Linux Server Security
SSH Key Hardening
SSH is the front door of every Linux server and the most brute-forced service on the internet. Key-only authentication, disabled root login, fail2ban jails, and non-standard ports together eliminate nearly all automated SSH intrusions while keeping legitimate admin access fast.
Key points
- Switch all accounts to ed25519 or RSA-4096 key authentication; disable password auth entirely.
- Set PermitRootLogin to prohibit-password or no, and administer via sudo users.
- Move SSH to a non-standard high port to shed 99% of automated scans.
- Jail sshd with fail2ban: 3-5 failures trigger escalating bans.
- Restrict SSH with AllowUsers/AllowGroups plus firewall source allowlists where possible.
- Enforce idle timeouts (ClientAliveInterval) and disable unused forwarding.
- Audit authorized_keys quarterly and remove keys of departed staff immediately.
- Consider port-knocking or VPN-only SSH for high-value servers.
Field note
The lesson that sticks is usually your own lockout: keep one active session open while you switch to key-only auth, and log in fresh from a second terminal before closing anything.
Frequently asked questions
Will I get locked out switching to key-only SSH?
Not if staged correctly: add keys, verify key login works, then disable passwords, always keeping one active session open during the change.
Is changing the SSH port security through obscurity?
Partially, but it removes nearly all bot noise, which makes real attack attempts visible in logs instead of buried.
Should root login ever be allowed?
Only via console/KVM in emergencies. Day-to-day root over SSH is unnecessary risk.
What about two-factor for SSH?
TOTP on top of keys is excellent for jump hosts and backup servers; we deploy it where the workflow allows.
How Kinetikatech helps with linux server security
You shouldn't have to become an expert in linux server security: Hardening, monitoring, and defending CloudLinux, Rocky Linux, and cPanel servers against malware, brute force, and intrusions, 24/7. That's exactly what Linux Server Security and Server Management is for, setup, hardening, monitoring, and a human on call day and night.