- FreeBASIC gives me an error 'ld: can't find -lX11' or something similar!
- How do I install FreeBASIC in Ubuntu?

FreeBASIC uses ld to link its files under linux. This program requires that any libraries you use have the '-dev' versions installed. For example, for the above error message, you'd want to install xlib-dev for your distribution. Other common errors are for glibc, which requires glibc-dev, and sdl, which requires sdl-dev. Most distributions make these easily available on your install media.

See This thread in the FB forums