IT and cloud certifications · 35 cards · sources listed below

Linux Commands Flashcards

This set covers the shell commands you reach for in the first weeks of using Linux, and that entry-level Linux and sysadmin courses test. The commands and options are standard GNU/Linux behavior written from course knowledge; the linked GNU and man7.org pages are the references to confirm any option, and the find -mtime rounding rule was checked there. Commands vary between distributions and shells, so this is a starter set, not a full reference.

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Free Linux Commands flashcards: 35-card starter set

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Navigation and files (10)

pwd

Prints the current working directory.

ls -l vs ls -a vs ls -h

-l gives a long listing (permissions, owner, size, date). -a includes hidden entries that start with a dot. -h with -l shows sizes in human-readable units.

cd with no argument, cd -, and cd ..

cd alone goes to your home directory. cd - returns to the previous directory. cd .. moves up one level.

cp -r source dest

Copies a directory and its contents recursively. Plain cp copies files only.

mv oldname newname

Moves or renames a file or directory. There is no separate rename command for this.

rm file vs rm -r dir vs rm -f

rm removes files. -r removes directories and their contents recursively. -f ignores nonexistent files and does not prompt. There is no trash or undo on the command line.

mkdir -p a/b/c

Creates the directory and any missing parent directories without error if they already exist.

cat vs less

cat prints a file to the terminal in one go. less lets you scroll through it page by page and search with /.

head vs tail, and tail -f

head shows the first lines (10 by default) and tail shows the last lines. tail -f keeps following new lines as they are written, useful for logs.

Absolute vs relative path

An absolute path starts at the root (/etc/hosts). A relative path starts from the current directory (docs/notes.txt).

Permissions and ownership (7)

What do the numbers 4, 2, 1 mean in chmod?

Read = 4, write = 2, execute = 1. Add them per class: 7 = rwx, 6 = rw-, 5 = r-x, 4 = r--.

What does chmod 755 file mean?

Owner rwx (7), group r-x (5), others r-x (5): the owner can read, write and execute; everyone else can read and execute.

What does chmod 644 file mean?

Owner rw- (6), group r-- (4), others r-- (4): the owner can edit it; others can only read it.

Symbolic chmod: u+x, go-w, a=r

u+x adds execute for the owner. go-w removes write from group and others. a=r sets all classes to read-only.

Who are u, g, o and a in chmod?

u = user (owner), g = group, o = others, a = all of them.

chown alice:staff file

Changes the owner of the file to alice and its group to staff. Usually requires root.

Which permission does a directory need so you can enter it?

Execute (x). Read lets you list names, but you need execute to cd into it or access files inside.

Search and text (8)

grep -i, -v, -n

-i ignores case, -v selects lines that do NOT match, -n prefixes line numbers.

grep -r "text" dir

Searches all files under the directory recursively for lines matching the pattern.

grep -c vs grep -l

-c prints a count of matching lines per file. -l prints only the names of files that contain a match.

grep -E vs plain grep

-E uses extended regular expressions (such as | and + without backslashes). Plain grep uses basic regular expressions.

find . -name "*.log" -type f

Searches from the current directory for regular files whose names end in .log. Quote the pattern so the shell does not expand it.

find -mtime +7

Matches files last modified at least 8 days ago: find rounds the age down to whole 24-hour periods, then tests it as greater than 7.

find ... -exec cmd {} \;

Runs cmd once for every match, with {} replaced by the file name. Ending with {} + instead passes many files to one command invocation.

wc -l

Counts lines (without -l it also gives words and bytes).

Processes, disk, archives and remote access (7)

ps aux vs top

ps aux gives a snapshot list of all processes. top shows a live, updating view of CPU and memory use.

kill PID vs kill -9 PID

kill sends SIGTERM, asking the process to exit cleanly. kill -9 sends SIGKILL, which cannot be caught, so the process dies without cleanup.

df -h vs du -sh

df -h shows free and used space per mounted file system. du -sh shows how much space a directory uses in total.

tar -czf backup.tar.gz dir

Creates (c) a gzip-compressed (z) archive file (f) named backup.tar.gz from dir.

tar -xzf backup.tar.gz -C /tmp

Extracts (x) the gzip-compressed archive into /tmp; -C changes directory before extracting. Use -t to list contents first.

ssh user@host

Opens an encrypted remote shell on host as user, using port 22 by default.

sudo command

Runs one command with another user's privileges, by default root, if your account is permitted in sudoers.

Pipes and redirection (3)

What does the pipe | do?

Sends the standard output of the command on the left to the standard input of the command on the right, for example ps aux | grep ssh.

> vs >> vs <

> writes output to a file, replacing it. >> appends to the file. < feeds a file into a command as input.

2>&1

Redirects standard error (file descriptor 2) to the same place as standard output (1).

What this set covers

Topics

Navigation and files, permissions and ownership, searching text and files, processes, disk usage, archives, ssh and sudo, pipes and redirection.

Best used for

Learning which command and option fits a task, and reading shell one-liners.

Not covered

Package managers, systemd, networking tools, shell scripting and distribution-specific details.

Tip

Try each command in a safe practice directory or virtual machine; rm and chmod can be destructive.

How to study this set

Commands stick when your fingers know them, so combine card review with typing the command in a practice shell.

1
Day 1
Learn navigation and file commands. After each card, type the command in a throwaway directory.
2
Days 2-7
Add permissions. Convert numeric modes to rwx out loud (755 = rwxr-xr-x) and then check with ls -l.
3
Week 2
Practice grep, find and pipes by answering real questions about your own files, such as "which logs are over a week old".
4
Final week
Hide the answer and write the command for a described task, then compare. Review only the misses.

Spaced repetition schedules each card to come back just before you would forget it, so reviews get shorter as your recall gets stronger. Cards you miss come back sooner.

Common mistakes to avoid

Running rm -r without checking the path

There is no trash can on the command line. Run ls on the target first, and avoid a stray space before a slash or wildcard.

Confusing numeric chmod digits

Each digit is a sum for one class (owner, group, others). 7 is rwx, not "seven kinds of access".

Forgetting to quote patterns

Unquoted wildcards in find -name or grep may be expanded by the shell before the command sees them.

Mixing > and >>

> overwrites the file. Use >> when you want to append, especially for logs.

Make your own from your notes

A starter set is a head start, not your whole course. Your class notes, slides and textbook are what your teacher actually tests, so turn them into cards too.

Put the task on the front ("show the last 20 lines of a log") and the command on the back.
Add a second card per command that goes the other direction: command on the front, meaning on the back.
Include one example with real flags, not just the command name.
Avoid cards that list all options of a command; split them into single useful options.

Generate cards from a topic or notes Turn a PDF into flashcards

Linux Commands flashcards: questions

Are these commands the same on every Linux distribution?

The core GNU commands here are widely available on Linux. Options and defaults can differ on other systems such as macOS or BusyBox, so check the man page on your machine.

How do I read a command manual?

Run man followed by the command name, for example man tar. Press q to quit and / to search inside the page.

What is the difference between kill and kill -9?

Plain kill sends SIGTERM, which a program can handle and use to clean up. kill -9 sends SIGKILL, which ends the process immediately without cleanup, so try plain kill first.

Why does chmod 777 get criticized?

It gives every user write and execute access, which is rarely needed and can be a security risk. Prefer the narrowest mode that works.

Sources and review

These cards are an independent study aid, not official exam content, and are not affiliated with or endorsed by any exam body or publisher. They were written by hand and checked against the sources below on 2026-10-17. Always confirm details with your course materials and the current official documents.

GNU Coreutils manual: chmod — Reference for chmod numeric and symbolic modes.
GNU Coreutils manual: rm — Reference for rm options (-r, -f).
tar(1) man page — tar option meanings.
grep(1) man page — grep option meanings.
find(1) man page — find tests and -exec behavior.

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