In linux operation and maintenance process, able to skillfully use the help is very important. There are several ways to get help in the linux.
what is: the role is a brief description of the command function you want to see; just packed whatis command system is no need to wait for some time to generate. Can also perform makewhatis (centos6) / mandb (centos7 )
command to create a whatis database. what is the command and the command is equivalent to man -f
For internal commands can be used to help see the help, use a help command.
For Help external commands can also be used, use a command --help (or command -h)
external command man command may also be used, can be seen in more detail using the method Command man, man command usage command can be seen , but may also include a help manual to see many aspects of configuration files and other man to help distinguish between chapters, the same command could have explained in more sections, you can use the whatis command command to see where the command section. When the man command can specify chapter as man 5 passwd. In the help file you can type '/' and '?' Search up and down.
man -a passwd lists all help listed first listed after the previous chapters quit the next chapter
man -k passwd passwd with a list of all the keywords contents
can be entered in the help file '/' and '?' conduct Search up and down
there a help command is info, more like the site, there are links to different content can click
to CentOS can also be used to find help manual to use redhat