Cisco ASA and PIX Firewall Handbook

You mentioned earlier that there were "literally thousands of commands" in Linux. Where can I learn about them all?

Because there are so many commands, so many different varieties of Linux operating systems, and because you can always customize your Linux installation, there is no "official" list of all of the thousands of Linux commands you might encounter in Linux.

Several books do a good job of listing many of them, however. One of the very best is Linux in a Nutshell, little more than a concise reference of thousands of Linux commands, published by O'Reilly and Associates.

I haven't ever created any files or directories in my home directory, yet files or directories are already there, according to the ls command. Why?

Various Linux applications create files and directories for you when you start them. Depending on the amount of work you had already done with your Fedora Core 4 system before you started this chapter, the files in your home directory might not exactly match those in the examples.

What happens when using mv or cp if a file already exists with the same name as the destination I've given to the shell in my argument?

If the destination file already exists when you use mv or cp, it is replaced by the new file. The existing file is deleted before the new file by the same name is created. You should therefore learn to be cautious when using mv or cp in day-to-day work.