7 Critical Linux Logs You Should Review After a Security Incident

✍️ Full Blog Content:

Intro:

The first hour after a security incident is crucial. Whether it’s a brute-force attempt, a misconfigured firewall, or worse, your Linux logs hold the story of what really happened.
Here are 7 log files that I immediately review when investigating a suspected breach — on both Ubuntu and Red Hat servers.

1. /var/log/auth.log (Ubuntu) / /var/log/secure (Red Hat)

Tracks:

• SSH logins
• Failed sudo attempts
• Successful escalations

✅ Tip: Look for:

grep "Failed password" /var/log/auth.log
grep "Accepted password" /var/log/auth.log

2. /var/log/syslog (Ubuntu) / /var/log/messages (Red Hat)

General system events.

✅ Check for:

• Service crashes
• Unauthorized daemon restarts
• Kernel warnings

3. /var/log/faillog

Summarizes all failed login attempts per user.