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Text Editors

vi is present on almost every Linux server, rescue shell and container base image, so a small set of vim keys is a baseline skill. nano is friendlier and is the default editor on Ubuntu.

Track: Core · Interview weight: Low

Must-Know Facts

Fact Value Verify with
vi on RHEL vim-minimal; full vim is vim-enhanced rpm -qf /usr/bin/vi
vi on Ubuntu Alternatives link to vim.basic or vim.tiny readlink -f /usr/bin/vi
Default editor on Ubuntu nano, through the editor alternative update-alternatives --display editor
Editor used by tools $VISUAL, then $EDITOR, then a built-in default echo $EDITOR
Edit a root file safely sudoedit <file> (sudo -e); runs the editor as the user sudoedit /etc/hosts
Learn vim vimtutor (30 minutes) vimtutor

Vim Survival Keys

vim is modal: Normal mode for commands, Insert mode for typing, Command-line mode after :. Esc always returns to Normal mode.

Keys Action
i, a, o Insert before cursor, after cursor, on a new line below
Esc Back to Normal mode
:w, :q, :wq or :x, :q! Save, quit, save and quit, quit without saving
h j k l, w, b Move by character or word
0, $, gg, G, :42 Line start, line end, file start, file end, line 42
dd, yy, p, P Delete (cut) line, copy line, paste after, paste before
x, u, Ctrl+R Delete character, undo, redo
/text, n, N Search forward, next, previous
:%s/old/new/g Replace in the whole file
:set number, :set list Line numbers; show tabs and line ends
v, V, Ctrl+V Select characters, lines, a block

Non-Interactive Edits

vim runs in Ex mode for scripted edits, which is useful where sed -i behaves differently between GNU and BSD:

printf 'listen 80\nserver_name old.example.com\n' > /tmp/site.conf
vim -Es -c '%s/old/new/g' -c 'wq' /tmp/site.conf
cat /tmp/site.conf

Output:

listen 80
server_name new.example.com

Choosing the Editor

On Ubuntu:

update-alternatives --display editor | head -3
readlink -f /usr/bin/vi

Output:

editor - auto mode
  link best version is /bin/nano
  link currently points to /bin/nano
/usr/bin/vim.basic

sudo update-alternatives --config editor changes the default for crontab -e and visudo. On RHEL, vi comes from vim-minimal and vim from vim-enhanced.

EDITOR and VISUAL choose the editor for other tools

Setting export EDITOR=vim VISUAL=vim in ~/.bashrc makes crontab -e, git commit, kubectl edit and systemctl edit use vim.

sudo vim gives the editor root privileges

From sudo vim, :!sh opens a root shell, which bypasses a sudoers rule meant to allow editing only. sudoedit copies the file, runs the editor as the user, and writes the result back as root.

Interview Checkpoints

L1: How do you save and exit vim, and exit without saving?

Say first: press Esc, then :wq to save and quit, or :q! to quit and discard changes.

Proof: :x also saves and quits, writing only if the file changed.

Follow-up: What does E37: No write since last change mean?

L2: Replace every occurrence of a hostname in a file using vim.

Say first: substitute across the whole file from Command-line mode.

Proof: :%s/old.example.com/new.example.com/g

Follow-up: How do you confirm each replacement? (Add the c flag.)

L2: Make crontab -e open vim instead of nano.

Say first: set VISUAL or EDITOR, or change the system default.

Proof: export VISUAL=vim in ~/.bashrc, or sudo update-alternatives --config editor on Ubuntu.

Follow-up: Which variable wins when both are set?

L2: Jump to line 120 of a config file that an error message mentions.

Say first: open it at that line.

Proof: vim +120 /etc/nginx/nginx.conf, or :120 inside vim.

Follow-up: How do you show line numbers permanently? (set number in ~/.vimrc.)

L3: A user allowed to edit one file through sudo gained a root shell.

Say first: the rule allowed sudo vim <file>, and vim can run shell commands.

Proof: sudo -l shows (root) /usr/bin/vim /etc/app.conf; inside vim, :!sh runs as root.

Follow-up: How should the rule be written? (sudoedit /etc/app.conf.)

L3: YAML pasted into vim fails to parse even though it looked correct.

Say first: check indentation changes made by auto-indent, and tabs.

Proof: :set list shows ^I tabs and shifted indentation; :set paste before pasting stops auto-indent.

Follow-up: Which tool validates the file before applying it? (yamllint, kubectl apply --dry-run=client.)

Captured on Rocky Linux 10.2 and Ubuntu 24.04.4 LTS (iximiuz Labs microVMs, kernel 6.1.167), 2026-09.