Disabling Unneeded Services and Configuring Secure Boot

Minimizing the attack surface is a foundational principle of securing Linux systems. One key method to achieve this is by disabling unneeded services, which reduces potential entry points for attackers and optimizes system resources. Alongside, configuring Secure Boot ensures that the system boots only trusted, signed software, protecting against firmware and boot-level attacks. 

Disabling Unneeded Services

Services running in the background consume system resources and may expose vulnerabilities if not properly maintained or required. Unnecessary services increase the system’s attack surface and potential for exploitation.

Assessment and Identification

1. Evaluate the role and requirements of your server or system.

2. Use system tools to list enabled and active services:

For systemd systems: systemctl list-unit-files --type=service --state=enabled

For SysVinit: list services in /etc/init.d/ or /etc/rc.d/

3. Identify services unnecessary for your use case by understanding their functions.

Disabling Services Safely

1. Use systemctl disable <service-name> to prevent a service from starting at boot.

2. Use systemctl stop <service-name> to stop a running service immediately.

3. For SysVinit systems, use service <service-name> stop and update runlevels with chkconfig <service-name> off.

4. Mask critical services if they must not start manually or automatically via systemctl mask <service-name>.

5. Always check for service dependencies before disabling to avoid breaking functionality with:

Verification and Monitoring

Verification and monitoring of services are crucial to ensure system stability and security. After making changes, always verify service status using commands like systemctl status <service-name> and monitor system logs to track overall behavior. Maintaining a documented list of disabled services further supports auditing and allows for easy recovery if needed.

Configuring Secure Boot on Linux

Secure Boot is a security standard developed under the UEFI firmware specification that ensures a system boots only trusted and signed bootloaders, kernels, and early boot software. It mitigates risks from rootkits, bootkits, and unauthorized modification of boot components.

Enabling Secure Boot

1. Enter the system's UEFI/BIOS setup during boot and enable Secure Boot, usually found in the Security or Boot tab.

2. Use "Custom mode" to enroll your own keys or default vendor keys (e.g., Microsoft's keys) to maintain compatibility with signed software.

3. For Linux distributions, enroll Machine Owner Keys (MOK) to allow loading custom-signed kernels or drivers.

Signing Boot Components

1. Sign kernel images, bootloaders (e.g., GRUB), and modules with private keys.

2. Tools like sbctl or sbsign assist in signing EFI binaries and kernel.

3. Configure GRUB or the bootloader to verify these signatures during boot.