Introduction to Linux Services and Daemons

In Linux, a Service is a program that runs in the background and provides important functions like web server, database, or networking.
A Daemon is also a background process, usually started at boot time, which keeps running without direct user control.

Difference Between Service and Daemon

• Service: A program managed by the system (like Apache, MySQL).
• Daemon: A background process that waits to perform tasks (like sshd, crond).
• In simple terms: Daemon = background process, Service = managed daemon.

Managing Services with systemctl

Most modern Linux systems use systemctl to manage services.

systemctl status sshd        # Check status of service
systemctl start sshd         # Start service
systemctl stop sshd          # Stop service
systemctl restart sshd       # Restart service
systemctl enable sshd        # Enable service at boot
systemctl disable sshd       # Disable service at boot

Checking All Services

systemctl list-units --type=service

Old Method Using service Command

In older Linux versions, services were managed using the service command.

service sshd status
service sshd start
service sshd stop

Important Daemons in Linux

• sshd: Secure Shell Daemon (remote login)
• crond: Scheduler Daemon (runs tasks automatically)
• httpd/nginx: Web server Daemons
• mysqld: Database Daemon

Check if a Daemon is Running

ps aux | grep sshd

Summary

Services and Daemons are the backbone of Linux. As an Administrator, you will often start, stop, enable, and check services.
Remember: systemctl is the modern command, while service is older.