Linux Terminal & Sysadmin Master Cheat Sheet: 100+ Essential Commands

ls -lah

Lists all hidden files, owners, permissions, and file sizes in KB/MB/GB.

find / -type f -size +100M -exec ls -lh {} \; 2>/dev/null

Locates large files consuming disk space across the entire filesystem.

grep -rnwi "/var/log" -e "error"

Searches case-insensitively for the word "error" in all files under /var/log.

# Compress directory:
tar -czvf backup.tar.gz /path/to/folder

# Extract archive:
tar -xzvf backup.tar.gz -C /target/dir

Creates and unpacks compressed gzip tarballs.

rsync -avzP --delete /source/dir/ user@remote:/target/dir/

Copies files with archive preservation, compression, progress bar, and delta sync.

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub

Enforces correct strict permissions required by OpenSSH.

# Directories to 755:
find /var/www/html -type d -exec chmod 755 {} \;

# Files to 644:
find /var/www/html -type f -exec chmod 644 {} \;

Applies correct standards recursively without breaking subfolder traversal.

chown -R www-data:www-data /var/www/html

Assigns ownership to the web server user.

systemctl status nginx
systemctl restart nginx
systemctl enable --now nginx
systemctl reload nginx

Checks status, restarts, enables on boot, and reloads configs without downtime.

journalctl -u nginx -f --since "30 min ago"

Live tailing of systemd logs for a specific service.

# Find PID by port:
lsof -i :8080

# Kill process gracefully:
kill -15 <PID>

# Force kill:
kill -9 <PID>

Locates the process occupying a specific port and terminates it.

df -hT --exclude-type=tmpfs --exclude-type=squashfs

Displays disk usage per mounted partition with filesystem types.

du -sh * | sort -h

Calculates directory sizes and sorts them in ascending human order.

free -m -h

Displays total, used, free, shared, buffer/cache, and available RAM.

ss -tulpn

Shows TCP and UDP listening ports with associated process names and PIDs.

curl -Iv https://example.com --compressed

Fetches TLS handshake info and HTTP headers without downloading the full body.

ip -c addr show

Displays colorized interface names and IPv4/IPv6 addresses.