Linux Security Checklist

1. System Updates and Package Management

Update the system regularly:
sudo apt update && sudo apt upgrade (Debian/Ubuntu)

sudo dnf upgrade (Fedora/RHEL)
Enable automatic security updates
Use only official repositories
Regularly audit installed packages and remove unnecessary ones:
dpkg --list (Debian/Ubuntu)

rpm -qa (Fedora/RHEL)

2. User Account Management

Use strong passwords and implement password policies
Disable root login and use sudo for privileged access
Implement password aging:
sudo chage -M 90 -m 7 -W 7 username
Remove or lock unnecessary accounts:
sudo userdel username or sudo passwd -l username
Use PAM (Pluggable Authentication Modules) for advanced authentication options

3. File System Security

Use appropriate file permissions and ownership
Implement disk encryption using LUKS:
cryptsetup luksFormat /dev/sda2
Use a separate partition for /home, /tmp, and /var
Set proper umask values:
echo "umask 027" >> /etc/profile
Implement file integrity checking with AIDE:
sudo apt install aide (Debian/Ubuntu)

sudo dnf install aide (Fedora/RHEL)

4. Network Security

Configure and enable a host-based firewall (iptables, ufw, or firewalld)
Disable unnecessary network services
Use SSH key-based authentication and disable password authentication:
ssh-keygen -t ed25519

ssh-copy-id user@remote-host
Change SSH default port and limit SSH access:
Edit /etc/ssh/sshd_config
Implement fail2ban to protect against brute-force attacks
Use VPN for remote access

5. Access Control and Privilege Management

Implement SELinux or AppArmor for Mandatory Access Control
Use sudo with specific command permissions instead of full root access
Regularly audit sudo logs:
sudo grep sudo /var/log/auth.log
Implement process isolation using cgroups and namespaces
Use PAM to enforce login restrictions and resource limits

6. Logging and Monitoring

Configure and enable system auditing with auditd:
sudo apt install auditd (Debian/Ubuntu)

sudo dnf install audit (Fedora/RHEL)
Set up log rotation to manage log files
Use a centralized logging system (e.g., rsyslog to a remote server)
Implement log analysis tools (e.g., logwatch, fail2ban)
Monitor system performance and resource usage (e.g., with Nagios or Zabbix)

7. Application Security

Keep all installed applications up-to-date
Use application sandboxing techniques (e.g., Firejail)
Implement Web Application Firewalls (WAF) for web servers
Use SELinux or AppArmor profiles for critical applications
Regularly scan for vulnerabilities using tools like OpenVAS or Nessus

8. Backup and Recovery

Implement a regular backup strategy (e.g., using rsync or duplicity)
Store backups offsite or in a separate physical location
Regularly test backup restoration processes
Implement disaster recovery procedures

Important Note:

This checklist provides a general overview of Linux security best practices. Always tailor these recommendations to your specific Linux distribution, environment, and security requirements. Regularly review and update your security measures to stay protected against evolving threats.