18.MariaDB Troubleshooting

Lab Information

There is a critical issue going on with the Nautilus application in Stratos DC. The production support team identified that the application is unable to connect to the database. After digging into the issue, the team found that mariadb service is down on the database server.

Look into the issue and fix the same.

Lab Solutions

🧭 Part 1: Lab Step-by-Step Guidelines

Objective

Fix MariaDB service on DB Server (stdb01) so the application can connect again.

1️⃣ Login to Jump Host

ssh thor@jump_host.stratos.xfusioncorp.com

Password:

mjolnir123

2️⃣ Connect to DB Server

ssh peter@stdb01

Password:

Sp!dy

3️⃣ Switch to Root

sudo -i

4️⃣ Check MariaDB Status

systemctl status mariadb

5️⃣ Check Error Logs (CRITICAL STEP)

journalctl -xeu mariadb.service

🧠 Root Cause Identified

Key lines:

Socket file /var/lib/mysql/mysql.sock exists.
No process is using /var/lib/mysql/mysql.sock

👉 This means:

Stale socket file is blocking MariaDB startup

👉 This tells you the exact root cause.


🔴 Case 1: Remove the stale socket file

rm -f /var/lib/mysql/mysql.sock
rm -f /var/lib/mysql/*.pid

chown -R mysql:mysql /var/run/mariadb
chmod 755 /var/run/mariadb

chown -R mysql:mysql /var/lib/mysql

🔴 Case 2: Start MariaDB again

systemctl start mariadb

🔴 Case 3: Status MariaDB again

systemctl status mariadb

🧠 Part 2: Simple Explanation (Beginner Friendly)

What went wrong

MariaDB needs two things:

Type                        Path
Data files                  /var/lib/mysql
Runtime files (socket/pid)  /var/run/mariadb

Your issue
Data directory      ✔ OK
Runtime directory   ❌ missing

So MariaDB:

tries to create socket → fails → exits

⚡ Golden Troubleshooting Pattern (IMPORTANT)

Whenever a service fails:

Step 1

systemctl status SERVICE

Step 2

journalctl -xeu SERVICE

Step 3

Identify pattern:

Error                       Fix
socket exists               remove .sock
permission denied           chown
cannot create pid/socket    fix /var/run


✅ Final Result

Component   Status
MariaDB     running
Socket  r   ecreated
App connected

🎯 Key Takeaway
Service failure ≠ always config issue
Often it's filesystem (permissions, directories, sockets)
---
##### **Resources & Next Steps**
##### 📦 Full Code Repository: [KodeKloud Learning Labs](https://github.com/thukhakyawe/100-Days-Of-DevOps-KodeKloud-Challenges-Solutions)
##### 📖 More Deep Dives: [Whispering Cloud Insights](https://thukhakyawe.hashnode.dev/) - Read other technical articles
##### 💬 Join Discussion: [DEV Community](https://dev.to/thukhakyawe_cloud) - Share your thoughts and questions
##### 💼 Let's Connect: [LinkedIn](https://www.linkedin.com/in/thukhakyawe/) - I'd love to connect with you
---
##### **Credits**
##### • All labs are from: [KodeKloud](https://kodekloud.com/)
##### • I sincerely appreciate your provision of these valuable resources.
---