Finding Documentation

Documentation Sources

Documentation sources

Linux documentation exists at multiple levels. When you don’t know how to use something, check these in order:

man pages - in-depth reference for commands, config files, syscalls, library functions
--help / -h - quick summary, always at your fingertips
help - for bash built-in commands (cd, echo, read, etc.)
GNU Info - hyperlinked, comprehensive documentation; often more thorough than man
/usr/share/doc/ - package-specific documentation installed alongside software
Online resources - distro wikis, official docs, community forums

`man` Pages

The man (manual) pages are the most-used Linux documentation source. They are present on every Linux system, and cover:

Programs and shell commands
System calls (kernel APIs)
Library functions
Configuration file formats (/etc/passwd, /etc/fstab)
Special files and devices

The man pages infrastructure dates to the early UNIX versions of the 1970s. They are formatted text, pipe through less for paging, and support search.

man ls                # open the ls manual page
man 8 useradd         # section 8 (admin commands) specifically
man -a socket         # show all pages named 'socket' across all sections

# Equivalent pairs:
man -f sysctl         # = whatis sysctl → list sections available
man -k sysctl         # = apropos sysctl → search all pages for keyword
man -w ls             # show path to the man page file

Man Page Sections

Section	Contents
1	Executable programs and shell commands
2	System calls (kernel-provided functions)
3	Library calls (within program libraries)
4	Special files (usually in `/dev`)
5	File formats and conventions (e.g., `/etc/passwd`)
6	Games
7	Miscellaneous (macro packages, conventions)
8	System administration commands (typically root only)
9	Kernel routines (non-standard)

Some sections have a letter suffix - for example, chapter 3X covers X Window API functions.

# intro pages exist in every section:
man -f intro
# intro (1)  - introduction to user commands
# intro (2)  - introduction to system calls
# ...

man 1 intro    # user commands intro
man 5 intro    # file formats intro

Searching Man Pages

man -k password        # all pages mentioning "password" = apropos password
man -k "^ls"           # pages whose name starts with ls (regex)

`whatis` and `apropos`

whatis ls
# ls (1)  - list directory contents

whatis sysctl
# sysctl (2)  - read/write system parameters
# sysctl (8)  - configure kernel parameters at runtime

apropos sysctl
# proc (5)    - process information, system information...
# sysctl (2)  - read/write system parameters
# sysctl (8)  - configure kernel parameters at runtime
# sysctl.d (5) - Configure kernel parameters at boot

`--help` and the `help` Built-in

`--help`

Most commands support --help (or -h) for a brief usage summary. This is faster than opening a full man page when you just need a syntax reminder:

man --help
tar --help | less
grep --help

`help` (bash built-ins)

When run inside a bash shell, commands like echo and cd are actually bash built-in versions - more efficient than the external binaries under /bin because they require fewer resources and no subprocess fork.

To get documentation for these built-ins:

help              # list all bash built-ins
help cd           # usage for the cd built-in
help echo         # usage for the echo built-in
help read         # usage for the read built-in

For built-ins, help does what -h does for standalone programs.

GNU Info

The GNU Info system is the GNU Project’s standard documentation format. It’s an alternative to man and preferred by GNU projects. Info pages:

Are free-form (not divided into fixed sections like man pages)
Support linked subsections (nodes) - similar in concept to hyperlinks
Are often more comprehensive and tutorial-like than man pages

info                    # browse the index of all topics
info ls                 # Info page for ls
info coreutils          # full GNU coreutils documentation
info bash               # very detailed bash reference

Navigating Info Pages

Each topic in info is called a node. Nodes are sections and subsections of the documentation. Items that act as links are marked with * at the start of their name (in menus) or :: at the end (inline references).

Key	Function
`n`	Go to next node
`p`	Go to previous node
`u`	Move up one level in the index
`Enter`	Follow a menu link
`q`	Quit
`h`	Help (key reference)
`s`	Search within info

Package Documentation

Software installed via your package manager often ships with additional documentation under /usr/share/doc/:

ls /usr/share/doc/                    # all packages' doc directories
ls /usr/share/doc/openssh-client/     # example: openssh docs
less /usr/share/doc/bash/README

Content varies by package - may include README files, changelogs, example configs, and upstream documentation.

Graphical Help Systems

Desktop environments also include graphical help browsers:

Desktop	Tool
GNOME	`gnome-help` (Yelp)
KDE	`khelpcenter`

These typically contain custom desktop help plus graphically-rendered info and man pages.

Resource	URL
Arch Wiki (excellent for all distros)	wiki.archlinux.org
Ubuntu Documentation	help.ubuntu.com
RHEL Documentation	access.redhat.com/documentation
Gentoo Handbook	wiki.gentoo.org/wiki/Handbook
Linux man pages online	man7.org/linux/man-pages
TLDR pages (short examples)	tldr.sh