How to find documentation within my own GNU / Linux system

Many of those new to the world GNU / Linux they are full of doubts and unable to find a quick answer to their concerns, sometimes they don't even have a connection through which to access a support forum and finally end up with the idea that Linux is very difficult for them.

Most of those who find themselves in this situation are unaware that our own system contains a good part of the answers to our initial concerns. There are essentially three sources of documentation in a system GNU / Linux: man pages, info pages and application manuals packaged in / usr / share / doc.

In this article we will detail each of these sources.

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Man pages

The manual pages or "man pages" are the classic forms of reference documentation in Linux and Unix. Ideally, you can search the man pages for help for any command, configuration file, or library routine.

In practice, Linux is free software, and some pages have not been written or show their age. However, man pages are the first place to look when you need help. To access the man pages, just type Mon followed by the topic to be investigated.

A paging will be started, so you will press q when I finish reading. For example, to find information about the command ls, I would write:

$ man ls

Knowing the parts of the man pages it can be helpful to quickly jump to the information you need, you will find the following sections on the man page (Box 1):

Table 1: Manual Pages

NAME	Command name and description
SYNOPSIS	How to use the command
DESCRIPTION	In-depth explanation of how the command works
EXAMPLES	Suggestions on how to use the command
SEE ALSO	Related topics (Usually in man pages)

Sections of the man pages

The files that comprise the man pages are stored in / usr / share / man (or in / usr / man on some old systems). Within that directory, you will find that the manual pages are organized into the following sections (Box 2).

Table 2: Sections of the manual pages

man1	User programs
man2	System calls
man3	Library functions
man4	Special files
man5	File format
man6	Games
man7	Miscellany

Multiple man pages

Some topics exist in more than one section. To demonstrate this, we are going to use the command whats, which shows all the man pages available for this topic:

$ what is printf

printf (1) - format and print data

printf (3) - formatted output conversion

In this case, man printf it would be on the page of section 1 (User programs). If we were to write a C program, we would be more interested in the page in section 3 (Library functions). You can call up a certain section of man pages by specifying it on the command line, so to ask for printf, we can write:

$man 3 printf

Finding the correct man page

Sometimes it is difficult to find a few man pages on a given topic. In that case, you could use man -k to find the NAME section of the man pages. Know that this is a substring search, so something like man -k ls would give you a lot of outputs, here is an example using a more specific word:

$ man -k whatis whatis (1) - prints manual page descriptions

All about apropos

The previous example brought us a few more points. First, the command about is exactly equivalent to man -k, (Actually, I'll give you a secret. When you run man -k actually run about behind the scenes).

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The MANPATH line of code

We now turn to the second type of documentation that we will find in our GNU / Linux system. By default, the man program looks for the man pages in / usr / share / man, / usr / local / man, / usr / X11R6 / man and possibly / opt / man. sometimes you can find what you need by adding an additional path to the search path. That being the case, just edit /etc/man.conf in a text editor and add a line like the following:

MANPATH / opt / man

From here on, any man page in the directory / opt / man will be found. Remember you need to run again makewhatis to add these new man pages to the database whats.

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GNU info

One of the shortcomings of manual pages is that they do not support hypertext so you cannot easily jump from one page to another. Friends of GNU recognize this flaw, so they invented another documentation format: "info" pages.

Many of the GNU programs come with extensive documentation in the info page format. You can start reading info pages with the command info:

In this way we will bring an index of all the info pages available in the system. You can move in them with the arrow keys, follow "links" (indicated with a star) using the Enter key and to exit by pressing q. The keys are based on Emacs, so it should be easy for you to navigate if you are familiar with that editor.

For more information with the use of info, read their info page. You should be able to navigate them using the keys mentioned above:

$ info info

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/ usr / share / doc

There is one last source that can help you within Linux system. Many programs come equipped with additional documentation in other formats: text, PDF, PostScript, HTML, to name a few.

Take a look at / usr / share / doc (/ usr / doc on old systems). You will find a long list of directories, each of which comes with the applications on your system. Searching through this documentation can often reveal something interesting, such as tutorials or additional technical documentation. A quick check reveals a ton of material available to read:

$ cd / usr / share / doc

$ find. -type f | wc -l

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In other articles we will refer to external sources of documentation such as The Linux Documentation Project (LDP), mailing lists and newsgroups.

Source: Article taken from GUTL and written by Maikel Llamaret Heredia. Links: https://blog.desdelinux.net, http://www.raybenjamin.com, http://forum.codecall.net, http://www.linfo.org,  http://www.esdebian.org