This article includes a collection of commands and best practices that you can use to improve the security of your Linux servers (RHEL/CentOS). If you have more suggestions, please mention them in the comments. Enjoy the read!

• Remove insecure tools (FTP, telnet, rlogin, rsh, etc.) and use only secure alternatives (SCP, SSH, sftp, rsync, etc.)
• Enable firewall/Iptables
• Disable unwanted services and daemons
• Audit installed packages and remove unwanted ones regularly
• Audit listening network ports and block unwanted ones regularly
• Audit user accounts and disable the unwanted ones regularly
• Enable SELinux
• Turn off IPv6
• Make /boot directory a read-only
• Disable ICMP broadcast requests and harden /etc/sysctl.conf
• Strengthen password policy
• Monitor suspicious user activities
• Disable root login and password authentication for SSH
• Disable shutdown/restart on three-finger salute (Ctrl+Alt +Del)
• Remove desktops
• Fix permissions on world-writable files and no-owner files
• Remove unwanted files/scripts/directories regularly and keep the server clean
• Keep servers up to date
• Collect Syslog regularly
• Set up periodic backups and secure offsite mount points for important files/directories
• Configure intrusion prevention tools at the network level
• Perform security audits regularly
• Improve physical security

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