httpd: Could not reliably determine the server's fully qualified domain name, using localhost.localdomain for ServerName

In one of our Centos server, i can't restart httpd.
Error :
[root@localhost ~]# /etc/init.d/httpd restart
Stopping httpd:                                            [FAILED]
Starting httpd: httpd: Could not reliably determine the server's fully qualified domain name, using localhost.localdomain for ServerName
(98)Address already in use: make_sock: could not bind to address [::]:80
(98)Address already in use: make_sock: could not bind to address 0.0.0.0:80
no listening sockets available, shutting down
Unable to open logs
                                                           [FAILED]

In nmap i can see port 80 is opened by httpd. I tried to kill the process and httpd but it failed

[root@localhost ~]# netstat -ltnp | grep ':80'
tcp        0      0 0.0.0.0:80                  0.0.0.0:*                   LISTEN      1016/nginx

[root@localhost ~]# ps -wlp1016
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
5 S    99  1016     1  0  80   0 -  5497 ep_pol ?        00:00:00 nginx


[root@localhost ~]# fuser -k -n tcp 80
80/tcp:               1016  1017  1018  1019

[root@localhost ~]# netstat -ltnp | grep ':80'

[root@localhost ~]# /etc/init.d/httpd start
Starting httpd: httpd: Could not reliably determine the server's fully qualified domain name, using localhost.localdomain for ServerName
                                                           [  OK  ]
[root@localhost ~]#

Now i can start httpd in that server, later i noticed that in crontab

[root@localhost html]# crontab -l
3,18,33,48 * * * * killall -6 nginx httpd; sleep 1; /usr/local/nginx/sbin/nginx
[root@localhost html]#

I removed that entry and seems fine. Its like an attack from outside.