Linux Checklist Before You Start

Initial System Assessment and Prerequisites

Before installing applications or services, the underlying operating system must be assessed for stability, resource allocation, and baseline security posture. Failure to perform these checks often leads to unpredictable runtime failures or exploitable attack surfaces.

System Health and Patch Management

• Kernel Versioning: Verify that the installed kernel version is supported by all required hardware drivers (NICs, storage controllers). Plan for potential kernel upgrades before application deployment.
• Patch Level Audit: Execute a full system update cycle (e.g., apt update && apt upgrade or yum update) to ensure all packages are running the latest stable versions. Never deploy on known vulnerable software stacks.
• Resource Allocation Check: Confirm adequate CPU core allocation, available RAM, and sufficient swap space configured for expected peak load scenarios. Use tools like htop or vmstat in a baseline test environment.

User and Access Management

Principle of Least Privilege (PoLP) must govern all access points.

• Dedicated Service Accounts: Never run services as root. Create unique, non-privileged user accounts for each application or service component (e.g., svc_web, svc_db).
• Sudo Policy Definition: Implement granular sudoers rules instead of granting full root access. Users should only have the minimum permissions necessary to perform their function.
• Key Management: Utilize SSH key pairs for all remote access. Disable password authentication entirely and enforce mandatory key-based authentication (e.g., using ~/.ssh/authorized_keys).

System Hardening and Security Controls

Layered security controls are paramount to maintaining system integrity.

1. Firewall Configuration: Implement a stateful firewall (iptables or firewalld) immediately. Only explicitly allow necessary ports (e.g., 22/TCP for SSH, 80/TCP, 443/TCP). Drop all other incoming traffic by default.
2. Mandatory Access Control (MAC): Enable and configure SELinux or AppArmor. Set the policy to 'enforcing' mode after initial testing. MAC systems prevent unauthorized actions even if a process is compromised.
3. Audit Logging Setup: Configure auditd rules to monitor critical system calls, file access attempts on sensitive directories (e.g., `/etc/passwd`, configuration files), and privilege escalations.
4. Service Minimization: Disable all unnecessary services (e.g., graphical interfaces, unused networking daemons). Use commands like systemctl list-unit-files --state=enabled to audit running services.

Networking Checklist

Operational Validation and Monitoring

A checklist must conclude with rigorous testing to ensure operational readiness.

Logging and Alerting

• Centralized Logging: Configure all applications and system services to send logs to a centralized, tamper-proof log aggregation solution (e.g., ELK stack, Splunk).
• Log Retention Policy: Define and enforce clear retention policies for security and operational logs.
• Alerting Thresholds: Establish alerts for critical events, such as excessive failed logins, high CPU utilization spikes, or unauthorized file modifications detected by auditd.

Performance Testing

Simulate peak load conditions in a staging environment before production deployment.

1. Stress Testing: Use tools like Apache Bench (ab) or JMeter to simulate expected concurrent user traffic against the application endpoints.
2. Memory Leak Detection: Monitor memory usage over extended periods using profiling tools to detect potential leaks that could lead to eventual service degradation.