This cheatsheet is designed for learners of the Linux Masterclass by Happywala Engineer . It provides quick access to essential Linux commands, organized by category, to help you navigate, manage, and master Linux systems effectively.
Shell and Navigation Basics
Description
Commands
Print working directory pwd
List directory (detailed, human-readable) ls -lah
Change directory (go back / home) cd .., cd ~
Show hidden files ls -a
Path of a command which ls
Command help command --help
Manual page man command
Files and Directories
Description
Commands
Create file (empty) touch file.txt
View file (short/long/paged) cat file.txt, less file.txt, head -n 20 file.txt, tail -n 50 file.txt
Create directory (recursive) mkdir -p dir/subdir
Copy (file/dir) cp source.txt dest.txt, cp -r src_dir dest_dir
Move / rename mv old.txt new.txt, mv file.txt dir/
Remove (file/dir) rm file.txt, rm -r dir, rm -rf dir (dangerous)
Find by name (case-insensitive) find . -iname "pattern"
Find recently modified find . -type f -mtime -1
Locate files (indexed) locate filename (update index: sudo updatedb)
Text Processing Essentials
Description
Commands
Search in files (recursive, numbered) grep -Rni "error" /var/log
Filter columns cut -d',' -f2 file.csv
Sort unique with counts sort file.txt | uniq -c | sort -nr
Replace text (in-place backup) sed -i.bak 's/old/new/g' file.txt
Column arithmetic/reporting awk -F, '{sum+=$2} END{print sum}' file.csv
Word/line/byte counts wc -w file.txt, wc -l file.txt
Permissions and Ownership
Description
Commands
Show permissions ls -l
Change mode (rwx) chmod 644 file, chmod 755 script.sh, chmod +x script.sh
Change owner/group sudo chown user:group file
Set default perms via umask (typical) umask 022
Explain numeric perms quickly r=4, w=2, x=1 → 7 = rwx, 6 = rw-, 5 = r-x, 4 = r--
Users and Groups
Description
Commands
Current user / effective identity whoami, id
Add user / set password sudo adduser alice, sudo passwd alice
Add to group sudo usermod -aG docker alice
List users logged in w, who
Switch user / root shell su - alice, sudo -i
Processes and Jobs
Description
Commands
List processes (wide) ps aux
Find process by name pgrep -a nginx
Kill gracefully/force kill PID, kill -9 PID (last resort)
Foreground/background command &, jobs, fg %1, bg %1
Nice/renice priority nice -n 10 command, renice 5 -p PID
System Info and Monitoring
Description
Commands
Live system view top, htop (install)
Memory usage free -h
CPU/load averages uptime
Disk usage (filesystem) df -h
Directory size summary du -sh dir/
OS release/kernel cat /etc/os-release, uname -r
Services status systemctl status nginx
Networking Basics
Description
Commands
IP addresses / links ip addr, ip link
Reachability ping -c 4 8.8.8.8
DNS lookup dig example.com, nslookup example.com
Routes ip route
Open ports / listeners ss -tulpen
HTTP requests curl -I https://example.com, wget URL
SSH / copy over SSH ssh user@host, scp file user@host:/path
Packages and Software
Task
Commands
Debian/Ubuntu update & install sudo apt update && sudo apt upgrade, sudo apt install pkg
RHEL/CentOS/Fedora install sudo dnf install pkg (or yum on older)
Snap install sudo snap install app
View package files dpkg -L pkg, rpm -ql pkg
Archive and Compression
Description
Commands
Create/extract tar tar -cvf archive.tar dir/, tar -xvf archive.tar
Tar with gzip/bzip2/xz tar -czvf archive.tar.gz dir/, tar -cjvf archive.tar.bz2 dir/, tar -cJvf archive.tar.xz dir/
Extract auto (any tar.*) tar -xvf archive.tar.*
Zip/unzip zip -r archive.zip dir/, unzip archive.zip
gzip/gunzip single file gzip file, gunzip file.gz
Disk, Storage, and Filesystems
Description
Commands
Block devices lsblk
Mount / unmount sudo mount /dev/sdb1 /mnt, sudo umount /mnt
Filesystem check sudo fsck /dev/sdb1 (offline)
Swap summary swapon --show
Create image quickly dd if=/dev/zero of=file.img bs=1M count=100 (be careful)
Services, Logs, and Scheduling
Description
Commands
Manage services sudo systemctl enable nginx, sudo systemctl start nginx, sudo systemctl restart nginx
Journal logs journalctl -u nginx --since "1 hour ago" -n 100 -f
Syslog tail tail -f /var/log/syslog (Debian/Ubuntu), tail -f /var/log/messages (RHEL)
Cron edit/list crontab -e, crontab -l
Sample cron (every 5 min) */5 * * * * /path/script.sh >> /var/log/script.log 2>&1
Shell Productivity and Safety
Description
Commands
Command history / rerun history, !123
Prevent disasters (interactive rm) alias rm='rm -i'
Persistent aliases Add to ~/.bashrc, then source ~/.bashrc
Export environment variable export APP_ENV=prod
Paths echo $PATH, export PATH="$PATH:/opt/bin"
Terminal Editors
Editor
Commands / Shortcuts
Nano quick edit nano file.txt (Ctrl+O save, Ctrl+X exit)
Vim vim file.txt (i insert, Esc :wq save & quit, :q! force quit)
Sudo Essentials
Description
Commands
Run as root sudo command
Edit sudoers safely sudo visudo
Allow a user in sudo group (Debian/Ubuntu) sudo usermod -aG sudo alice
Save The Day
Description
Commands
Tail logs with highlight tail -f app.log | grep --line-buffered -E "ERROR|WARN"
Find big files (>100MB) find / -type f -size +100M 2>/dev/null | sort
List top disk hogs du -ah /var | sort -hr | head -n 50
Check who’s using a port sudo lsof -i :8080
Quick Mental Models
Principle
Explanation
Example
Everything is a file Devices, sockets, and processes expose file-like interfaces, making interaction consistent.
/dev/sda (disk), /proc/cpuinfo (process info)
Pipes compose tools Commands can be chained together to build powerful data flows.
cmd1 | cmd2 | cmd3
Small, sharp tools Use focused commands together rather than one giant command.
grep "error" logfile | sort | uniq -c
Tips, Tricks, Roadmaps, Resources, Networking, Motivation, Guidance, and Cool Stuff ♥
