Linux Core Flashcards

Command to list directory contents

ls

Option to show long listing format with ls

ls -l

Option to list all files including hidden with ls

ls -a

Command to display current working directory

pwd

Command to change directory

cd

Change to parent directory

cd ..

Shortcut to home directory

cd ~

Reuse previous working directory

cd -

Command to create a file

touch

Command to create a directory

mkdir

Option to create parent directories as needed with mkdir

mkdir -p

Command to remove a file

rm

Command to remove directory recursively & force

rm -rf

Command to copy files

cp

Option for recursive copy

cp -r

Command to move/rename a file

mv

Command to display contents of file

cat

Command to concatenate multiple files into one

cat file1 file2 > combined.txt

Command to view file with pagination

less

Quick exit from less

q

Display first 10 lines of a file

head

Display last 10 lines of a file

tail

Follow log file in real time

tail -f

Search for pattern in files

grep "pattern"

Make grep case‑insensitive

grep -i

Count lines matching pattern

grep -c

Show line numbers with grep

grep -n

Search recursively with grep

grep -r "pattern"

Find files by name (current dir)

find . -name "*.txt"

Find and delete empty files

find . -type f -empty -delete

Search command history

Ctrl + r

Repeat last command

!!

Run previous command starting with string

!ls

Get help for a command

man

Quick help output (many commands)

--help

What does 'apropos' do

Search man page names/descriptions

Display path of executable

which

Show command location in PATH list

type -a

Print environment variables

printenv

Set environment variable for current session

export VAR=value

Change file permissions (symbolic)

chmod u+x

Change file permissions (numeric)

chmod 755

Change owner of file

chown

Change owner & group

chown :

Change group ownership

chgrp

Permission bits: read

4

Permission bits: write

2

Permission bits: execute

1

Special permission setuid value

4### (chmod 4755)

Octal 644 corresponds to

rw-r--r--

Symbolic to remove execute for others

chmod o-x

Command to change default perms mask

umask

Default umask for regular users

022

File that stores user accounts

/etc/passwd

File that stores encrypted passwords

/etc/shadow

Command to switch user

su -

Command to run cmd as root

sudo

File that configures sudo privileges

/etc/sudoers

Command to edit sudoers safely

visudo

Command to add user

sudo useradd

Show snapshot of current processes

ps aux

Show tree view of processes

pstree

Interactive process monitor

top

Improved top with colors & sorting

htop

Kill process by PID

kill

Force kill process

kill -9

Find PID by name

pgrep

Run command in background

&

Bring bg job to foreground

fg

List jobs in current shell

jobs

Nice value meaning

CPU scheduling priority

Change priority of running process

renice

Display system uptime and load

uptime

Check disk usage human readable

df -h

Check directory size summary

du -sh

Show memory usage

free -h

Display block device information

lsblk

Display mounted filesystems

mount | column -t

Mount ISO image

sudo mount -o loop cd.iso /mnt

Unmount filesystem

sudo umount /mnt

Show IP addresses (modern)

ip addr

Bring interface up

sudo ip link set eth0 up

Check network connectivity

ping

Traceroute to host

traceroute

DNS lookup command

dig

Simple HTTP request tool

curl

Transfer files over SSH

scp file user@host:/path

Secure shell login

ssh user@host

Package index update (Debian)

sudo apt update

Install package (Debian)

sudo apt install

Remove package (Debian)

sudo apt remove

Upgrade all packages (Debian)

sudo apt upgrade

Package manager for Red Hat

yum or dnf

Show package that owns a file (dpkg)

dpkg -S

List all installed packages (RPM)

rpm -qa

Enable a service with systemd

sudo systemctl enable

Start a service

sudo systemctl start

View service status

systemctl status

View systemd journal logs

journalctl -xe

Reboot the system

sudo reboot