LFCA 13 🐧 Getting Help — man, -help, info - KandZ

Linux has thousands of commands, each with dozens of options. Nobody memorizes them all. Instead, every Linux system ships with its own documentation — manual pages, --help output, and GNU Info files. Knowing how to find the answer is more valuable than memorizing flags. The LFCA exam expects you to know the three main help systems, how to use them, and how to read a man page. This chapter is about looking things up — the skill that turns “I don’t know this command” into “I can figure it out.”

Key point: There are three main sources of help on a Linux system: man (manual pages, the standard reference), --help (quick usage summary from the command itself), and info (GNU hypertext documentation). man is the primary tool — nearly every command has a man page. --help is fast for reminders. info is deeper, but not every program has it. Learn all three, but reach for man first.

Why help matters

Linux has commands, options, and conventions that no one memorizes completely.

The reality of Linux:

Hundreds of user commands in /usr/bin
Thousands of options across them
Different implementations with different flags
Documentation that’s authoritative for the exact version installed

Three problems help solves:

“What does this command do?” — Read the description
“What options does it take?” — Read the options section
“How do I use it for X?” — Read the examples, or search

Why built-in help is better than memory: Man pages are versioned with the software. They match what’s actually on your system. Online docs might be for a different version. When you need the exact syntax, the man page is authoritative.

Why built-in help is better than search engines: No internet required. Man pages are local. man ls works offline, on a server, in a container. It’s instant.

The three sources:

Source	Command	Depth	Speed
Man pages	`man CMD`	Thorough	Fast
`--help`	`CMD --help`	Summary	Instant
Info	`info CMD`	Deep	Slower

Why the exam tests this: It’s a practical skill. System administrators use help constantly. Knowing how to find the answer is expected, not optional.

Why “RTFM” is bad advice without the M: “Read the manual” is only useful if you can find and read it. The skill isn’t telling people to read the manual — it’s knowing which manual, how to navigate it, and how to search it. That’s what this chapter teaches.

`man` — the manual pages

man displays manual pages. It’s the primary reference for every command, file format, and system call.

$ man ls

This opens the man page for ls in a pager (usually less).

What man pages contain:

Section	Contents
NAME	Command name and one-line description
SYNOPSIS	Usage syntax
DESCRIPTION	What the command does
OPTIONS	Every flag explained
FILES	Files the command uses
EXAMPLES	Usage examples (not always present)
SEE ALSO	Related commands
AUTHOR	Who wrote it
BUGS	Known issues

Navigating a man page:

Key	Action
Space or Page Down	Next page
b or Page Up	Previous page
Enter	Next line
Up/Down arrows	Scroll lines
`/pattern`	Search forward
`?pattern`	Search backward
`n`	Next match
`N`	Previous match
`g`	Go to start
`G`	Go to end
`q`	Quit

Why the pager: Man pages are often longer than a screen. The pager (less by default) lets you scroll, search, and quit without losing content. It’s the same navigation as reading a large file.

Searching within a page:

/recursive

Search for “recursive”. Press n to jump to the next match. N goes back.

Reading the SYNOPSIS: The synopsis is a compact usage pattern.

$ man ls | head -20
NAME
       ls - list directory contents

SYNOPSIS
       ls [OPTION]... [FILE]...

Reading it:

[OPTION]... — zero or more options
[FILE]... — zero or more files
ls alone lists the current directory

Brackets mean optional. Ellipsis means repeatable. Bold means literal. Italic means replace with a value.

The convention:

Symbol	Meaning
`command`	Literal text
`[OPTION]`	Optional
`[OPTION]...`	Optional, repeatable
`<FILE>` or FILE	Replace with a value
`a	b`

Why the synopsis is dense: It packs the full usage into a few lines. Once you can read it, you know how to call any command.

Why man pages exist: They’re the Unix tradition — documentation shipped with the software. Before the web, they were the only reference. They remain the authoritative one because they match the installed version. Every serious Linux tool has a man page.

Man page sections

Man pages are organized into numbered sections, each covering a different kind of documentation.

Section	Contents
1	User commands
2	System calls
3	Library functions
4	Special files (devices)
5	File formats and conventions
6	Games
7	Miscellaneous (conventions, protocols)
8	System administration commands
9	Kernel routines

Common sections you’ll use:

1 — commands you type (ls, grep, cp)
5 — file formats (/etc/passwd, /etc/fstab)
8 — admin commands (mount, fdisk, systemctl)

Examples:

$ man 1 ls        # user command
$ man 5 passwd    # file format
$ man 8 mount     # admin command
$ man 3 printf    # C library function

Why sections matter: Some names exist in multiple sections. passwd is both a command (section 1) and a file format (section 5). printf is both a shell built-in (section 1) and a C function (section 3). Specifying the section gets you the right page.

What happens without a section:

$ man passwd

Shows the first match — usually section 1 (the command). If you want the file format, specify section 5.

Listing all sections for a name:

$ man -a printf

-a shows all pages for the name, one after another.

What’s on the system:

$ man -k .

Lists every man page. Or:

$ whatis ls
ls (1)  - list directory contents

whatis gives the short description from a man page.

Why numbered sections: They separate documentation by audience and purpose. A user reading man ls doesn’t care about the C source. A programmer reading man 3 printf wants the API. The sections keep each audience’s docs together.

Why section 5 exists: File formats need documentation too. /etc/passwd, /etc/fstab, /etc/hosts — each has a specific format. The man page for passwd in section 5 describes it. Section 5 is where you look when a config file’s syntax isn’t obvious.

Searching man pages

Two tools find the right man page: whatis and apropos.

whatis — quick description:

$ whatis ls
ls (1)  - list directory contents

$ whatis grep
grep (1)  - print lines that match patterns

Shows the one-line description from the man page.

apropos — keyword search:

$ apropos "list directory"
ls (1)  - list directory contents

$ apropos "copy"
cp (1)       - copy files and directories
cpio (1)     - copy files to and from archives
dd (1)       - convert and copy a file

Searches the NAME and description fields of all man pages for a keyword.

man -k — same as apropos:

$ man -k "directory"

man -k and apropos are equivalent. Both search the same database.

The whatis database: Both commands query a pre-built index. On some systems it must be built:

$ sudo mandb

mandb builds or updates the database. Without it, apropos finds nothing.

Refining a search:

$ apropos -e "exact phrase"
$ apropos ^log       # names starting with log
$ apropos log$       # names ending with log

apropos accepts a regex. Useful when the keyword is too broad.

Examples:

$ apropos "password"
passwd (1)           - change user password
passwd (5)           - the password file
shadow (5)           - shadowed password file
openssl-passwd (1)   - compute password hashes

$ apropos "network"
ip (8)     - show / manipulate routing, network devices
ss (8)     - another utility to investigate sockets
...

Why search matters: You often know what you want to do — “copy files”, “see network” — but not which command does it. apropos bridges from intent to command name.

When apropos finds nothing: The database isn’t built, or the keyword doesn’t appear in any description. Try man -k, or a different keyword. Run sudo mandb if the database seems stale.

Why apropos is underused: It’s the fastest way to answer “which command does X?” New users search the web; experienced users run apropos. The man page for the command you didn’t know you needed is one command away.

`--help` — quick usage

Most commands accept --help and print a usage summary. It’s faster than a man page and works even when man isn’t installed.

$ ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Mandatory arguments to long options are mandatory for short options too.
  -a, --all                  do not ignore entries starting with .
  -A, --almost-all           do not list implied . and ..
      --author               with -l, print the author of each file
  ...

Why --help is useful:

Instant — no pager, no scrolling
Compact — only the usage and options
Available — works even on minimal systems
Exact — matches the installed version

What --help includes:

Usage line
Short description
Option list with descriptions
Sometimes examples

What it doesn’t include:

Detailed explanation
File formats
Related commands
Examples (usually)

The difference from man:

Aspect	`--help`	`man`
Speed	Instant	Fast
Length	Summary	Detailed
Structure	Flat list	Sections
Searchable	Not usually	Yes (`/pattern`)
Includes synopsis	Short	Full
Available on all commands	Most GNU	Nearly all

Not all commands support --help: Some use -h, some use help, some have neither. The convention is --help for GNU tools, but not every tool follows it.

Common alternatives:

Command	Help form
GNU tools	`--help`
Many BSD tools	`-h` or none
Bash built-ins	`help CMD`
Some apps	`-?`

Bash built-ins:

$ help cd
cd: cd [-L|[-P [-e]] [-@]] [dir]
    Change the shell working directory.
    ...

help is the shell’s built-in for its own commands. man cd might show a different cd (the program, not the built-in).

Why --help matters for scripts: When you’re working on a minimal system, or when man pages aren’t installed, --help still works. It’s the bare minimum every command provides.

Why --help is a convention, not a rule: There’s no standard that requires --help. GNU tools follow it. Others may not. When it doesn’t work, try -h, help, or read the man page. The convention is widespread because it’s useful — but it’s still a convention.

`info` — GNU documentation

info reads GNU Info files — hypertext documentation with links, menus, and cross-references.

$ info ls

This opens the Info reader for ls if an Info file exists.

What Info is:

A documentation format
Hyperlinked like the web
Structured with menus
Deeper than man pages for GNU tools

Navigation:

Key	Action
Space	Next page
Backspace	Previous page
n	Next node
p	Previous node
u	Up to parent node
m	Follow menu item
f	Follow link
l	Go back
q	Quit

Structure: Info files are organized as a tree of nodes — a top node, chapters, sections, and leaves. Each node has links to related nodes.

What Info has that man doesn’t:

Longer, more detailed descriptions
Tutorials and examples
Cross-references between nodes
Multiple documents linked together

What Info doesn’t have:

Universal coverage — not every command has an Info file
Familiar navigation for people used to less
The simplicity of man

When to use info: When man isn’t enough and you need deeper documentation. GNU tools often have Info files; many non-GNU tools don’t.

The info command:

$ info              # top-level menu
$ info ls           # specific command
$ info coreutils    # a whole package

Why Info exists: The GNU project found man pages limiting. Info lets authors write longer, linked documentation. For tools like gcc, emacs, and coreutils, the Info files are the authoritative reference.

Reading Info in a pager:

$ info --output=- ls | less

--output=- writes to stdout instead of the interactive reader. Useful for piping.

Why Info is often ignored: The navigation is different from less. Man pages are simpler. Many users never need the extra depth. But for GNU tools, Info is where the complete documentation lives.

Why “info” and not “man2”: Man pages were designed before hypertext. Info was the GNU project’s answer — structured, linked, hierarchical documentation. It’s a different format with a different philosophy. Both exist; both are useful for different cases.

Reading a man page

A man page has a standard structure. Knowing the sections makes it fast to find what you need.

The typical layout:

NAME
       command - one-line description

SYNOPSIS
       command [OPTION]... [ARGUMENT]...

DESCRIPTION
       Detailed explanation of what the command does.

OPTIONS
       -a, --all      description
       -b, --binary   description
       ...

FILES
       /path/to/file    description

SEE ALSO
       related(1), other(8)

AUTHOR
       Who wrote it.

Fast reading strategy:

NAME — confirm you have the right page
SYNOPSIS — see the usage shape
OPTIONS — find the flag you need
EXAMPLES — if present, copy and adapt
SEE ALSO — related commands

Searching:

$ man ls
/recursive

Press /, type the term, press Enter. Press n for next match.

Reading a specific section:

$ man 5 fstab

Shows the file format documentation for /etc/fstab.

Saving a man page:

$ man ls > ls-manual.txt

Or:

$ man ls | col -b > ls-manual.txt

col -b strips backspace characters used for bold/underline in the terminal.

Printing a man page:

$ man ls | col -b | lpr

The MANPATH: The search path for man pages.

$ echo $MANPATH

Usually set to /usr/share/man:/usr/local/share/man. Each directory holds man pages organized by section:

/usr/share/man/man1/ls.1
/usr/share/man/man5/passwd.5
/usr/share/man/man8/mount.8

Why the section suffix: The file name ends with the section number. That’s how man finds the right page for a given section.

Common reading patterns:

Need	Action
Quick description	Read NAME
Usage syntax	Read SYNOPSIS
Specific flag	Search `/flag`
Examples	Jump to EXAMPLES
Related commands	Read SEE ALSO

Why the structure is consistent: Man pages use the same section headers everywhere. Once you know the structure, you know where to look on any page. Consistency is what makes them fast to read.

Why SYNOPSIS is the most valuable section: It’s the whole usage of the command in a few lines. For most tasks, reading it and the NAME is enough. The DESCRIPTION and OPTIONS fill in details, but the synopsis answers “how do I call this?”

A full example

Using help systems to learn an unfamiliar command.

# ============================================
# PART 1: I NEED A COMMAND THAT DOES SOMETHING
# ============================================

# Search for commands related to disk usage
apropos "disk usage"
# df (1)              - report file system disk space usage
# du (1)              - estimate file space usage
# du (1)              - estimate file space usage
# ...

# ============================================
# PART 2: GET QUICK INFO
# ============================================

whatis df
# df (1)              - report file system disk space usage

whatis du
# du (1)              - estimate file space usage

# ============================================
# PART 3: READ THE MAN PAGE
# ============================================

man du
# DU(1)                       User Commands                      DU(1)
#
# NAME
#        du - estimate file space usage
#
# SYNOPSIS
#        du [OPTION]... [FILE]...
#        du [OPTION]... --files0-from=F
#
# DESCRIPTION
#        Summarize disk usage of the set of FILEs, recursively for
#        directories.
#        ...

# Search within the man page
# Press / then type "human"
# -h, --human-readable
#        print sizes in human readable format (e.g., 1K 234M 2G)

# Press q to quit

# ============================================
# PART 4: TRY --help
# ============================================

du --help
# Usage: du [OPTION]... [FILE]...
#   or:  du [OPTION]... --files0-from=F
# Summarize disk usage of the set of FILEs, recursively for directories.
#
# Mandatory arguments to long options are mandatory for short options too.
#   -a, --all             write counts for all files, not just directories
#       --apparent-size   print apparent sizes, rather than disk usage
#   -h, --human-readable  print sizes in human readable format (e.g., 1K 234M 2G)
#   -s, --summarize       display only a total for each argument
#   ...

# ============================================
# PART 5: USE THE COMMAND
# ============================================

du -sh /var/log
# 2.1G    /var/log

du -sh /var/log/*
# 12M     /var/log/apt
# 500M    /var/log/journal
# ...

# ============================================
# PART 6: CHECK INFO FOR DEEPER DOCS
# ============================================

info du 2>/dev/null || echo "No info page"
# (opens Info if available)
# q to quit

# ============================================
# PART 7: SEARCH FOR MORE
# ============================================

apropos "human readable"
# du (1)       - estimate file space usage
# ls (1)       - list directory contents
# df (1)       - report file system disk space usage
# ...

# ============================================
# PART 8: LOOK UP A FILE FORMAT
# ============================================

man 5 fstab
# FSTAB(5)                  File Formats Manual                FSTAB(5)
#
# NAME
#        fstab - static information about the filesystems
#
# DESCRIPTION
#        The file fstab contains descriptive information about the
#        various file systems the system can mount.
#        ...

# ============================================
# PART 9: THE WHATIS DATABASE
# ============================================

# If apropos finds nothing, rebuild the database
sudo mandb

# Then retry
apropos "editor"
# nano (1)     - Nano's ANOther editor
# vi (1)       - the standard text editor
# vim (1)      - Vi IMproved, a programmer's text editor
# ...

# ============================================
# PART 10: BASH BUILT-IN HELP
# ============================================

help cd
# cd: cd [-L|[-P [-e]] [-@]] [dir]
#     Change the shell working directory.
#
#     Change the current directory to DIR. The default DIR is the value
#     of the HOME shell variable.
#     ...

# man cd might show a different cd
man cd
# CD(1)              User Commands              CD(1)
# (this is the program, not the built-in)

Every part demonstrates a different help tool. Together they cover finding, reading, and using documentation.

Why this session: It walks through the real workflow — discover a command with apropos, get a quick description with whatis, read the man page for details, use --help for a quick reminder, and reach for info when deeper docs exist. That’s the full toolkit.

Complete Example Session

# ============================================
# PART 1: WHAT DOES THIS COMMAND DO?
# ============================================

whatis grep
# [ grep (1)  - print lines that match patterns ]

man grep | head -20
# [ GREP(1)  General Commands Manual  GREP(1) ]
# [
# [ NAME
# [        grep, egrep, fgrep - print lines that match patterns
# [
# [ SYNOPSIS
# [        grep [OPTION...] PATTERNS [FILE...]
# [ ...

# ============================================
# PART 2: --help QUICK CHECK
# ============================================

grep --help | head -15
# [ Usage: grep [OPTION]... PATTERNS [FILE]... ]
# [ Search for PATTERNS in each FILE. ]
# [ ...
# [   -i, --ignore-case         ignore case distinctions ]
# [   -v, --invert-match        select non-matching lines ]

# ============================================
# PART 3: SEARCH IN MAN PAGE
# ============================================

man grep
# /recursive
# (search for "recursive" — found as -r)
# q to quit

# ============================================
# PART 4: APPROPOS
# ============================================

apropos "search text"
# [ grep (1)         - print lines that match patterns ]
# [ egrep (1)        - print lines that match patterns ]
# [ fgrep (1)        - print lines that match patterns ]
# [ agrep (1)        - search a file for a string or regular expression ]

# ============================================
# PART 5: MAN SECTIONS
# ============================================

man -k "password"
# [ passwd (1)          - change user password ]
# [ passwd (5)          - the password file ]
# [ shadow (5)          - shadowed password file ]

man 5 passwd | head -30
# [ PASSWD(5)  File Formats Manual  PASSWD(5) ]
# [
# [ NAME
# [        passwd - the password file
# [
# [ DESCRIPTION
# [        /etc/passwd contains one line for each user account
# [ ...

# ============================================
# PART 6: MAN SECTION 1 VS 8
# ============================================

whatis mount
# [ mount (8)  - mount a filesystem ]

man 8 mount | head -20
# [ MOUNT(8)  System Administration  MOUNT(8) ]
# [
# [ NAME
# [        mount - mount a filesystem
# ...

# ============================================
# PART 7: BASH BUILT-IN HELP
# ============================================

type cd
# [ cd is a shell builtin ]

help cd
# [ cd: cd [-L|[-P [-e]] [-@]] [dir] ]
# [     Change the shell working directory. ]
# [ ... ]

# ============================================
# PART 8: INFO
# ============================================

info coreutils 2>/dev/null || echo "info not available"
# (interactive Info reader opens)
# q to quit

# ============================================
# PART 9: REBUILD WHATIS DATABASE
# ============================================

sudo mandb
# [ ... rebuilding man-db ... ]

apropos "compression"
# [ gzip (1)       - compress or expand files ]
# [ tar (1)        - an archiving utility ]
# [ bzip2 (1)      - a block-sorting file compressor ]
# [ xz (1)         - Compress or decompress .xz and .lzma files ]

# ============================================
# PART 10: SAVE MAN PAGE
# ============================================

man ls | col -b > /tmp/ls-manual.txt
wc -l /tmp/ls-manual.txt
# [ (number of lines) ]

# ============================================
# PART 11: PATTERN SEARCH
# ============================================

man grep
# /--context
# n (next match)
# (see the -C option)

# q to quit

# ============================================
# PART 12: SUMMARY COMMANDS
# ============================================

whatis ls cp mv rm
# [ ls (1)  - list directory contents ]
# [ cp (1)  - copy files and directories ]
# [ mv (1)  - move (rename) files ]
# [ rm (1)  - remove files or directories ]

apropos "copy file"
# [ cp (1)       - copy files and directories ]
# [ install (1)  - copy files and set attributes ]
# [ scp (1)      - secure copy (remote file copy program) ]
# [ rsync (1)    - a fast, versatile, remote (and local) file-copying tool ]

Every part exercises a help tool. Together they cover the workflow of finding documentation.

Quick Reference

The Three Help Systems

Tool	Command	Purpose
Man	`man CMD`	Full reference
Help	`CMD --help`	Quick summary
Info	`info CMD`	Deep GNU docs

`man` Flags

Flag	Effect
`man CMD`	Open man page
`man N CMD`	Open section N
`man -k WORD`	Search descriptions
`man -a CMD`	All sections
`man -w CMD`	Show path to man page
`man -f CMD`	Same as `whatis`

Man Sections

Section	Contents
1	User commands
2	System calls
3	Library functions
4	Special files
5	File formats
6	Games
7	Miscellaneous
8	Admin commands
9	Kernel routines

Pager Navigation

Key	Action
Space	Next page
b	Previous page
Enter	Next line
`/pattern`	Search forward
`?pattern`	Search backward
`n`	Next match
`N`	Previous match
`g`	Top
`G`	Bottom
`q`	Quit

SYNOPSIS Symbols

Symbol	Meaning
`[ ]`	Optional
`...`	Repeatable
`a \| b`	Either
`bold`	Literal
`italic`	Replace

Man Page Sections

Section	Contains
NAME	Command + one-liner
SYNOPSIS	Usage
DESCRIPTION	What it does
OPTIONS	Flags
FILES	Files used
EXAMPLES	Usage
SEE ALSO	Related
AUTHOR	Who wrote it
BUGS	Known issues

Search Commands

Command	Purpose
`whatis CMD`	One-line description
`apropos WORD`	Search descriptions
`man -k WORD`	Same as apropos
`mandb`	Rebuild database

`--help` Options

Form	Works on
`CMD --help`	GNU tools
`CMD -h`	Many tools
`help CMD`	Bash built-ins
`CMD -?`	Some tools

`info` Navigation

Key	Action
Space	Next page
n	Next node
p	Previous node
u	Up to parent
m	Menu item
f	Follow link
l	Go back
q	Quit

Where Man Pages Live

Path	Section
`/usr/share/man/man1/`	User commands
`/usr/share/man/man5/`	File formats
`/usr/share/man/man8/`	Admin commands
`/usr/local/share/man/`	Local installs

Common Reading Patterns

Need	Action
What does it do?	Read NAME
How to use it?	Read SYNOPSIS
Specific flag?	Search `/flag`
Examples?	Jump to EXAMPLES
Related tools?	Read SEE ALSO

Same Name, Different Sections

Name	Section 1	Section 5
passwd	Command to change password	Password file format
fstab	—	Filesystem mount file
hosts	—	Hostname resolution file
printf	Shell built-in	—
mount	—	Admin command (section 8)

Save and Print

Task	Command
Save	`man CMD > file.txt`
Strip formatting	`man CMD \| col -b > file.txt`
Print	`man CMD \| col -b \| lpr`
Read in editor	`man CMD \| col -b \| vim -`

Environment Variables

Variable	Meaning
`$MANPATH`	Search path for man pages
`$PAGER`	Program used to display
`$LESS`	Options for `less`
`$MANWIDTH`	Line width for man output

When to Use Which

Situation	Use
Learning a new command	`man`
Quick reminder	`--help`
Finding a command	`apropos`
Identifying a command	`whatis`
Deep GNU docs	`info`
Bash built-in	`help`
File format	`man 5`
Admin command	`man 8`

Common Errors

Error	Cause	Fix
`No manual entry`	No man page	Try `--help`
`apropos: nothing appropriate`	DB not built	`sudo mandb`
`info: No menu item`	No Info file	Use `man`
Wrong section shown	Ambiguous name	Specify number
Garbled output	Terminal issues	`col -b`

What’s the Difference

Feature	`man`	`--help`	`info`
Depth	Deep	Summary	Deepest
Speed	Fast	Instant	Slower
Navigation	Pager	None	Info reader
Search	✅	❌	✅
Coverage	Universal	Most	GNU
Structure	Sections	Flat list	Hypertext

Best Practices

✅ Do This:

# Start with man for any unfamiliar command
man rsync                                         # ✅

# Use apropos when you don't know the command
apropos "copy files"                              # ✅

# Use whatis for a quick description
whatis tar                                        # ✅

# Use --help for a fast reminder
tar --help                                        # ✅

# Search inside a man page
man rsync
/recursive                                        # ✅

# Specify the section when needed
man 5 crontab                                     # ✅

# Use help for bash built-ins
help cd                                           # ✅

# Rebuild the whatis database if empty
sudo mandb                                        # ✅

# Read EXAMPLES if present
man rsync | grep -A20 EXAMPLES                    # ✅

# Save a man page
man iptables | col -b > iptables.txt              # ✅

❌ Don’t Do This:

# Don't guess flags
command -z  # what does -z do?                       # ⚠️

# Don't read the entire man page for one flag
man ls  # then scroll forever                        # ⚠️

# Don't ignore man sections
man passwd  # which passwd?                          # ⚠️

# Don't skip --help for a quick check
man verylongcommand  # use --help first              # ⚠️

# Don't forget bash has its own help
man cd  # shows the program, not the built-in        # ⚠️

# Don't parse man pages for options
man ls | grep --                            # ⚠️

# Don't assume info exists
info rm  # may not exist                             # ⚠️

# Don't ignore SEE ALSO
# It lists related commands you might need           # ⚠️

# Don't run apropos without building the database
apropos x  # may return nothing                       # ⚠️

Common Pitfalls

Pitfall	Problem	Solution
Wrong man section	Wrong page	Specify the number
Missing man page	No docs	Try `--help`
`apropos` finds nothing	DB not built	`sudo mandb`
Skipping SYNOPSIS	Missed usage	Read it first
Ignoring EXAMPLES	Reinventing	Read them
`man cd` shows program	Not built-in	Use `help cd`
Pager confusion	Can’t exit	Press `q`
Long output	Overwhelming	Search with `/`
No `--help`	Missing	Try `-h` or `man`
`info` not installed	No GNU docs	Use `man`

Real-World Examples

1. Read a command’s man page

man ls

2. Get a quick description

whatis grep

3. Search for a command

apropos "compress file"

4. Specific man section

man 5 passwd

5. Search within a man page

man tar
/human

6. Quick usage summary

tar --help

7. Bash built-in help

help cd

8. All man pages for a name

man -a printf

9. Rebuild man database

sudo mandb

10. Find man page path

man -w ls

11. Read Info docs

info coreutils

12. Save a man page

man iptables | col -b > rules-doc.txt

13. Find all commands in a section

man -s 1 -k . | wc -l

14. Check if man page exists

man -w nonexistent  # returns non-zero if missing

15. Search all sections

apropos "sockets"

16. Read file format docs

man 5 hosts

17. Read admin command docs

man 8 systemctl

18. Follow SEE ALSO

man grep
# SEE ALSO: egrep(1), fgrep(1), rgrep(1)

19. Browse man in an editor

man ls | col -b | vim -

20. Learn a command quickly

# NAME + SYNOPSIS + first of OPTIONS
man rsync | head -40

Visual: The Help Systems

┌──────────────────────────────────────────────┐
│  man                                         │
│  ─ Full reference                            │
│  ─ Sections                                  │
│  ─ Searchable                                │
│  ─ Universal coverage                        │
│                                              │
└──────────────────────────────────────────────┘

┌──────────────────────────────────────────────┐
│  --help                                      │
│  ─ Quick usage                               │
│  ─ Instant                                   │
│  ─ No pager                                  │
│  ─ Most GNU tools                            │
│                                              │
└──────────────────────────────────────────────┘

┌──────────────────────────────────────────────┐
│  info                                        │
│  ─ Hypertext                                 │
│  ─ Deepest docs                              │
│  ─ GNU tools                                 │
│  ─ Menu-based navigation                     │
│                                              │
└──────────────────────────────────────────────┘

Visual: man Page Structure

┌──────────────────────────────────────────────┐
│  NAME                                        │
│  ─ command - one line                        │
│                                              │
│  SYNOPSIS                                    │
│  ─ command [OPTIONS] [ARGS]                  │
│                                              │
│  DESCRIPTION                                 │
│  ─ detailed explanation                      │
│                                              │
│  OPTIONS                                     │
│  ─ flag     description                      │
│  ─ flag     description                      │
│                                              │
│  FILES                                       │
│  ─ /path     purpose                         │
│                                              │
│  SEE ALSO                                    │
│  ─ related(1), other(8)                      │
│                                              │
└──────────────────────────────────────────────┘

Visual: Man Sections

┌──────────────────────────────────────────────┐
│  1  User commands       ls, cp, grep         │
│  2  System calls        open, read, write    │
│  3  Library functions   printf, malloc       │
│  4  Special files       /dev/*               │
│  5  File formats        passwd, fstab        │
│  6  Games                                    │
│  7  Miscellaneous       conventions          │
│  8  Admin commands      mount, fdisk         │
│  9  Kernel routines                          │
│                                              │
│  Most common: 1, 5, 8                        │
│                                              │
└──────────────────────────────────────────────┘

Visual: SYNOPSIS Reading

┌──────────────────────────────────────────────┐
│  ls [OPTION]... [FILE]...                    │
│  ─┬ ────────┬─ ─────┬─                       │
│   │         │       │                        │
│   │         │       └ zero or more files     │
│   │         │                                │
│   │         └ zero or more options          │
│   │                                          │
│   └ command name                             │
│                                              │
│  [ ] = optional                              │
│  ... = repeatable                            │
│  | = either                                  │
│                                              │
└──────────────────────────────────────────────┘

┌──────────────────────────────────────────────┐
│  cp [OPTION]... SOURCE... DEST               │
│  ─┬ ────────┬─ ─────┬─ ─────                  │
│   │         │       │     │                  │
│   │         │       │     └ destination      │
│   │         │       └ one or more sources    │
│   │         └ options                        │
│   └ command                                  │
│                                              │
└──────────────────────────────────────────────┘

Visual: apropos Workflow

┌──────────────────────────────────────────────┐
│  "I want to copy files"                      │
│       │                                      │
│       ▼                                      │
│  apropos "copy"                              │
│       │                                      │
│       ▼                                      │
│  cp (1)      - copy files and directories    │
│  rsync (1)   - fast, versatile copy          │
│  scp (1)     - secure copy                   │
│  dd (1)      - convert and copy a file       │
│       │                                      │
│       ▼                                      │
│  man cp                                      │
│                                              │
└──────────────────────────────────────────────┘

Visual: Searching in man

┌──────────────────────────────────────────────┐
│  $ man tar                                   │
│                                              │
│  (inside pager)                              │
│  /human-readable                             │
│       │                                      │
│       ▼                                      │
│  [match highlighted]                         │
│                                              │
│  n → next match                              │
│  N → previous match                          │
│                                              │
│  q → quit                                    │
│                                              │
└──────────────────────────────────────────────┘

Visual: man vs –help vs info

┌──────────────────────────────────────────────┐
│  man CMD                                     │
│  ──────────────► detailed page               │
│  ──────────────► sections                    │
│  ──────────────► searchable                  │
│                                              │
│  CMD --help                                  │
│  ──────────────► quick summary               │
│  ──────────────► flat list                   │
│  ──────────────► instant                     │
│                                              │
│  info CMD                                    │
│  ──────────────► hypertext                   │
│  ──────────────► menus and links             │
│  ──────────────► deepest                     │
│                                              │
└──────────────────────────────────────────────┘

Visual: man Page Sources

┌──────────────────────────────────────────────┐
│  $ man -w ls                                 │
│  /usr/share/man/man1/ls.1.gz                 │
│                                              │
│  Path structure:                             │
│  /usr/share/man/                             │
│  └── man1/                                   │
│      └── ls.1.gz        ← compressed source  │
│                                              │
│  man decompresses and displays               │
│                                              │
└──────────────────────────────────────────────┘

Visual: When apropos Finds Nothing

┌──────────────────────────────────────────────┐
│  $ apropos "obscure thing"                   │
│  obscure thing: nothing appropriate          │
│                                              │
└──────────────────────────────────────────────┘
                  │
                  ▼
┌──────────────────────────────────────────────┐
│  Possible causes:                            │
│                                              │
│  1. Database not built                       │
│  2. Keyword not in any description           │
│  3. Man pages not installed                  │
│                                              │
└──────────────────────────────────────────────┘
                  │
                  ▼
┌──────────────────────────────────────────────┐
│  Fix:                                        │
│  $ sudo mandb                                │
│  (rebuilds the whatis database)              │
│                                              │
│  Then retry                                  │
│                                              │
└──────────────────────────────────────────────┘

Visual: Decision Flow

┌──────────────────────────────────────────────┐
│  Need to know which command does X?          │
│       └── apropos "X"                        │
│                                              │
│  Need one-line description?                  │
│       └── whatis CMD                         │
│                                              │
│  Need full docs?                             │
│       └── man CMD                            │
│                                              │
│  Need a quick reminder?                      │
│       └── CMD --help                         │
│                                              │
│  Need file format docs?                      │
│       └── man 5 FILE                         │
│                                              │
│  Need admin command docs?                    │
│       └── man 8 CMD                          │
│                                              │
│  Need bash built-in docs?                    │
│       └── help CMD                           │
│                                              │
│  Need GNU deep docs?                         │
│       └── info CMD                           │
│                                              │
└──────────────────────────────────────────────┘

Summary

Tool	Command	Purpose
`man`	`man CMD`	Manual pages — full reference
`man N`	`man 5 passwd`	Specific section
`apropos`	`apropos WORD`	Search descriptions
`whatis`	`whatis CMD`	One-line description
`--help`	`CMD --help`	Quick usage
`help`	`help CMD`	Bash built-ins
`info`	`info CMD`	GNU hypertext docs
`mandb`	`sudo mandb`	Rebuild whatis DB

Key takeaways:

man is the primary reference — nearly every command has a man page
Man pages are organized into sections — 1 for commands, 5 for file formats, 8 for admin
man 5 fstab — specify the section when the name is ambiguous
whatis CMD gives a one-line description
apropos WORD searches all man page descriptions for a keyword
man -k WORD is the same as apropos
sudo mandb rebuilds the search database if apropos finds nothing
CMD --help prints a quick usage summary — faster than a man page
help CMD is for bash built-ins — man cd shows a different program
info CMD opens GNU hypertext documentation — deeper than man
SYNOPSIS uses [ ] for optional, ... for repeatable, | for either
Pager keys — Space next, b previous, / search, n next match, q quit
man CMD | col -b > file saves a formatted man page
Man pages match the installed version — always accurate for your system

Remember: Nobody memorizes every command and flag. The skill is knowing how to find the answer. man is the reference — full, searchable, versioned. --help is the quick reminder. info is the deep dive. apropos bridges from intent to command. When you don’t know, look it up. That’s not a weakness — it’s the professional habit. The exam tests it because every Linux admin uses it daily.

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