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Linux Foundation offers a free course through edx, Introduction to Linux (LFS101)
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@alchemix online book recommendation.
- As you are working through the book online or the class, you might like to visit the unofficial Bash FAQ or one of the GNU manuals.
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Most programs and/or desktops have a home site with documentation and maybe some tutorials, as do distributions.
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Learn to use the man command.
A problem with the more generalized books for linux is that they are specific to a distribution, the material is quickly outdated, and most of it is online already.