In httpd error_log, it got
icmp open socket: Permission denied
It is because the seLinux blocking the httpd for security reason.
Two solutions:
1. Disable seLinux (high risk)
2. Build a custom policy to unblock partial permission for httpd
To build custom policy, use audit2allow command (may require install)
Ref.: http://wiki.centos.org/HowTos/SELinux
1. install audit2allow module
yum install policycoreutils-python
2. generate preview policy
grep httpd /var/log/audit/audit.log | audit2allow -m httpdcommandlocal > ~/httpdcommandlocal.te
cat ~/httpdcommandlocal.te
3. generate real policy
grep httpd /var/log/audit/audit.log | audit2allow -M httpdcommandlocal
4. apply real policy
semodule -i httpdcommandlocal.pp