Apache is a freely available Web server that is distributed under an “open source” license. Version 2.0 runs on most UNIX-based operating systems (such as Linux, Solaris, Digital UNIX, and AIX), on other UNIX/POSIX-derived systems
You can easily determine which version of Apache your server is running from the command line with:
Running that command will give you output that will look like this:
[root@host]# httpd -v Server version: Apache/2.4.16 (Unix) Server built: Dec 23 2015 11:28:39 Cpanel::Easy::Apache v3.32.6 rev9999
In this case, Server version shows that the server is running Apache 2.4.16.