Read manual pages

Nobody remembers every option of every command. Experienced administrators look things up constantly, and the first place they look is the system itself. Every package installs manual pages, man pages for short, that describe its commands and files, written for exactly the version installed.

Open a manual page, and pick the right section when a name means two things.
Move around a page and search inside it.
Read a SYNOPSIS line: what to type literally, what to replace, what is optional and what may repeat.

Open a manual page

man followed by a name opens its manual page:

[student@workstation ~]$ man ls

LS(1)                            User Commands                           LS(1)

NAME
       ls - list directory contents

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

DESCRIPTION
       List  information  about  the FILEs (the current directory by default).
       Sort entries alphabetically if none of -cftuvSUX nor --sort  is  speci‐
       fied.
...

The page opens in less, so the keys you learnt in chapter 2 work here:

Key	Does
Space / b	Next / previous screen
d / u	Down / up half a screen
↓ / ↑	One line
/`text` Enter	Search forward; n next match, N previous
g / G	Start / end of the page
q	Quit

The parts of a page

Pages follow the same layout, though few use every heading:

Heading	What you find there
NAME	The name and a one-line description
SYNOPSIS	How to call it: the command line's shape
DESCRIPTION	What it does, and usually the options
OPTIONS	The options, when not in DESCRIPTION
EXAMPLES	Worked examples: often the fastest way to the answer
FILES	Files it reads or writes, such as configuration files
SEE ALSO	Related pages, with their section numbers

Sections: one name, several pages

The manual is divided into numbered sections. The ones an administrator uses most are 1, 5 and 8:

Section	Holds	Example
1	Commands any user runs	`ls(1)`, `passwd(1)`
2	System calls (for programmers)	`open(2)`
3	Library functions (for programmers)	`printf(3)`
4	Special files, mostly devices	`null(4)`
5	File formats and configuration files	`passwd(5)`, `fstab(5)`
7	Overviews, conventions, standards	`regex(7)`, `hier(7)`
8	Administration commands, usually for root	`useradd(8)`, `mount(8)`

That is why pages are written as passwd(5): the name plus the section. passwd(1) is the command that changes passwords; passwd(5) describes the /etc/passwd file. man passwd opens the first match, section 1. Put the section number first to choose:

[student@workstation ~]$ man 5 passwd

passwd(5)                     File Formats Manual                    passwd(5)

NAME
       passwd - password file

DESCRIPTION
       The  /etc/passwd file is a text file that describes user login accounts
...
       Each line of the file describes  a  single  user,  and  contains  seven
       colon-separated fields:

           name:password:UID:GID:GECOS:directory:shell

whatis lists every page with a name, one line each, so you can see which sections exist:

[student@workstation ~]$ whatis passwd
passwd (5)           - password file
passwd (1ossl)       - OpenSSL application commands
passwd (1)           - update user's authentication tokens

1ossl is a sub-section that OpenSSL uses for its own commands.

Read a SYNOPSIS line

The SYNOPSIS uses a small set of conventions to say what you may type. Select each part of these two real examples:

Reading a SYNOPSIS line: Select a convention below to highlight where it appears in the two command lines.

Notation	Means
bold or plain word	Type it exactly as shown
underlined or CAPITALS	Replace with your own value: a file name, a user name
`[ ]`	Optional
`...`	May be repeated
`{a\|b}` or `a\|b`	Choose exactly one

Some commands have several SYNOPSIS lines: each is a different way to call them. cp can copy one file to a new name, or several files into a directory:

SYNOPSIS
       cp [OPTION]... [-T] SOURCE DEST
       cp [OPTION]... SOURCE... DIRECTORY
       cp [OPTION]... -t DIRECTORY SOURCE...

Check your understanding

Which command shows the manual page that describes the /etc/passwd file?
Which manual section holds administration commands such as useradd and mount?
You are reading a man page. How do you find the next place the word recursive appears?
A SYNOPSIS reads: useradd [options] LOGIN. Which command fits it?
What does the ... after SOURCE in cp [OPTION]... SOURCE... DIRECTORY mean?
Which heading of a man page usually gets you to a working command fastest?