homepage: http://www.ibiblio.org/pub/Linux/X11/screensavers/
  Description: An automatic X screen-locker/screen-saver.
  License: GPL-2

Here goes an example:

$  xautolock -locker xtrlock -time 5

xautolock will tell  ( locker) xtrlock to activate after 5 minutes idle

For help type:

$ xautolock -help

Adding it to your Window Manager like fluxbox startup :

$ echo xautolock -locker xtrlock -time 5 >> .fluxbox/startup