Linux Services

Linux services, also known as daemons, are background processes that are usually initiated by the system at boot time and run continuously until the system is shut down. Managing these services involves starting, stopping, enabling, and disabling them, as well as configuring them to start automatically at boot time.

Here's an explanation of the commands related to service management in Linux:

1. SSH Service:

• Ssh -tcp based -22: SSH (Secure Shell) typically runs on TCP port 22. This is the default port used by SSH daemons to listen for incoming connections.

• Service ssh start: This command starts the SSH service on the system.

• Netstat -antp | grep sshd: The netstat command is used to display network connections. Here, it's combined with grep to filter out and display only the SSH connections (sshd refers to the SSH daemon).

• Service ssh stop: This command stops the SSH service.

2. HTTP Server:

• HTTP server - hosting site- tcp -80: Web servers usually listen on TCP port 80 for incoming HTTP connections. This is the default port for web traffic.

• Server apache2 start: This command starts the Apache web server, which is one of the most popular HTTP servers.

• Look into /var/www/: This directory is the default root directory for websites hosted on a Linux web server. It typically contains the HTML and PHP files that make up the website.

3. Service Management in /etc/init.d:

• /etc/init.d/start: This directory contains scripts that can start services on the system. However, the command is incorrect; it usually should be followed by the name of the service you wish to start.

• /etc/init.d/stop: Similar to the start scripts, but this directory does not exist by default. You stop a service by invoking its script with the stop argument, like /etc/init.d/apache2 stop.

4. Service Persistence:

• Update-rc.d ssh enable: This command is used to enable the SSH service to start automatically at boot time.

• Update-rc.d apache2 enable: Similarly, this command enables the Apache web server to start at boot time.

5. Managing Services with rcconf and sysv-rc-conf:

• Rcconf and sysv-rc-conf are TUI (Text User Interface) tools that provide an interface for managing runlevels and services. They provide a more user-friendly way to enable or disable services.

Examples:

Starting SSH service:

sudo service ssh start

Enabling Apache2 service to start on boot:

sudo update-rc.d apache2 enable

Checking the status of the SSH daemon:

sudo netstat -antp | grep sshd

Stopping the SSH service:

sudo service ssh stop

Enabling SSH service using sysv-rc-conf:

sudo sysv-rc-conf

Then you would use the arrow keys to navigate to the ssh service and enable it for the desired runlevels, typically runlevels 2 through 5 for multi-user mode with networking.

Please note that service, update-rc.d, and /etc/init.d/ scripts are part of older init systems like SysVinit. Many modern Linux distributions use systemd as their init system, which replaces these commands with systemctl. For example, to start SSH with systemd, you would use:

sudo systemctl start ssh