Service Management (systemctl)

Essential commands for managing background services.

# Start, Stop, Restart
systemctl start nginx
systemctl stop nginx
systemctl restart nginx

# Enable on boot
systemctl enable nginx

# View logs (real-time)
journalctl -u nginx -f

Permissions (chmod/chown)

Numeric reference: Read=4, Write=2, Execute=1.

# Common permissions
chmod 755 file.sh   # rwx-rx-rx (Owner full, others read/exec)
chmod 644 file.txt  # rw-r--r-- (Owner read/write, others read)
chmod +x script.sh  # Make executable

# Change owner
chown user:group file.txt

Common Standard Ports

List of well-known ports for TCP/UDP services.

21   : FTP (File Transfer)
22   : SSH (Secure Shell)
25   : SMTP (Email Sending)
53   : DNS (Domain Name System)
80   : HTTP (Web Unsecured)
443  : HTTPS (Web Secured)
3306 : MySQL / MariaDB
5432 : PostgreSQL

Git Cheat Sheet

Standard workflow for version control.

# Initialize & Commit
git init
git add .
git commit -m "Initial commit"

# Branching
git checkout -b feature/new-login
git push -u origin feature/new-login

# Undo last commit (soft)
git reset --soft HEAD~1

HTTP Status Codes

200 OK             : Success
201 Created        : Resource created
301 Moved perm.    : Permanent redirect
400 Bad Request    : Client syntax error
401 Unauthorized   : Authentication required
403 Forbidden      : Server refuses action
404 Not Found      : Resource missing
500 Internal Error : Generic server crash
502 Bad Gateway    : Upstream error