The Linux command line allows your system to remember commands that you use—up to a limit set by your HISTSIZE variable. Since each user’s HISTSIZE is generally set to 1000, that means Linux can remember the last 1000 commands you entered and make it easy to reuse them without retyping them.
Unless you configure your history settings differently, all of your commands will be remembered. You can put some restrictions on that behavior if you like. For example, you might not want to save every command you use to read a man page or every time you type pwd to ask where you’re currently sitting in the file system. How to restrict the commands that are remembered and which are not is covered here.
Source:: Network World – Linux