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Firewall, can be enabled via [http://www.netfilter.org/projects/iptables/| iptables] the guides [http://www.tecmint.com/basic-guide-on-iptables-linux-firewall-tips-commands/| here] and [http://www.cyberciti.biz/faq/category/iptables/| here] describe iptables configuration.
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Check To protect the server it is important to audit the open ports on the machine. To check listening portsyou can run netstat -tulpn
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[http://selinuxproject.org/page/Main_Page| Security Enhanced Linux(SELinux)] is a kernel level security control mechanism, which enforces a set of rules and procedures for the system. SELinux provides fine grained control for access rights and permissions. To check if it is enabled run sestatus To enable run setenforce enforcing To adjust the SELinux config is available at /etc/selinux/config
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[http://www.fail2ban.org/wiki/index.php/Main_Page| Fail2ban] is an excellent tool that can be used both to combat simple DDoS attacks but also to detect and block brute force login attempts.
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