Identity and Access Management (IAM): Core Principles for Linux and Cloud Security

Identity and Access Management (IAM) is at the centre of every security framework I have worked with.

Whether on Linux systems or in cloud platforms, controlling who can do what is fundamental. In my experience, organisations often underestimate IAM. They focus on firewalls or malware protection, while leaving access control inconsistent or poorly documented. In this article I set out the principles of IAM and how to apply them across Linux and cloud environments.

1. Why IAM Matters

Principle of least privilege: Users and services should only have the access they need.
Accountability: Every action must be tied to an individual or service identity.
Resilience: Good IAM design prevents a single account compromise from leading to a full breach.
Compliance: Frameworks such as ISO27001, NIST, and GDPR place IAM at the centre of their controls.

I have seen IAM controls make the difference between a contained incident and a full compromise.

2. Identities in Linux

On Linux, IAM starts with user and group management.

Users: Each human administrator should have a personal account. Shared root accounts break accountability.
Groups: Group membership simplifies privilege delegation. For example, adding admins to wheel or sudo rather than writing direct rules.
Service accounts: Non-human accounts used by applications. These should be tightly scoped, non-interactive, and documented.

I often find service accounts created ad hoc all over the place with excessive privileges and no expiry date. This is a risk that can be avoided with better IAM discipline.

3. SSH Key Management

For Linux servers, SSH key management is part of IAM.

Enforce key-based login and disable passwords.
Store keys securely, protected with passphrases.
Rotate keys regularly and remove old ones from authorized_keys.
Maintain an inventory of which keys belong to which users.

Amazingly you can even come across keys that belong to staff who left years ago! That should never happen.

4. sudo and Privilege Delegation

As covered in detail in the sudo article, proper sudo configuration is central to Linux IAM.

Avoid giving blanket ALL privileges.
Delegate only what is required.
Ensure all sudo usage is logged and centralised.

This ensures accountability and reduces the risk of privilege misuse.

5. PAM for Authentication Policy

PAM provides the enforcement point for Linux IAM. With it you can:

Enforce password complexity.
Limit failed login attempts.
Add multi-factor authentication.
Restrict login times.

IAM without enforcement is only theory. Using PAM properly ensures the rules are actually applied.

6. Centralised Authentication

For larger environments, I recommend centralising identities. Common approaches include:

LDAP or Active Directory integration via SSSD.
Kerberos for ticket-based authentication.

This provides consistency and allows quick revocation of access when staff leave. It also simplifies audit reporting.

7. Cloud IAM

In cloud platforms, IAM extends beyond Linux to the control plane itself. I spend significant time helping clients with AWS IAM.

Users and groups: Should be minimised. Use roles instead.
Roles and policies: Attach roles to services and instances, not to long-lived keys.
Policies: Avoid *:* permissions. Write specific actions and resources.
MFA: Mandatory for console access.
Key rotation: Enforce regular rotation of API keys.

You sometimes even see AWS accounts where developers have full administrator rights. Needless to say, this is a serious misconfiguration!

8. Separation of Duties

IAM is not only about technology but also about process.

Administrators should not have blanket access to production and development simultaneously.
Developers should not hold production IAM rights.
Security reviews should be performed by separate personnel.

Clear boundaries reduce insider risk and improve compliance standing.

9. Logging and Monitoring

IAM must be monitored to be effective.

On Linux, forward logs from sudo, auth.log, and PAM to a central SIEM.
In AWS, enable CloudTrail and GuardDuty to monitor IAM actions.
Alerts should be configured for:
- New IAM users created.
- Policy changes.
- Multiple failed login attempts.

IAM logs can be useful for tracking down compromised accounts.

10. IAM Lifecycle

Remember always that IAM is not static. Accounts and permissions change constantly. So a solid lifecycle-oriented approach is required:

Provisioning: Accounts created with the minimum necessary privileges.
Review: Regularly audit accounts, keys, and roles. Remove unused identities.
De-provisioning: Accounts and keys revoked immediately when staff leave.

The weakest point is often de-provisioning. Accounts often remain active long after they should have been removed.

Conclusion

Identity and Access Management underpins security in both Linux and cloud environments. It covers user accounts, SSH keys, sudo, PAM, and cloud IAM roles. Done properly, it enforces least privilege, enables accountability, and supports compliance.

IAM is not exciting technology, but it is essential. Weak IAM controls lead directly to breaches. Strong IAM design, by contrast, prevents small mistakes from turning into major incidents.

Security gaps in Linux and cloud systems risk downtime, data compromise, lost business — and compliance failures.

With 20+ years’ experience and active UK Security Check (SC) clearance, I harden Linux and cloud platforms for government, corporate, and academic sectors — ensuring secure, compliant, and resilient infrastructure.

Contact for Contract Assignments