# Linux Server Security: Hardening Your Infrastructure Against Modern Threats
Linux dominates server deployments. Cloud instances, containers, on premises infrastructure. The open source operating system runs the majority of internet facing workloads. This prevalence makes Linux a primary target for attackers.
Default installations trade security for convenience. Getting started is easy. Staying secure requires deliberate hardening. The gap between default and secure represents vulnerability that attackers actively exploit.
## Foundation Security
**Minimal installation** reduces attack surface. Install only packages required for the server's function. Each additional package is potential vulnerability. Web servers do not need development tools. Database servers do not need web servers.
**System updates** close known vulnerabilities. Establish patching cadence appropriate to system criticality. Automated updates for security patches reduce exposure time. Test before applying to production where stability matters.
**User accounts** require careful management. Disable or remove default accounts. Require strong passwords or key based authentication. Implement account lockout policies. Regular review identifies stale accounts requiring removal.
**Privilege management** follows least privilege. Users receive minimum necessary permissions. Sudo configuration grants specific elevated capabilities. Root login is disabled in favour of privilege escalation.
## Network Hardening
**Firewall configuration** controls traffic flow. Default deny policies block all except explicitly permitted. Filter both ingress and egress traffic. Document rules and review regularly.
**Service exposure** should be minimal. Bind services to specific interfaces when possible. Internal services do not need internet exposure. Use SSH tunnels or VPNs for administrative access.
**SSH hardening** protects the primary access vector. Disable password authentication. Use key based access only. Consider non standard ports if appropriate. Limit users who can connect. Implement fail2ban to block brute force attempts.
**Network segmentation** contains breaches. Separate application tiers into network zones. Filter traffic between zones. Compromise of one system does not grant access to all.
## Access Controls
**SELinux or AppArmor** provide mandatory access control. Traditional Unix permissions are discretionary. Root can bypass them. Mandatory access control applies even to root processes. Compromised applications cannot exceed their defined policy.
**File system permissions** deserve systematic review. Identify and remediate world writable files and directories. Audit setuid and setgid binaries. Ensure proper ownership throughout.
**Capabilities** replace blanket root privilege. Rather than running as root, grant specific capabilities. A web server needs to bind port 80, not full root access. Reduced privilege limits breach impact.
## Monitoring and Detection
**Audit logging** captures security relevant events. Configure auditd to log authentication, privilege escalation, file access, and network connections. These logs enable detection and forensics.
**Integrity monitoring** detects unauthorised changes. Tools like AIDE baseline file systems and alert on modifications. Attackers frequently modify binaries to maintain persistence. Detection enables response.
**Centralised logging** preserves evidence. Attackers modify local logs to cover tracks. Remote logging defeats this technique. Ensure logs ship in real time.
**Intrusion detection** identifies active threats. Network based detection monitors traffic patterns. Host based detection watches system behaviour. Correlation across sources improves detection accuracy.
If your organisation needs help securing Linux infrastructure or implementing defence in depth, contact us through our contact page. We provide practical security improvements that protect production systems.