Good documentation is essential for any software, and this applies equally to Linux commands.

Many Linux distributions and open-source communities provide detailed documentation that can be easily accessed online.

This documentation offers thorough explanations, instructions, and insights into Linux commands, giving users the necessary tools to effectively understand and utilize command-line utilities.

However, there are times when a brief reference is sufficient for quickly completing a task. In such cases, we can rely on the built-in system documentation available through the “man” command.

The “man” command stands for “manual” and serves as an interface to access the system’s manual pages. These pages, commonly referred to as “man pages,” contain comprehensive documentation for specific commands.

For instance, man pages for commands like mkdir, rmdir, dd, and others offer in-depth details regarding their usage and features.

<code>$ man mkdir
$ man rmdir
$ man dd</code>

Understanding the “man” command is crucial for efficient terminal usage in Linux.

man Command Syntax

The man command follows a simple syntax:

<code>$ man [OPTIONS] ...   ...</code>

As with other Linux commands, square brackets ([]) denote optional arguments, while angular brackets () indicate required arguments.

Sections of the man Command

Besides shell commands, Linux also supports elements like system calls, library functions, and special files. To maintain order, these are grouped into sections.

Here's a quick overview of each section:

• Section 1 – Contains man pages for executable programs or shell commands. Examples: cut, gzip, uniq.
• Section 2 – Covers system calls used by the kernel. Common ones include open(), read(), write(), close(), lseek().
• Section 3 – Includes library functions provided by user-space libraries. For example, strlen() from string.h, fopen() from stdio.h.
• Section 4 – Documents special files found under /dev, such as /dev/null and /dev/full.
• Section 5 – Describes file formats and conventions like /etc/hosts and /etc/shadow.
• Section 6 – Features games-related man pages.
• Section 7 – Miscellaneous commands including man and groff.

In this beginner-friendly guide, we will explore the “man” command in depth using practical examples.

1. View Man Page of Linux Command

A primary use of the man command is to display system documentation. The argument should be the name of a program, utility, or function.

Let’s view the man page for the sleep command:

<code>$ man sleep</code>

The output provides detailed information about the sleep command. Press 'q' to exit and return to the terminal.

You may notice numbers in parentheses next to the command name at the top. These represent the man page section.

For instance, SLEEP(1) indicates section 1.

2. Navigate Through a Man Page

Man pages often contain extensive details—descriptions, options, exit codes, bugs, authors, etc.

Since all this data won’t fit in one window, the man command uses a pager utility called less.

Use these keys to navigate:

• Up arrow – Move up line by line.
• Down arrow – Move down line by line.
• f or space – Scroll forward one screen.
• b – Scroll backward one screen.
• /pattern – Search forward.
• ?pattern – Search backward.

3. View Man Page from a Specific Section

Some names appear in multiple sections. For example, chown exists as both a command and a system call. Similarly, sleep is a command and a library function.

By default, man shows the first match it finds. So man sleep usually displays section 1 even if a version exists in section 3.

To specify a section, use its number before the command:

<code>$ man 3 sleep</code>

The above command displays the man page from section 3.

4. View Man Page from All Sections

Previously, we saw how to view pages from a default or specific section. But sometimes you might not know where else the page appears.

Use the -a option to view all versions:

<code>$ man -a sleep</code>

Each page is displayed one at a time. Press 'q' to move to the next.

5. Search Sections Of Man Page

If you only want to know which sections contain a particular man page, use the -f option:

<code>$ man -f sleep</code>

The output lists entries from sections 1 and 3 along with short descriptions.

6. Search Man Pages by Keyword

To find man pages containing a keyword, use the -k option:

<code>$ man -k sleep</code>

7. Find Source Location of Man Page

Man pages are compressed text files. Use -w to show their file paths:

<code>$ man -a -w sleep

<strong>/usr/share/man/man1/sleep.1.gz
/usr/share/man/man3/sleep.3.gz</strong></code>

The output reveals that the man page for section 1 resides in /usr/share/man/man1, and section 3 in /usr/share/man/man3.

8. View Man Page in GNOME Help Browser

So far, we've viewed pages in the terminal. You can also use the yelp command to view them in the GNOME help browser:

<code>$ yelp man:sleep</code>

Note: This method requires access to the GNOME desktop environment.

9. View Man Page in Web Browser

Additionally, you can use the -H option to open a man page in a web browser like Firefox:

<code>$ man -Hfirefox sleep</code>

On some systems, you may encounter an error:

<code>man: command exited with status 3: (cd /tmp/hmanQf1PgM && /usr/lib/man-db/zsoelim) | (cd /tmp/hmanQf1PgM && /usr/lib/man-db/manconv -f UTF-8:ISO-8859-1 -t UTF-8//IGNORE) | (cd /tmp/hmanQf1PgM && preconv -e UTF-8) | (cd /tmp/hmanQf1PgM && tbl) | (cd /tmp/hmanQf1PgM && groff -mandoc -Thtml)</code>

Fix this by installing the groff package, a typesetting tool used for formatting documents.

Use one of the following commands based on your distribution:

<code>$ sudo apt install groff         [On <strong>Debian, Ubuntu and Mint</strong>]
$ sudo yum install groff         [On <strong>RHEL/CentOS/Fedora</strong> and <strong>Rocky/AlmaLinux</strong>]
$ sudo emerge -a sys-apps/groff  [On <strong>Gentoo Linux</strong>]
$ sudo apk add groff             [On <strong>Alpine Linux</strong>]
$ sudo pacman -S groff           [On <strong>Arch Linux</strong>]
$ sudo zypper install groff      [On <strong>OpenSUSE</strong>]    </code>

Conclusion

This guide has covered how to access Linux system documentation using the “man” command. We’ve explored displaying man pages via terminal and GUI tools.

Are there other ways you access Linux documentation? Share your thoughts in the comments below.

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