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Emergency help
- Emergency help for Linux and Unix servers: help yourself first
- Linux server hit by ransomware: what to do right now
- High CPU from a cryptominer: find and remove it
- Website hacked or redirecting: clean it up
- Scan a Linux server for malware (and what scanners miss)
- Find backdoors an attacker left behind on your server
- Locked out of SSH: how to get back into your server
- Reset a forgotten root password (GRUB, rescue mode, cloud)
- Passwords or SSH keys leaked: rotate everything, in order
- Stop brute-force attacks on SSH and web logins
- Server under DDoS or a traffic flood: first steps
- Fix broken apt and dpkg after an interrupted update
- Fix broken dnf, yum and rpm after a failed or interrupted update
- Server won't boot after a kernel update: how to recover
- Disk full on a Linux server: free space safely and fast
- Roll back a bad update on Debian, Ubuntu, RHEL or SUSE
- SSL certificate expired or renewal failed: fix it now
- Server IP blacklisted or sending spam: stop it and get delisted
- Website down: fix 502, 503 and 504 errors fast
- Database won't start: MySQL, MariaDB and PostgreSQL recovery
- Domain or DNS hijacked: how to take your domain back
- Backups that survive ransomware: the 3-2-1 rule in practice
- Restore a hacked or broken server from backup
- Recover accidentally deleted files on Linux
- Server slow, high load or out of memory: quick diagnosis
- Found a suspicious process or open port: investigate safely
- Stuck on an end-of-life OS? Emergency measures until you migrate
- Your host or a scanner reported a vulnerability: what to do
- Abuse complaint: your server is attacking others or sending spam
- Phishing page found on your server: remove it and find the cause
- Personal data leaked from your server? First steps and legal duties
- Top 50 server security questions, answered fast
Vulnerabilities
Linux
Unix & BSD
Server software
Patching guides
- Patching guides for Linux and Unix servers
- Emergency patching playbook: the first hours after a critical CVE
- Am I vulnerable? Check installed package versions against an advisory
- After patching: which services to restart and when to reboot
- Kernel live patching: Livepatch, kpatch, SUSE KLP, Ksplice, KernelCare
- Kernel updates: install, reboot safely and roll back
- Automatic security updates on Linux servers
- Is my OS still supported? End-of-life dates for Linux and Unix (2026)
- Patch many servers at once: Ansible and fleet tools
- Updating PHP fast: distro packages, Sury, Remi and Docker
- Updating Node.js safely: distro packages, NodeSource, nvm, containers
- Patching nginx, Apache httpd and OpenSSL
- Patching containers: rebuild images, don't patch in place
- Kubernetes: patching nodes, control plane and add-ons
- Server hardening checklist: reduce what attackers can reach
- SSH hardening without locking yourself out: keys, root, fail2ban
- Firewall basics for servers: nftables, ufw and firewalld
- Signs your Linux server has been hacked (and how to check)
- Hacked server? The first hour of incident response
- Where to get security advisories for your systems
- MikroTik RouterOS: patch fast and schedule automatic updates
- Scanning servers for missing security updates
- Monitor your server: a step-by-step plan for spotting attacks early
- Schedule automatic security updates on Linux, BSD and macOS
- Logging and monitoring basics for Linux servers
- Intrusion detection on Linux: auditd, AIDE, CrowdSec and Wazuh
- File integrity monitoring: know when system files change
- Get alerted on SSH logins, new users and sudo use
- Spot attacks in web server logs and block them
- Watch processes and outbound connections for signs of compromise
- HTTPS and TLS done right on Linux servers
- Email security for servers: SPF, DKIM, DMARC and MTA-STS
- Security and patching glossary: CVE, CVSS, KEV, EPSS and more
- Server security checklist (printable) for Linux and Unix
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