Linux command man is one of the most useful command when you worked on Linux system. everybody know that man command can help you to print the help information of linux command. you maybe just know its simple usage. there are other usages of man command that you also should know. this post will show you how to deep understand linux man command.
Man command use to format and display the on-line manual pages, these manual information wrote by each command’s develper. and the manual include about 8 sections as below:
man1: User programs
Manual pages that describe publicly accessible commands are contained
in this chapter. Most program documentation that a user will need to
use is located here.
man2: System calls
This section describes all of the system calls (requests for the kernel
to perform operations).
man3: Library functions and subroutines
Section 3 describes program library routines that are not direct calls
to kernel services. This and chapter 2 are only really of interest to
programmers.
man4: Special files
Section 4 describes the special files, related driver functions, and
networking support available in the system. Typically, this includes
the device files found in /dev and the kernel interface to networking
protocol support.
man5: File formats
The formats for many data files are documented in the section 5. This
includes various include files, program output files, and system files.
man6: Games
This chapter documents games, demos, and generally trivial programs.
Different people have various notions about how essential this is.
man7: Miscellaneous Manual pages that are difficult to classify are
designated as being section 7. The troff and other text processing
macro packages are found here.
man8: System administration Programs used by system administrators
for system operation and maintenance are documented here. Some of
these programs are also occasionally useful for normal users.
When we view the manual guide of one command using “man” command, it mainly shown up the first (man 1)and the fifth (man 5) section part.
For example, “man ls” command same as “man 1 ls”, it will show “ls” command ‘s man 1 section information. you also can see the “LS(1)” string from manual page, the “1” indicated that “man ls” command will call “man 1 ls”.
All manual page are stored under “/usr/share/man” directory:
[root@osetc~]# ls -l /usr/share/man total 352 drwxr-xr-x. 5 root root 4096 Dec 17 2012 bg drwxr-xr-x. 5 root root 4096 Apr 3 2012 cs drwxr-xr-x. 5 root root 4096 Dec 17 2012 da drwxr-xr-x. 5 root root 4096 Apr 3 2012 de drwxr-xr-x. 5 root root 4096 Dec 17 2012 el drwxr-xr-x. 5 root root 4096 Dec 17 2012 en drwxr-xr-x. 5 root root 4096 Dec 17 2012 es drwxr-xr-x. 5 root root 4096 Dec 17 2012 fi drwxr-xr-x. 6 root root 4096 Apr 3 2012 fr drwxr-xr-x. 5 root root 4096 Dec 17 2012 hr drwxr-xr-x. 4 root root 4096 Dec 17 2012 hu drwxr-xr-x. 3 root root 4096 Dec 17 2012 id drwxr-xr-x. 6 root root 4096 Apr 3 2012 it drwxr-xr-x. 5 root root 4096 Apr 3 2012 ja drwxr-xr-x. 5 root root 4096 Dec 17 2012 ko drwxr-xr-x. 2 root root 4096 Sep 23 2011 man0p drwxr-xr-x. 2 root root 36864 May 12 2014 man1 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man1p drwxr-xr-x. 2 root root 4096 Sep 23 2011 man1x drwxr-xr-x. 2 root root 4096 Sep 23 2011 man2 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man2x drwxr-xr-x. 2 root root 110592 Apr 22 2014 man3 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man3p drwxr-xr-x. 2 root root 4096 Sep 23 2011 man3x drwxr-xr-x. 2 root root 4096 Dec 17 2012 man4 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man4x drwxr-xr-x. 2 root root 4096 Apr 22 2014 man5 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man5x drwxr-xr-x. 2 root root 4096 Sep 23 2011 man6 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man6x drwxr-xr-x. 2 root root 4096 Apr 22 2014 man7 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man7x drwxr-xr-x. 2 root root 20480 May 12 2014 man8 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man8x drwxr-xr-x. 2 root root 4096 Sep 23 2011 man9 drwxr-xr-x. 2 root root 4096 Sep 23 2011 man9x drwxr-xr-x. 2 root root 4096 Sep 23 2011 mann drwxr-xr-x. 5 root root 4096 Dec 17 2012 nl drwxr-xr-x. 5 root root 4096 Apr 3 2012 pl drwxr-xr-x. 5 root root 4096 Dec 17 2012 pt drwxr-xr-x. 5 root root 4096 Dec 17 2012 pt_BR drwxr-xr-x. 5 root root 4096 Dec 17 2012 ro drwxr-xr-x. 6 root root 4096 Dec 17 2012 ru drwxr-xr-x. 3 root root 4096 Dec 17 2012 sk drwxr-xr-x. 5 root root 4096 Dec 17 2012 sl drwxr-xr-x. 6 root root 4096 Dec 17 2012 sv drwxr-xr-x. 5 root root 4096 Dec 17 2012 tr drwxr-xr-x. 4 root root 4096 Dec 17 2012 zh_CN drwxr-xr-x. 4 root root 4096 Dec 17 2012 zh_TW
If you want to check which man section include for linux command, use “man” command with “-f” option, type:
[root@osetc man5]# man -f init init (5) - Upstart init daemon job configuration init (8) - Upstart process management daemon
Display all the manual pages that match command name, using “man -a” command, type:
[root@osetc man5]# man -a init
By default, man will exit after displaying the first manual page it find. Using the option “-a” forces man to display all the manual pages that match name, not just the first.