Ok I understand. But what about the problem with starting Ajenti? 

Every time I reboot my server I have to use the commands: 

service ajenti restart

and I have to login into ajenti panel and go to Websites and press Restart Websites otherwise I get the error Bad Gateway

if I execute the command setenforce 0 (disable SELinux) is working. My question is should't SELinux remain enabled?

I have the limit set to 1000000 and still dowes not work. I've checked the log and I still get the error.

1. I have deleted phpMyAdmin for the moment 
2. I have not modified anything but I followed the instructions and rebooted my server and still nothing.

I see some of these errors:
[warn] 1566#0: server name "192.168.2.5/phpMyAdmin" has suspicious symbols in /etc/nginx/conf.d/phpmyadmin.conf:10

And a lot of these:
[alert] 2685#0: setrlimit(RLIMIT_NOFILE, 100000) failed (1: Operation not permitted)

1. Still does not work
2. Yes
3. I just emailed the files in an archive to you. The email has the subject: Ajenti 403 Forbidden - Andrei R.
4. I forgot to mention that I use CentOS 7