Lesson 5: Getting Help

Goal: Learn to find documentation and help for any Linux command — without leaving the terminal.

Table of Contents

1. Manual Pages — man
2. Quick Description — whatis
3. The --help Flag
4. Find Commands — which & whereis
5. Search Manuals — apropos
6. Info Pages — info
7. Exercises

Manual Pages — man

man (manual) is the most comprehensive help system in Linux. Almost every command has a manual page.

Open a manual page

man ls

Navigation (same as less)

Man page structure

NAME        — Command name and short description
SYNOPSIS    — How to use the command (syntax)
DESCRIPTION — Detailed explanation
OPTIONS     — All available flags
EXAMPLES    — Usage examples (not always present)
SEE ALSO    — Related commands

Reading the SYNOPSIS

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

• ls — the command
• [OPTION] — optional flags (square brackets = optional)
• ... — can be repeated
• [FILE] — optional file argument

Man page sections

There are 9 sections of manual pages:

Some names exist in multiple sections:

# passwd the command (section 1)
man 1 passwd

# passwd the file format (section 5)
man 5 passwd

Practical examples

man cp        # How to copy files
man chmod     # How to change permissions
man crontab   # How to schedule tasks
man ssh       # How to connect remotely

Quick Description — whatis

whatis gives a one-line description of a command.

whatis ls

Output:

ls (1) - list directory contents

whatis chmod cp mv rm

Output:

chmod (1) - change file mode bits
cp (1)    - copy files and directories
mv (1)    - move (rename) files
rm (1)    - remove files or directories

This is perfect when you know the command but forgot what it does.

The --help Flag

Almost every command supports --help for a quick reference.

ls --help
cp --help
mkdir --help

This is shorter than the full man page and shows the most common options.

Some commands use -h

tar -h
git commit -h

Find Commands — which & whereis

which — Where is the binary?

which shows the full path of a command's executable.

which python3

Output:

/usr/bin/python3

which ls
# Output: /usr/bin/ls

which nano
# Output: /usr/bin/nano

which node
# Output: /usr/local/bin/node

Check if a command exists

which docker
# If no output → docker is not installed

which nonexistent-command
# No output = not found

whereis — Find binary, source, and man pages

whereis ls

Output:

ls: /usr/bin/ls /usr/share/man/man1/ls.1.gz

whereis python3

Output:

python3: /usr/bin/python3 /usr/lib/python3 /usr/share/man/man1/python3.1.gz

whereis shows:

• The binary location
• The source files (if available)
• The man page location

Search Manuals — apropos

apropos searches all man page descriptions for a keyword. Use it when you don't know the command name.

apropos "copy files"

Output:

cp (1)    - copy files and directories
install (1) - copy files and set attributes

apropos disk

Output:

df (1)     - report file system disk space usage
du (1)     - estimate file space usage
fdisk (8)  - manipulate disk partition table

apropos "network interface"

Update the database

If apropos returns nothing, update the database:

sudo mandb

Info Pages — info

Some GNU programs have more detailed documentation in info format.

info coreutils
info grep

Navigation in info

For most daily use, man and --help are sufficient.

Exercises

Exercise 1: Explore man pages

# 1. Look up the tar command
man tar
# Find the flag for extracting files (hint: search for "extract")

# 2. Look up chmod
man chmod
# Find the section about octal notation

# 3. Quick lookup
whatis tar chmod grep find

Exercise 2: Find commands

# 1. Where is the bash binary?
which bash

# 2. Find everything related to python
whereis python3

# 3. Find commands related to "compress"
apropos compress

# 4. Find commands related to "network"
apropos network

Exercise 3: Self-help

# 1. Check the help for the 'find' command
find --help

# 2. Check the help for 'grep'
grep --help

# 3. What does 'tee' do?
whatis tee

# 4. Read the man page for a command you've never used
man xargs

Key Takeaways

• man command — full documentation (your primary resource)
• whatis command — one-line description
• command --help — quick reference of options
• which command — find where a command lives
• whereis command — find binary, source, and man pages
• apropos keyword — search for commands by description
• When in doubt: man is your best friend

Next Lesson: Lesson 6: Input & Output — echo →