How to Start, Stop, and Restart Services in Linux

Managing services in Linux depends on the system’s init system. Most modern distributions use systemd, while older ones might still use SysV init.

---

1. Using systemd (Most Modern Distributions)

Most Linux systems (Ubuntu 16.04+, Debian 8+, CentOS 7+, etc.) use systemd.

Start a Service

sudo systemctl start <service-name>
# Example:
sudo systemctl start nginx

Stop a Service

sudo systemctl stop <service-name>
# Example:
sudo systemctl stop sshd

Restart a Service

sudo systemctl restart <service-name>  # Full restart
sudo systemctl reload <service-name>  # Reload config (if supported)
# Example:
sudo systemctl restart apache2

Reload Configuration (Without Restart)

sudo systemctl reload <service-name>  # Only reload config files
# Example:
sudo systemctl reload nginx

Check Service Status

sudo systemctl status <service-name>
# Example:
sudo systemctl status mysql

Enable/Disable Service at Boot

sudo systemctl enable <service-name>   # Start automatically at boot
sudo systemctl disable <service-name>  # Disable auto-start
# Example:
sudo systemctl enable docker

Restart vs. Reload

• restart: Stops and starts the service (downtime).
• reload: Applies new configuration without stopping the service (no downtime).

---

2. Using Legacy service Command (SysVinit)

Older systems (or compatibility mode) may use service.

Start/Stop/Restart

sudo service <service-name> start
sudo service <service-name> stop
sudo service <service-name> restart
# Example:
sudo service mysql restart

---

3. Using /etc/init.d Scripts (Legacy Systems)

For very old systems or custom scripts:

sudo /etc/init.d/<service-name> start
sudo /etc/init.d/<service-name> stop
# Example:
sudo /etc/init.d/nginx restart

---

Common Services

Replace <service-name> with:

• nginx/apache2 (web servers)
• mysql/postgresql (databases)
• ssh/sshd (SSH server)
• docker (container service)
• ufw (firewall)

---

Key Tips

• List All Services:

  systemctl list-unit-files --type=service

• Check If systemd Is Used:

  ps -p 1 -o comm=  # Returns "systemd" if running

• View Logs:

  journalctl -u <service-name>  # systemd logs

---

Troubleshooting

• Permission Denied: Use sudo.
• Service Not Found: Check the exact service name with systemctl list-unit-files.
• Failed to Start: Check logs with journalctl -u <service-name>.

---

Example Workflow

1. Restart Nginx after config changes:

   sudo systemctl reload nginx  # Or restart if reload isn't supported

2. Disable MySQL auto-start:

   sudo systemctl disable mysql

3. Stop a service temporarily:

   sudo systemctl stop apache2