All the ports are open in Linux by default?

Recently I got a question in my mail from Seth - All the ports are open in Linux by default?

Linux is a kernel - no more, no less. A ton of software is needed in addition to the kernel, and you have a lot of options in regards to what software, and what it needs to do. That's why we have hundreds of distributions and even more if you include embedded devices that all are "Linux" but very very different. So when you ask what "Linux" does, it makes NO SENSE what so ever. You have to be specific here otherwise you're not going to get much of an answer - or rather something that is useful to you.

Presuming you're talking about RHEL or at least CentOS here - and that's a very big if - the firewall is enabled by default yes and will block all but port 22 incoming traffic.

Even some ports like 80 willnot be open on RHEL/CentOS after a default install. The only way you can get http and other services to work without opening the ports in the firewall, is by disabling the firewall (or not installing it).

Btw - note that different installation options results in different configurations. Every installation you do, you should NEVER assume a default setup - always explicitly set the features you depend on.