Here are some common ways to increase the security of a Linux server like Ubuntu Server, Alma Linux, Debian etc.:
- Keep the operating system up to date: Ensure that the operating system and software installed on the server are always updated with the latest patches to address any security vulnerabilities that are discovered.
- Use a firewall: Install a firewall on the Linux server to block unwanted access. Some Linux distributions have built-in firewalls that can be enabled, such as iptables and firewalld.
- Limit SSH access: Make sure that only users with the necessary permissions can connect to the server via the SSH protocol. Limit the number of failed login attempts and use SSH keys for authentication.
- Install security software: Install security software such as antivirus, anti-malware, and IDS (intrusion detection system) on the server to monitor and protect the system from unwanted attacks.
- Encrypt sensitive data: If there is sensitive data stored on the server, be sure to encrypt the data so that it cannot be accessed by unauthorized parties.
- Manage user access permissions: Ensure that only users with the necessary permissions can access the system and files on the server. Manage user access permissions carefully.
- Install SSL/TLS: If your server provides web services, be sure to install SSL/TLS certificates to secure data sent over HTTPS from MITM attacks.
- Back up regularly: Always back up data regularly to protect your data from loss due to attacks, damage, or hardware failure.
In addition, there are several specialized software tools that can be used to improve the security of a Linux server, such as fail2ban to protect the server from repeated login attempts and SELinux (Security-Enhanced Linux) to increase system security by adding stricter security policies.