Man pages are the extensive documentation for various programs, commands, libraries in Unix and Unix-like operating systems. They are divided by type into sections.
|1||Executable programs or shell commands||intro(1)|
|2||System calls (functions provided by the kernel)||intro(2)|
|3||Library calls (functions within program libraries)||intro(3)|
|4||Special files (usually found in /dev)||intro(4)|
|5||File formats and conventions eg /etc/passwd||intro(5)|
|7||Miscellaneous (including macro packages and conventions)||intro(7)|
|8||System administration commands (usually only for root)||intro(8)|
|9||Kernel routines [Non standard]||intro(9)|
More information at man(1).