linux下man使用

man man 得到man的使用，一共分为9类：

 The table below shows the section numbers of the manual followed by the types of pages they contain.

       1   Executable programs or shell commands

                          man 1 ls

       2   System calls (functions provided by the kernel)

               man 2 open 

       3   Library calls (functions within program libraries)

              man 3 fopen 

       4   Special files (usually found in /dev)

       5   File formats and conventions eg /etc/passwd

       6   Games

       7   Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)

       8   System administration commands (usually only for root)

       9   Kernel routines [Non standard]