To spread awareness and familiarity with the Linux OS, on August 1st the Linux Foundation is temporarily offering a free online course and certification program on edX that usually costs around $2,400 on their own training website.
The course is entirely self-paced and online. Here is an outline of the course, and what to expect, though the edX version might be slightly different.
If you can't commit to all the lectures and tests, you can simply audit the class. Otherwise, you can get a certificate from the Linux Foundation—something that won't look to shabby on a résumé.
In conjunction with OTW's awesome Linux guides here in Null Byte, you can get a pretty damn good grasp on the most powerful system in the world.