In Stop using Telnet to test ports, I explored several alternative commands and scripts to test TCP connectivity. These commands and scripts range from basic tests to more sophisticated checks, but they are limited to the features provided by supporting tools like Netcat.

Most sysadmins know what Telnet is. Before more robust and secure alternatives like Secure Shell (SSH) appeared, Telnet was the most common way to access remote systems. The Telnet protocol is not encrypted, which is why people no longer use it to provide access to a server. Instead, people use it to check whether a service is listening on a given port, like this: telnet $machine $port. For example:

In August 2022, Dan Walsh (one of the authors of this article) moved out of his role as container runtimes architect at Red Hat to architect for the Red Hat Enterprise Linux (RHEL) for Edge team. Specifically, he has moved to the Red Hat In-Vehicle Operating System (RHIVOS) Containers On Wheels (COW) team.

Imagine you are trying to determine why one of your applications is not performing well. The application logs do not show a specific issue and by the time you checked the server, the problem is gone.

Most likely, you would want to record performance for a given period of time to see what metrics deteriorated on the machine. But you don't have a dedicated agent to take care of that.