Linux 101 : Discovering the services, the open ports and the running machines on a network

To check the services that are running on our Linux system, we could use the "systemctl" command, it also displays the different statuses of these services:

Below is a short explanation of the options used:

• -t service : to view only the "systemd" units that have the "service" type.
• --state=active : only shows the running services.

We could also check the open "listening" connections using the below command:

We could also use the below command to list all listening "TCP listening " sockets: 

If we want to list only the "listening IPv4 connections" for example, we use the below command:

Mapping the machine:

To check the hosts on the  network "10.1.122.0/24", we could use the below command: 

To do half scans "SYN scan"so we could communicate with the ports of the machine without establishing a full connection, we use the below command:

The "-sS" parameter stands for a "SYN scan".

The different states of the ports in an nmap scan:

• filtered : the port is blocked by a firewall
• open : the port is open and not blocked by a firewall.
• closed : no service is running on that port.

Another useful option is the "-sn", it does not perform any port scans, it only discovers the devices present on the "10.1.122.0/24" network:

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IkbalC

Random thoughts, and observations about our daily lives, to make us reflect about life in general.