http://unix.stackexchange.com/questions?sort=votes
Good source for learning with most popular questions about Linux.
And many other's to help in learning how linux works.What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'?
Understanding the Linux kernel source
What is the purpose of the lost+found folder in Linux and Unix?
When should I not kill -9 a process?
Any reason NOT to run Linux in a VM all the time?
What is the real difference between “apt-get” and “aptitude”? (How about “wajig”?)
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