Linux 111: Troubleshooting and Debugging Techniques

Welcome back! Even the most reliable Linux systems can run into issues — a service that won’t start, slow performance, or strange network behavior. This article introduces essential troubleshooting and debugging techniques to help you identify and resolve problems efficiently.

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Start with the Basics

Begin by checking overall system health. These simple commands can give you a quick overview:

• uptime — See how long the system has been running and load averages
• df -h — Check available disk space
• free -h — View memory usage
• top or htop — Monitor running processes

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Check System Logs

Logs are crucial for understanding what’s going wrong. Key tools and files include:

• journalctl — View system logs (Systemd-based systems)
• dmesg — Check kernel messages, useful for hardware issues
• /var/log/ — Traditional log files like syslog, auth.log, and messages

sudo journalctl -xe
tail -f /var/log/syslog

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Diagnosing Services

If a service isn’t running properly, these commands can help you troubleshoot:

sudo systemctl status nginx
sudo systemctl restart nginx
sudo systemctl enable nginx

Check related logs for deeper insight.

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Debugging Network Issues

• ping — Test connectivity
• ip a — Display network interfaces and addresses
• ss -tuln — View open and listening ports
• traceroute — Trace route to a host

ping 8.8.8.8
ip a
ss -tuln

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Resource and Process Debugging

Identify resource-intensive processes and manage them effectively:

top
ps aux --sort=-%mem | head
kill -9 <PID>

Use strace to trace system calls of a specific process:

strace -p <PID>

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File Permission Issues

Permissions are a common source of problems. Use these commands to investigate and fix them:

ls -l
chmod +x script.sh
chown user:user file.txt

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Debugging Shell Scripts

Use the -x option to run a script in debug mode:

bash -x myscript.sh

Redirect output and error messages for analysis:

./myscript.sh > output.log 2>&1

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Useful Debugging Tools

• lsof — List open files
• tcpdump — Capture network traffic
• gdb — GNU Debugger (for C/C++ programs)
• perf — Performance analysis tools

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Common Issues and Quick Fixes

• System won’t boot: Use a live CD, check GRUB and /etc/fstab.
• Package manager locked: Remove lock files in /var/lib/dpkg/lock.
• Permission denied errors: Double-check permissions, SELinux/AppArmor contexts.

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Best Practices

• Document your troubleshooting steps
• Make one change at a time and test
• Keep backups of configuration files before editing

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Wrapping Up

Mastering troubleshooting is about being methodical and using the right tools. Whether you’re debugging a broken script, a failing service, or a slow server, Linux provides powerful commands to guide you.

Next up: Linux 112: Linux Backup Strategies and Disaster Recovery