Linux common network issues

One of the problems that I run into several times (and keep forgetting and search for it online) is the lack of connectivity on clean installs of CentOS (and Red Hat systems).

Either the box isn't able to reach box (like MySQL) in the same network or simply you can't make any internet requests from that box.

I spend time trying to look for issues in iptables, network connectivity (like switches, routers, cables), proxies, etc., when normally the issue (99% of the times for me) is simply misconfiguration of SELinux module (probably because I use Debian more often...).

If you are like me, check the SELinux configs first before you waste time looking for issues elsewhere:

getsebool -a | grep httpd

If you get the following in the output:

httpd_can_network_connect --> off

The solution is simple:

setsebool -P httpd_can_network_connect on

This will allow HTTPD scripts and modules to connect to the network.

In case that doesn't work for you, edit /etc/selinux/config file and locate the line that says SELINUX=enforcing and change it to SELINUX=disabled. You will need to reboot, but it will solve your problem.

If you are like me, check that before you waste time looking for issues elsewhere (easy to check that, then to spend too much time for other issues).