devops-notes/07_Linux_Logs_Disk_Management.md

Linux – Logs & Disk Management (Day 7)

Why Logs Are Important in DevOps?

Logs tell you:

• what happened
• when it happened
• why something failed

In production, logs are the FIRST place to check.

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Log Directory

Most Linux logs are stored here:

/var/log

List log files:

ls /var/log

Common logs:

• syslog
• auth.log
• kern.log
• boot.log

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View Log Files

cat (small files)

cat /var/log/syslog

less (recommended)

less /var/log/syslog

Navigation:

• Up / Down arrows
• q → quit

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Live Log Monitoring

tail -f /var/log/syslog

Very useful when debugging live issues.

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Search Inside Logs

grep error /var/log/syslog

Case-insensitive:

grep -i error /var/log/syslog

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Disk Space Management

Check Disk Usage

df -h

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Check Folder Size

du -sh /var/log

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Find Large Files

du -ah / | sort -rh | head -10

⚠️ Use carefully (may need sudo)

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Clear Log Files (Safe Method)

sudo truncate -s 0 /var/log/syslog

❌ Do NOT delete system log files blindly.

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Real DevOps Scenario

Problem: Server disk full

Steps:

1. Check disk usage
2. Identify large directories
3. Clear old logs safely

Commands:

df -h
du -sh
tail -f

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Common Mistakes

• Deleting log files directly
• Ignoring disk alerts
• Not monitoring log growth

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DevOps Rule

✅ Monitor logs regularly
❌ Ignore disk usage

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Summary

Today I learned Linux log monitoring and disk management. These skills are critical for production troubleshooting.