Demystifying The Numbers In Linux Man Pages

Linux man pages are divided into sections to categorize different types of documentation. The section number indicates what type of command, file, or concept the man page describes. Knowing the purpose of the sections helps understand why a particular topic has that section number assigned.

This article provides an overview of the common man page sections, how to navigate them by number, useful reference tables, and advanced lookup tools. With a grasp of the section system, you can more effectively find documentation on Linux systems.

Purpose of Man Page Sections

The section numbers allow the documentation to be categorized by topic in a logical fashion. Some key reasons the man page sections are valuable include:

Table of Contents

Group related information together – All user commands are in section 1 for example.
Avoid namespace collisions – Common command names like “printf” can exist in section 1 and section 3 without conflict.
Standardize the documentation structure across UNIX systems.
Serve as a clue about the nature of the documented topic when looking up unfamiliar commands.

So rather than an unstructured mass of documentation, the sections create an information hierarchy.

Overview of Common Man Page Sections

While there are 10 man page sections numbered 0 through 9, just a few sections make up most day-to-day uses of man pages on Linux. Here is a breakdown of the sections you will likely encounter most often:

User commands (section 1)

This section covers executable command-line programs and shell commands directly accessible to users. Some examples include common commands like ls, grep, sudo along with Unix command-line utilities and user tools like system monitoring tools.

System calls (section 2)

System calls form the interface between user-space processes and the Linux kernel. This section documents requests like open, read, write, and other operations programs can use to have the kernel perform tasks.

Library functions (section 3)

Section 3 contains documentation on library functions that programmers can utilize within their code for common programming tasks. It includes standard C libraries like libc along with other common libraries like zlib compression functions.

Special files (section 4)

This section covers file system nodes that represent hardware devices and specialized device files. For example, console terminals, audio devices, random number generators. Sections of the /dev directory with device driver interfaces appear here.

File formats (section 5)

Documentation on common file formats used by various programs and components make up section 5. For example, filesystem tables like fstab, passwd user account files, and configuration file formats.

Games (section 6)

Traditional console and text-based games have entries in section 6. This includes classics like Solitaire along with Linux mainstays such as Sudoku.

Overview and conventions (section 7)

Documentation covering Linux standards and conventions are grouped in this section. For example, filesystem hierarchy standards, command syntax standards, the Linux boot process, and other architecture overviews.

System administration (section 8)

Documentation aimed at sysadmins managing services, networks, storage, device drivers, and kernel configuration lives in section 8.

Navigating Man Pages by Section Number

By specifying the man page section number, you can jump directly to a section of interest without having to guess which one documentation appears in. The general format is:

man [section_number] [topic]

For example, to view documentation on the passwd file format in section 5, use:

man 5 passwd

Omitting the section number gives the first man page match, which may not be the desired information. So utilizing the section number directly gets you to relevant documentation faster.

Useful Reference Tables for Man Page Sections

Several man pages exist that provide tables summarizing the purpose of the sections and listing common topics within each one. These serve as quick references when trying to recall what lives in a given section.

Man pages that have overviews of sections include:

man 7 man-pages – Summary table of sections
man 1 intro – List of common section 1 commands
man 2 intro – List of common section 2 system calls
man 3 intro – List of common section 3 library calls

These intro man pages give a high level overview and are handy as a memory aid. They allow you to rapidly search the contents of a section for the topic you want to explore.

Advanced Lookup Tools for Exploring Unfamiliar Man Pages

When you encounter unfamiliar man page topics, several tools exist to help understand what information resides there:

apropos – Search man page descriptions and summaries.
whatis – Display one-line man page descriptions.
man -f – Search for man pages matching a keyword.
man -k – Search contents and descriptions of man pages.

Using sections combined with these utilities allows focused exploration drilling down to the actual documentation on what you want to learn about.

Conclusion: Leveraging Sections for More Effective Man Page Lookup

Understanding the categorization system for man pages accelerates finding relevant documentation on Linux. Keeping the purpose of the numbered sections in mind while browsing or searching man pages directly gets you to the information you want faster.

Now you know the common man page sections, how sections help avoid ambiguity and collisions, tricks utilizing section numbers for lookup, handy reference tables, and advanced tools.

So leverage the numeric prefixes to demystify man pages and unlock the immense amount of documentation on Linux!