首次安装系统不会产生，需要经过一段时间才会产生。
whatis：查看命令是什么，显示所有的章节
生成数据库方法：6：makeis
7：mandb
whatis command = man -f command
whereis：查看命令路径，帮助文档
man命令的配置文件：
6----/etc/man.config
7----/etc/man_db.conf
MAN PATH /PATH/TO/SOMEWHERE: 指明man文件搜索位置
man -M /PATH/TO/SOMEWHERE COMMAND: 到指定位置下搜索COMMAND命令的手册页并显示
man [章节] keyword：查看man 手册
man –a keyword：列出所有帮助
[root@localhost ~]# man -k cd
tcdrain (3) - get and set terminal attributes, line control, get and set baud rate
nscd.conf (5) - name service cache daemon configuration file
cd (1) - bash built-in commands, see bash(1)
cd (1p) - change the working directory
cd-create-profile (1) - Color Manager Profile Creation Tool
cd-drive (1) - show CD-ROM drive characteristics
cd-fix-profile (1) - Color Manager Testing Tool
cd-info (1) - shows Information about a CD or CD-image
cd-it8 (1) - Color Manager Testing Tool
cd-paranoia (1) - 9.8 (Paranoia release III via libcdio) - an audio CD reading utility whic...
cd-read (1) - reads Information from a CD or CD-image
cdrecord (1) - write data to optical disk media
ldns_pkt_cd (3) - (unknown subject)
ldns_pkt_set_cd (3) - (unknown subject)
mcd (1) - change MSDOS directory
nscd (8) - name service cache daemon
perlebcdic (1) - Considerations for running Perl on EBCDIC platforms
pitchplay (1) - wrapper script to play audio tracks with cdda2wav with different pitches ...
readcd (1) - read or write data Compact Discs
readmult (1) - a multitrack wrapper for cdda2wav
rpcdebug (8) - set and clear NFS and RPC kernel debug flags
rsyncd.conf (5) - configuration file for rsync in daemon mode
tcdrain (3p) - wait for transmission of output
Unicode::UCD (3pm) - Unicode character database
utf8 (3pm) - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code
XkbAllocDeviceInfo (3) - Obtain an XkbDeviceInfoRec structure
XkbAllocDeviceLedInfo (3) - Obtain an XkbDeviceLedInfoRec structure
XwcDrawImageString (3) - draw image text using a single font set
XwcDrawString (3) - draw text using a single font set
XwcDrawText (3) - draw text using multiple font sets
使用whatis数据库
相当于whatis = man –f keyword
[root@localhost ~]# man -f cd
cd (1) - bash built-in commands, see bash(1)
cd (1p) - change the working directory
打印man帮助文件的路径：man –w [章节] keyword（whereis keyword）
[root@localhost ~]# man -w cd
/usr/share/man/man1/builtins.1.gz
搜索man手册：man -k keyword，列出所有匹配的页面
[root@localhost ~]# man -k cd
tcdrain (3) - get and set terminal attributes, line control, get and set baud rate
nscd.conf (5) - name service cache daemon configuration file
cd (1) - bash built-in commands, see bash(1)
cd (1p) - change the working directory
cd-create-profile (1) - Color Manager Profile Creation Tool
cd-drive (1) - show CD-ROM drive characteristics
cd-fix-profile (1) - Color Manager Testing Tool
cd-info (1) - shows Information about a CD or CD-image
cd-it8 (1) - Color Manager Testing Tool
cd-paranoia (1) - 9.8 (Paranoia release III via libcdio) - an audio CD reading utility whic...
cd-read (1) - reads Information from a CD or CD-image
cdrecord (1) - write data to optical disk media
ldns_pkt_cd (3) - (unknown subject)
ldns_pkt_set_cd (3) - (unknown subject)
mcd (1) - change MSDOS directory
nscd (8) - name service cache daemon
perlebcdic (1) - Considerations for running Perl on EBCDIC platforms
pitchplay (1) - wrapper script to play audio tracks with cdda2wav with different pitches ...
readcd (1) - read or write data Compact Discs
readmult (1) - a multitrack wrapper for cdda2wav
rpcdebug (8) - set and clear NFS and RPC kernel debug flags
rsyncd.conf (5) - configuration file for rsync in daemon mode
tcdrain (3p) - wait for transmission of output
Unicode::UCD (3pm) - Unicode character database
utf8 (3pm) - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code
XkbAllocDeviceInfo (3) - Obtain an XkbDeviceInfoRec structure
XkbAllocDeviceLedInfo (3) - Obtain an XkbDeviceLedInfoRec structure
XwcDrawImageString (3) - draw image text using a single font set
XwcDrawString (3) - draw text using a single font set
XwcDrawText (3) - draw text using multiple font sets