man

    man，显示联机手册条目.
    提供有关主题的参考信息，例如命令、子例程和文件。man 命令提供由名称指定的对命令的单行描述。man 命令也提供所有命令的信息，这些命令的描述包含用户指定的关键字集合。
man 命令格式化指定的手册页面集合。如果为 Section 参数指定一个段，那么 man 命令在手册页面的该段中搜索 Title 参数指定的标题。Section 参数的值可以是 1 到 8 的阿拉伯数字或字母。
1 标准命令
2 系统调用
3 库函数/子例程
4 特殊文件
5 文件格式，例如（# man 5 passwd），即可查看该文件中各个字段的含义
6 游戏
7 杂项
8 系统管理员可用的命令
9 内核/内部指令

man -h

[root@oracle manpages-zh-1.5]# man -h
Cannot open the message catalog "man" for locale "zh_CN.GB2312"
(NLSPATH="/usr/share/locale/%l/LC_MESSAGES/%N")

man, version 1.6f

usage: man [-adfhktwW] [section] [-M path] [-P pager] [-S list]
[-m system] [-p string] name ...

a : find all matching entries
c : do not use cat file
d : print gobs of debugging information
D : as for -d, but also display the pages
f : same as whatis(1)
h : print this help message
k : same as apropos(1)
K : search for a string in all pages
t : use troff to format pages for printing
w : print location of man page(s) that would be displayed
(if no name given: print directories that would be searched)
W : as for -w, but display filenames only

C file   : use `file' as configuration file
M path   : set search path for manual pages to `path'
P pager  : use program `pager' to display pages
S list   : colon separated section list
m system : search for alternate system's man pages
p string : string tells which preprocessors to run
e - [n]eqn(1)   p - pic(1)    t - tbl(1)
g - grap(1)     r - refer(1)  v - vgrind(1)

-a man内定在显示第一个找到的手册之后就会停止搜寻,使用此选项会强迫man显示所有符合name的线上手册，在显示屏上按q键跳转。
-w 不要真的显示线上手册,但显示线上手册的位置.如果没有指定引数则显示man所搜寻的目录列表
-f 全文件匹配，显示所有文条目
-k 关键字匹配

帮助页面
    输入man命令（# man passwd）转到帮助页面后：

[root@oracle manpages-zh-1.5]# man passwd
PASSWD(1)                       User utilities                       PASSWD(1)

NAME
passwd - update user’s authentication tokens

SYNOPSIS
passwd  [-k]  [-l]  [-u  [-f]] [-d] [-n mindays] [-x maxdays] [-w
warndays] [-i inactivedays] [-S] [--stdin] [username]

DESCRIPTION
The passwd  utility  is  used  to  update  user’s  authentication
token(s).

This  task is achieved through calls to the Linux-PAM and Libuser
API.  Essentially, it initializes itself as  a  "passwd"  service
with  Linux-PAM  and  utilizes  configured  password  modules  to
authenticate and then update a user’s password.

A simple entry in the global  Linux-PAM  configuration  file  for
this service would be:

#
# passwd service entry that does strength checking of
# a proposed password before updating it.
#
passwd password requisite pam_cracklib.so retry=3
passwd password required pam_unix.so use_authtok
#

Note, other module types are not required for this application to
function correctly.

OPTIONS
-k     The option -k, is used to indicate that the update  should
only be for expired authentication tokens (passwords); the
user wishes to keep their non-expired tokens as before.

-l     This option is used to lock the specified account  and  it
:

第一行左上角显示PASSWD(1)，在标准命令段1中的passwd帮助信息
最后一行左下角显示冒号(:)，在这里可输入命令帮助使用者更好地浏览帮助信息，首先输入h，获得如下帮助信息

SUMMARY OF LESS COMMANDS

Commands marked with * may be preceded by a number, N.
Notes in parentheses indicate the behavior if N is given.

h  H                 Display this help.
q  :q  Q  :Q  ZZ     Exit.
---------------------------------------------------------------------------

MOVING

e  ^E  j  ^N  CR  *  Forward  one line   (or N lines).
y  ^Y  k  ^K  ^P  *  Backward one line   (or N lines).
f  ^F  ^V  SPACE  *  Forward  one window (or N lines).
b  ^B  ESC-v      *  Backward one window (or N lines).
z                 *  Forward  one window (and set window to N).
w                 *  Backward one window (and set window to N).
ESC-SPACE         *  Forward  one window, but don't stop at end-of-file.
d  ^D             *  Forward  one half-window (and set half-window to N).
u  ^U             *  Backward one half-window (and set half-window to N).
ESC-)  RightArrow *  Left  one half screen width (or N positions).
ESC-(  LeftArrow  *  Right one half screen width (or N positions).
F                    Forward forever; like "tail -f".
r  ^R  ^L            Repaint screen.
R                    Repaint screen, discarding buffered input.
---------------------------------------------------
Default "window" is the screen height.
Default "half-window" is half of the screen height.
---------------------------------------------------------------------------

SEARCHING

/pattern          *  Search forward for (N-th) matching line.
?pattern          *  Search backward for (N-th) matching line.
n                 *  Repeat previous search (for N-th occurrence).
N                 *  Repeat previous search in reverse direction.
ESC-n             *  Repeat previous search, spanning files.

中文支持
   Linux自带的帮助文档尽管有多重语言，但支持中文的发行版少之又少。对于刚开始英语阅读能力一般的程序员，中文支持是有必要的。
1、下载man中文手册包

[root@localhost /]# wget

2、语言环境：设置为中文

[root@oracle ~]# echo $LANG
zh_CN.UTF-8
[root@oracle ~]# export LANG=zh_CN.GB2312
[root@oracle ~]# echo $LANG
zh_CN.GB2312

3、解压中文手册包到指定目录

[root@oracle ~]# mkdir -p /root/man/zh_CN
[root@oracle ~]# tar zxvf manpages-zh-1.5.tar.gz
[root@oracle ~]# cd manpages-zh-1.5
[root@oracle ~]# make
mkdir UTF-8
cp -r src/man* UTF-8/
[root@oracle ~]# cp -r UTF-8/* ~/man/zh_CN/

至此已经将中文手册包安装到自己创建的目录中了
4、测试中文手册包是否安装成功

[root@oracle manpages-zh-1.5]# man -w
/usr/local/share/man:/usr/share/man/overrides:/usr/share/man/zh_CN:/usr/share/man:/usr/local/java/man:/root/man/zh_CN:/root/man:/usr/man:/usr/local/man
[root@oracle manpages-zh-1.5]# man -aw passwd
/usr/share/man/man1/passwd.1.gz
/usr/share/man/man5/passwd.5.gz
/root/man/zh_CN/man5/passwd.5

# man 5 -a passwd
显示英文的，按q键切换到中文帮助。