Vim for system administration (certification)

You regularly edit configuration files on Linux servers, /etc/ssh/sshd_config, /etc/fstab, /etc/nginx/nginx.conf, and you want to gain speed and precision. Vim (Vi IMproved) is found on almost every server, at least as a reduced version started by the vi command, and it is one of the skills expected for the LFCS and RHCSA certifications. This guide takes you from opening a file to mass substitution, with a minimal .vimrc suited to administration. The advanced features (splits, macros, plugins) are covered in the advanced Vim guide.

What you will learn

• Understand Vim's 3 modes, normal, insert, command, and avoid the classic mistakes
• Open, edit, save and quit a file cleanly
• Move efficiently with hjkl, words, lines, start and end of file
• Edit with operators and motions (dd, dw, yy, ciw, di"), Vim's "language"
• Search and substitute in a file or over a range of lines
• Set up a minimal .vimrc suited to administration

In which context?

On a Linux server, you often have no choice: the editor available over SSH is Vim (or vi, which is actually Vim on most modern distributions). Knowing how to use it efficiently avoids costly mistakes: a badly saved sshd_config file can lock you out of the server.

Real situation	Useful Vim skill
Fix a directive in /etc/nginx/nginx.conf	/pattern navigation, ciw editing
Comment out 10 lines of /etc/fstab for a test	Visual block mode Ctrl+v
Replace every occurrence of a port in a file	:%s/8080/9090/g
Add an option at the end of each configuration line	Substitution with $
Edit a CSV list copied into a temporary file	Text objects ci", di,

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Certification skill, RHCSA "Create and edit text files"

The RHCSA objectives (EX200) explicitly list "Create and edit text files". The current LFCS objectives no longer name vi, but its hands-on exams take place in a terminal, where every configuration fix goes through an editor. In both cases, what is tested is your ability to edit without mistakes under pressure: practise this guide until the commands become automatic.

Prerequisites: knowing the basics of vi (the 3 modes, hjkl, :w, :q) helps a lot. If these notions mean nothing to you, start with the vi guide: 15 minutes are enough to acquire these reflexes.

Vim's 3 modes

The first thing that puzzles people with Vim is that it works in modes. In a classic editor, you type and the text is added. In Vim, keys mean different things depending on the active mode. Understanding this mechanism is the key to never feeling lost again.

Mode	How to enter it	What it lets you do
Normal	Esc (default mode at start)	Move, delete, copy, paste, repeat
Insert	i, a, o, I, A, O from normal	Type text as in a classic editor
Command	: from normal	Save, quit, substitute, open another file

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A reflex to acquire

When in doubt, press Esc. You always go back to normal mode, from which you can choose what to do next. It is your resting position.

Enter insert mode

Several keys switch to insert mode, each with a useful nuance:

Key	Where does it insert?
i	Before the cursor
a	After the cursor
I	At the start of the current line
A	At the end of the current line
o	On a new line below
O	On a new line above

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Picking the right key saves time. If you want to add something at the end of a line, no need to go all the way with the arrows and then type a: A puts you there directly in insert mode.

Open, save, quit

This is the first thing to master: do not lose your work and do not get stuck in the editor.

Command	What it does
vim file	Opens (or creates) the file
:w	Saves (write)
:q	Quits, refuses if changes are unsaved
:wq or ZZ	Saves and quits
:q!	Quits without saving (discards the changes)
:w file	Saves under another name
:e file	Opens another file in the current session

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Editing a system file

To modify a file owned by root such as /etc/ssh/sshd_config, start Vim with sudo:

sudo vim /etc/ssh/sshd_config

If you forgot sudo and :w fails with E45: 'readonly' option is set, save with :w !sudo tee % then :q! to leave without overwriting with the in-memory version.

Move around a file

In normal mode, keys become movement commands. Forget the keyboard arrows: hjkl are faster because your hands stay on the home row.

Shortcut	Movement
h / j / k / l	Left / Down / Up / Right
w	Start of the next word
b	Start of the previous word
e	End of the current word
0	Start of the line
^	First non-blank character of the line
$	End of the line
gg	First line of the file
G	Last line of the file
25G or :25	Go to line 25
Ctrl+d / Ctrl+u	Half a page down / up
%	Matching parenthesis/brace

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The count

You can prefix any command with a number to repeat it: 5j moves down 5 lines, 3w moves 3 words forward, 2dd deletes 2 lines. It is like saying "do this N times".

Edit: operators and motions

Vim works like a language with verbs (operators) and objects (motions). Understanding this logic avoids memorising dozens of separate shortcuts.

The verbs (operators)

An operator does nothing on its own: it waits for a complement that tells it what to act on. Remember these four first, they cover most of the editing of a configuration file. The most useful day to day is c (change), because it chains deletion and switching to insert mode in one keystroke.

Operator	Verb	What it does
d	delete	Deletes
c	change	Deletes and switches to insert mode
y	yank	Copies into Vim's clipboard
> / <	indent	Shifts right / left

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Combine verb and motion

Vim's magic: everything composes. A few examples useful day to day:

Command	Reading	Result
dw	delete word	Deletes up to the next word
d$	delete to end of line	Deletes everything to the end
dd	delete line	Deletes the whole line
5dd	delete 5 lines	Deletes 5 lines
yy	yank line	Copies the line
cw	change word	Deletes the word and switches to insert mode
c$	change to end of line	Replaces the end of the line

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Copy, paste, undo

Command	What it does
yy	Copy the current line
p	Paste after the cursor (or after the line)
P	Paste before the cursor
x	Delete the character under the cursor
r{c}	Replace the character with {c} without entering insert mode
u	Undo the last change
Ctrl+r	Redo (the opposite of u)
.	Repeat the last change

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The `.` command, productivity gain #1

The dot . repeats the last change. If you just did ciw to change a word into nginx, move to another word and type . to replace it with nginx too. With n (next match) then . (repeat), you go through a file fixing each targeted occurrence, more precisely than a global substitution.

Text objects: act on logical structures

Text objects make Vim particularly powerful on configuration files. Instead of aiming at a position, you aim at a structure: the content between quotes, between parentheses, a whole word.

Syntax: operator + i or a + delimiter.

• i = inner (content without the delimiters)
• a = around (content + delimiters)

Take a line of /etc/nginx/nginx.conf:

listen 80 default_server;

Cursor on 80, you type:

Command	Result
ciw	Deletes 80 and switches to insert mode, type 443, Esc → listen 443 default_server;
daw	Deletes 80 (word + space)
C (capital)	Deletes from the position to the end of the line and switches to insert mode

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For a JSON file { "port": "8080", "host": "localhost" }, cursor on 8080:

Command	Result
ci"	Replaces the content between quotes ("8080" → "" + insert mode)
di"	Deletes only 8080
da"	Deletes "8080" (quotes included)

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The most useful delimiters:

Delimiter	Target
", ', `	Content between quotes
( or )	Content between parentheses
{ or }	Content between braces
[ or ]	Content between brackets
w	The word under the cursor
p	The current paragraph

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Visual mode: select before acting

Visual mode adds a reassuring selection step: you see what will be affected before acting.

Shortcut	Kind of selection
v	Character by character
V	Whole line
Ctrl+v	Rectangular block (columns)

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Once selected, press an action: y (copy), d (cut), c (replace), > (indent), < (unindent), Esc (cancel the selection).

Practical example: comment out 5 configuration lines

Scenario: disable 5 lines in /etc/fstab by adding # at the start of each.

1. Put the cursor on the first line to comment out.

2. Press Ctrl+v to enter visual block mode. -- VISUAL BLOCK -- appears at the bottom.

3. Move down with 4j to select 5 lines (current line + 4 below).

4. Press I (capital). Vim switches to insert mode at the start of the first line.

5. Type # (hash + space).

6. Press Esc. The # is applied automatically at the start of the 5 lines.

To uncomment: Ctrl+v, select the # column over the 5 lines with 4j then l, press d.

Search and substitute

In a 200-line configuration file, finding a parameter or renaming a value everywhere without mistakes is essential.

Search

Search is your fastest way to reach a directive in a 200-line file. Two reflexes to acquire: /pattern then n to go through the occurrences downwards, and * when the cursor is already on the word you are looking for, which saves typing it again.

Command	What it does
/pattern	Searches pattern downwards
?pattern	Searches pattern upwards
n	Next occurrence
N	Previous occurrence
*	Searches the word under the cursor (downwards)
#	Searches the word under the cursor (upwards)

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Substitute

The syntax is close to sed:

:[range]s/old/new/[flags]

Command	What it does
:s/foo/bar/	Replaces the first occurrence on the current line
:s/foo/bar/g	Replaces all occurrences on the line
:%s/foo/bar/g	Replaces all occurrences in the whole file
:%s/foo/bar/gc	Same with confirmation for each occurrence
:5,20s/foo/bar/g	Replaces between lines 5 and 20 only

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The % means "the whole file"

The % symbol in :%s/... means "from the first to the last line". Without the %, the substitution only applies to the current line. Forgetting the % is the most frequent beginner's mistake.

Example: rename a port in a configuration file

You have a file where listen 8080 appears 4 times. To switch everything to 9090 with confirmation:

:%s/8080/9090/gc

Vim highlights each occurrence and asks you y (yes), n (no), a (all), q (quit), l (this one then quit).

A minimal .vimrc for administration

The ~/.vimrc file is read when Vim starts. Here is a minimal configuration, enough for most administration tasks and in line with what certifications expect:

" === Appearance ===
syntax on               " Syntax highlighting
set number              " Line numbers
set showmatch           " Highlights the matching parenthesis

" === Search ===
set incsearch           " Results as you type
set hlsearch            " Highlights all occurrences
set ignorecase          " Case-insensitive
set smartcase           " Unless the search has a capital

" === Indentation ===
set tabstop=4
set shiftwidth=4
set expandtab           " Tab inserts spaces (not \t)
set autoindent          " Keeps the indentation

" === Comfort ===
set encoding=utf-8
set scrolloff=8         " Keeps 8 lines visible around the cursor

Create (or complete) ~/.vimrc:

vim ~/.vimrc

After changing it, apply it without restarting:

:source ~/.vimrc

Practise with vimtutor

Vim ships a 30-minute interactive tutorial that anchors the essential reflexes. Start it from the terminal:

vimtutor

It is the best investment to prepare for the LFCS and RHCSA exams.

Built-in help

Vim has very complete built-in documentation. Get into the habit of reading it directly.

Command	What it shows
:help	Help home page
:help motion	Everything about motions
:help text-objects	Everything about text objects
:help :substitute	About substitution
:helpgrep pattern	Searches the whole documentation

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In the help: Ctrl+] follows a link, Ctrl+o goes back, :q closes.

Troubleshooting

Most blockages with Vim come from a misidentified mode or from a file opened without the necessary permissions. Before looking further, press Esc to go back to normal mode: that alone solves half the situations in the table below.

Symptom	Likely cause	Solution
Strange characters as you type	You left insert mode without knowing it	Esc then i to resume
E45: 'readonly' option is set on :w	System file opened without sudo	:w !sudo tee % then :q!
Pasted text is indented in a staircase	Terminal without "bracketed paste": Vim applies auto-indentation to each pasted line	:set paste, paste, :set nopaste
No syntax highlighting	syntax on missing from .vimrc	Add syntax on
System copy-paste does not work	Vim without +clipboard	sudo apt install vim-gtk3 on Debian/Ubuntu
Odd characters in the terminal	Wrong encoding	set encoding=utf-8 in .vimrc
"The whole screen is selected"	You are in visual mode	Esc
Vim refuses to quit	Unsaved changes	:w to save or :q! to discard

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Key points

• Vim has 3 modes, normal, insert, command. When in doubt, Esc always takes you back to normal mode.
• Operators + motions form a language: d + w = delete word. Understand the logic and you will no longer have to memorise each shortcut separately.
• Text objects (ciw, ci", di() are the most useful on configuration files: they act on logical structures.
• The . command repeats the last change: combined with n after a search, it lets you fix each occurrence selectively.
• To substitute everywhere: :%s/old/new/gc, always add the % for the whole file and the c to confirm before each risky replacement.
• To edit a system file, open it with sudo vim. If you forgot: :w !sudo tee % saves the day.
• A minimal .vimrc (line numbers, highlighting, indentation, search) is enough for administration; the full configuration with plugins and macros belongs to the advanced Vim guide.
• Practise with vimtutor: 30 minutes that pay off in the timed LFCS and RHCSA exams.

Knowledge check

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Knowledge check

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• The timer starts when you click Start
• Multiple choice, true/false and short answer questions
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