GNU gtypist. Got me from "hunt and peck" to touch typing with a decent wpm count within 2 weeks. Considering I used fewer than half of the tutorials, I think that's pretty awesome. It's an old GNU utility so it should be in any repos. Even had it on Cygwin.

Ktouch is awesome, Free, and in the Deb repo's, maybe others. Simple, effective, nice UI, and you can learn any layout from Qwerty to Colemak.

Klavaro Touch Typing Tutor is pretty good - Linux and OSX.

http://klavaro.sourceforge.net/en/

I used some random type tutor software in high school (sometime in the mid-late 90s), though only spent enough time with it to learn the home keys. I would then look at the keyboard for the remainder of the keys. Initially that was probably no faster than my old hunt and peck method. I remember remarking at one stage that I was looking at the keyboard out of habit. Then one day I noticed that I was no longer looking at all. I'm sure it was a strange feeling at the time!

Goes to show you don't really need to learn the whole process with some type tutor software. Though in terms of efficiency you may want to be aware of what they suggest. For instance, I think I was hitting the Y key with my left hand rather than right hand at some stage, but long ago changed that.

When I forced myself to learn touch-typing with a qwerty keyboard i used gtypist. I found it to be sufficient for its purpose.

The only gripe i had with it was that it required typing two spaces after a period. I found this just plain weird, so I fixed it in the tutorial files.

I guess using a blank keyboard also helped quite a bit..

In an article called "Learning Unix", I think recommending (I assume proprietary) Windows/Mac software, is a bit silly.