8 Log Files Every Linux Admin Should Monitor Daily

Intro:

You can’t protect what you don’t monitor. Linux logs hold the answers to failed logins, strange commands, broken services, and suspicious activity — but only if you know where to look. These 8 log files are the first places I check during audits and daily health checks on both Ubuntu and Red Hat servers.

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

Tracks login attempts, sudo usage, and brute-force attacks.

🔍 Look for:

• Failed password
• Invalid user
• sudo: entries for privilege escalation

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

The system-wide event log.

🧠 Why it matters:
If something weird is happening — kernel panic, service failure, hardware issues — it often shows up here first.

3. /var/log/cron

Shows scheduled jobs run via cron.

🔍 Watch for:

• Unexpected or unknown jobs
• Errors in job output
• Signs of malware persistence using…