Harden a Linux server by reducing what is installed and exposed, keeping its supported software patched, limiting who can do what, protecting remote administration, and making security activity visible in logs. No single setting makes a server secure. Use the 40 checks below as prompts to build a baseline that fits your distribution, release, workload, and compliance needs—not as a universal set of commands.
Before changing a production host, identify its role and current exposure, confirm you have a recovery path, and test changes that could interrupt access or services. Commands and control names differ among distributions and releases. Where this checklist names Ubuntu tools, treat them as Ubuntu-specific examples and check the documentation for the release you actually run.
Inventory the server and choose a baseline
Start by establishing what the machine is supposed to do and what it currently exposes. Ubuntu Security Guide can audit systems and apply or customize CIS Benchmark and DISA-STIG profiles. CIS describes its benchmarks as consensus-developed secure-configuration guidance; a benchmark result is not a guarantee that a host is secure.
1. Record the distribution and release
Document the Linux distribution, release, and support status. Security procedures and package commands vary, and a release may no longer receive the updates you expect.
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2. Write down the server’s role
Describe the workloads the host must run, who administers it, and which systems it must communicate with. This gives you a basis for deciding whether a package, account, port, or service is necessary.
3. Inventory listening ports
Identify the ports accepting connections and the processes behind them. Compare the results with the intended network flows; investigate unexpected listeners before changing firewall rules.
4. Inventory installed packages
Record installed software and identify packages that are not needed for the server’s role. A smaller software footprint generally means fewer components to maintain and assess.
5. Select a release-matched security profile
If you use CIS Benchmark or DISA-STIG guidance, choose a profile that matches the system and your requirements. Ubuntu Security Guide supports auditing and applying CIS Benchmark and DISA-STIG profiles; CIS lists benchmark material for multiple Ubuntu releases.
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Run an assessment before applying a profile or changing a group of settings. Review each finding in context so you understand whether it applies and what could break if you remediate it.
7. Tailor controls to the workload
Do not disable a service or impose a setting solely to maximize a checklist score. Decide whether each control fits the host’s role, exposure, authentication stack, and compliance obligations.
8. Test changes before production
Apply consequential changes in a test environment or during a controlled maintenance window. Keep a rollback or console-recovery route available, especially when changing remote access, firewall rules, or authentication.
Keep software supported and updated
Ubuntu recommends regular updates to address known vulnerabilities and documents unattended-upgrades for automated security updates and bug fixes. Update automation is useful only if someone monitors its outcome and handles any required restart under the operator’s maintenance policy. Other distributions have their own package and update tools.
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9. Install security updates regularly
Use the package-management process for your distribution to apply supported security updates. On Ubuntu, the documented example is apt update && apt upgrade; do not assume that command is appropriate for every Linux distribution.
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10. Automate updates when operations allow
Consider unattended security updates where they fit your uptime, testing, and change-control requirements. On Ubuntu, unattended-upgrades is the documented mechanism; verify its configuration and scope for your release rather than assuming every update is installed automatically.
11. Monitor update results
Check whether updates completed, failed, or require attention. Automation without a way to detect failures can leave the host believing it is maintained when it is not.
12. Plan for restarts
Decide how your environment identifies updates that need a reboot or service restart, and schedule that work according to your maintenance policy. Do not treat an installed update as proof that a running service is already using it.
13. Remove unused packages
Uninstall software the server no longer needs, after checking dependencies and operational ownership. Avoid removing components just because their purpose is not immediately obvious.
14. Minimize installed services
Review enabled services and keep only those required for the workload. Disable an unnecessary service using the distribution’s supported service-management procedure, then verify that dependent applications still work.
15. Use supported package sources
Prefer repositories and packages maintained for your distribution and release. Know which third-party sources are configured and who is responsible for their updates.
16. Track the release support lifecycle
Check the support terms and dates for the specific release, including any applicable subscription or extended-support arrangements. Do not infer the support window from the distribution name alone.
Control identities and administrative privilege
Use individual accounts and least privilege so administrative actions can be attributed and users have only the access their work requires. Ubuntu and CISA both recommend least privilege. Authentication choices should match the systems and services that actually support them.
17. Give administrators named accounts
Use individually assigned accounts for routine administration rather than shared administrator identities. Individual accounts make access easier to review and actions easier to attribute.
18. Avoid routine root login
Do not use the root account for ordinary interactive work. Restrict direct root access in a way compatible with your recovery procedures and the distribution’s guidance.
19. Elevate privileges for administrative tasks
Use the distribution’s supported privilege-elevation mechanism when elevated access is needed, rather than conducting all work in a root session. On systems configured for it, that commonly means sudo; verify local policy and access before relying on it.
20. Grant only required permissions
Review file, directory, and command permissions against the job each account or service performs. Avoid broad access grants that make routine compromise more consequential.
21. Remove stale accounts
Disable or remove accounts that no longer have a legitimate owner or purpose, following retention and recovery requirements. Check whether services or scheduled tasks depend on an account before deleting it.
22. Review group membership
Inspect privileged and service-related groups for members who no longer need access. Treat group membership as an access grant, not as a harmless administrative detail.
23. Require strong authentication
Choose authentication methods appropriate to the access path and enforce the strongest options supported by the system. Protect credentials against reuse and unauthorized disclosure.
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For company-system access, CISA recommends phishing-resistant multifactor authentication and gives hardware-based PKI and FIDO as examples. A FIDO security key is an option only when the identity and authentication flow in use supports it; it is not a universal Linux-server requirement.
Limit network exposure and unnecessary services
Permit only traffic the workload needs, restrict management paths, and reassess exposure after deployment. Ubuntu identifies UFW as its firewall tool, while CISA recommends disabling unnecessary services and using network segmentation. Firewall syntax and service controls vary by distribution and environment.
25. Enable a suitable host firewall
Use a firewall supported by your distribution and operational tooling. Ubuntu documents UFW as an option; select and configure the appropriate tool for the host rather than copying a command intended for another system.
26. Allow only required inbound ports
Build inbound rules from the server’s documented services and intended clients. Avoid broad allow rules where narrower source or destination restrictions are practical.
27. Restrict management access to trusted paths
Limit administrative access to the network paths and source systems that need it, using controls supported by your architecture. Do not expose a management service publicly by default.
28. Disable unused network services
Turn off services that are not required for the host’s role, after checking dependencies. Recheck listening ports after the change to confirm the intended exposure.
29. Avoid obsolete or plaintext protocols
Prefer currently supported, protected protocols for administration and data transfer. Remove legacy protocols when they are not required; where compatibility prevents removal, account for the residual risk in the network design.
30. Segment server networks where appropriate
Place servers in network segments that reflect their role and limit unnecessary communication between systems. CISA recommends network segmentation; the right boundaries depend on the workload and architecture.
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31. Recheck exposed ports after deployment
Repeat the listening-port and firewall review after installing or changing applications. A deployment can introduce a listener or rule that was absent from the initial baseline.
32. Document intended network flows
Record which systems should connect to the server, on which services, and for what purpose. Use that record to review firewall changes and investigate unexpected connections.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Log activity and reassess the baseline
CIS Control 6 lists audit logging, central log management, and regular review among its safeguards. Logging is useful only when records are available, protected, and examined in a way that suits the environment; choose retention and alerting practices based on operational and legal requirements.
33. Activate security audit logging
Enable the audit and security logs appropriate to the distribution and services. Confirm that the events important to your incident response and operational needs are being recorded.
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34. Protect log access and integrity
Restrict who can read, change, or delete logs, and protect records against accidental loss or unauthorized alteration. Ensure log-management permissions do not simply mirror broad administrator access.
35. Centralize logs where practical
Forward relevant logs to a central service when your infrastructure supports it. Central storage can preserve records outside the host and make review across systems more practical.
36. Provide adequate log storage
Set storage and retention appropriate to the volume of events and your response or compliance needs. Monitor capacity so logging does not silently stop or consume space needed by the workload.
37. Review logs regularly
Assign responsibility for examining security-relevant records and following up on suspicious or unexplained events. Set a review cadence that reflects the server’s exposure and operational context.
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Configure alerts for events that warrant investigation, and route them to someone able to respond. Tune them to reduce noise while preserving visibility into activity that matters.
39. Rerun baseline audits after changes
Reassess the host after substantial configuration or software changes. Compare new findings with the intended baseline and investigate unexpected drift.
40. Revisit the baseline when the host changes
Review the baseline when the server’s software, network exposure, authentication path, compliance target, or role changes. A configuration that suited its earlier purpose may no longer be appropriate.
Choose and apply a hardening baseline responsibly
When choosing between a tailored configuration and a formal profile, compare the system and operational fit rather than treating any one profile as universally correct.
| Decision factor | What to check |
|---|---|
| Distribution and release | Confirm that the guidance and tools support the exact distribution and release in use. Ubuntu Security Guide and CIS benchmark material cover particular Ubuntu releases; check the current version before applying controls. |
| Server role | Match controls to required services, access paths, and workload dependencies. A setting that is suitable for one role may disrupt another. |
| Compliance target | Use the profile required by your organization or jurisdiction, such as an applicable CIS Benchmark or DISA-STIG profile. Determine which controls apply to the actual system. |
| Operational impact and rollback | Assess the risk of service interruption or loss of administrative access, and test how to reverse or recover changes. |
| Automation and audit | Check whether the chosen tooling can audit and apply the profile, how changes are reviewed, and how outcomes or failures are monitored. |
| Authentication compatibility | Verify that required authentication controls work with the server’s identity provider, administrator workflow, and supported services. |
Use current documentation from Ubuntu/Canonical, CIS, CISA, and your distribution for release-specific procedures. The guidance cited here establishes broad control areas, not a universal command set; exact release support, profile versions, and operational requirements can change.
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