man page sections

    The manual sections are traditionally defined as follows:

    1 Commands
    Those commands that can be executed by the user from
    within a shell.

    1P Posix Commands

    2 System calls
    Those functions which must be performed by the kernel.

    3 Library calls
    Most of the libc functions, such as qsort(3).

    3P Posix Functions

    4 Special files
    Files found in /dev.

    5 File formats and conventions
    The format for /etc/passwd and other human-readable
    files.

    6 Games

    7 Conventions and miscellaneous
    A description of the standard file system layout, net-
    work protocols, ASCII and other character codes, this
    man page, and other things.

    8 System management commands
    Commands like mount(8), many of which only root can
    execute.

    9 Kernel routines
    This is an obsolete manual section. Once it was
    thought a good idea to document the Linux kernel here,
    but in fact very little has been documented, and the
    documentation that exists is outdated already. There
    are better sources of information for kernel developers.