A Technical I.T./DevOps Blog
Problem scenario
You want to monitor network traffic on an EC-2 server’s NICs. You are not sure what to look for or what a baseline should look like. What do you do?
Solution
1. Install dstat. With a CentOS/RHEL/Fedora server, run this: sudo yum -y install dstat
2. Run this command: dstat -nt
3. With no network activity beyond the PuTTy session to the EC-2 server,
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Continue reading “How Do You Interpret the dstat Utility’s Results on a Linux Server in AWS?”
Problem scenario
You have some Pods in Kubernetes that you want deleted. What should you do?
Solution
1. Find the names. You can run this to find out: kubectl get pods
2. Run this command, but replace “foobar” with the name of the pod you want deleted: kubectl delete pods foobar
3. That should be it. Run kubectl get pods to verify deletion was successful.
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Problem scenario
You run kubectl get pods and you find many or all are not ready. What should you do?
Solution
Run this command: kubectl describe pods
The resulting output should help you.
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Continue reading “How Do You Troubleshoot Kubernetes when Pods Are Not Ready?”
Problem scenario
Your Java program returns this message: “java.sql.SQLException: No database selected”
What should you do?
Possible Solution #1
Your SQL statement was appropriate for a database but not for the circumstance of connecting to a SQL instance. Try show databases; instead of the SQL you were running.
Possible Solution #2
Did you connect to the SQL instance you thought you connected to?
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Problem scenario
You use the mailq command. You see several emails have timed out. These emails are essentially in an “outbox” and a future delivery attempt is in the near future. How do you produce a list of the mail queue IDs by themselves?
Solution
If you want a list of the mail queue IDs in the queue, run this:
mailq | awk ‘{print $1}’ | grep -v ‘[[:punct:]]’ | sort | uniq
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Continue reading “How Do You Get a List of Mail Queue IDs and Nothing Else?”
Problem scenario
You have a sed command in a script, but you get an error like one of the following:
sed: -e expression #1, char 1: unknown command: ” sed: -e expression #1, char 1: unknown command:”‘
How do you troubleshoot this?
Solution
You may need to assign variables like this:
var1=” foo””‘”” bar” # Place quotes around any unusual characters (e.g.,
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Problem scenario
You have a MySQL database. Rather than use a SQL front-end application, you want to write a Java program that will run a SQL statement against the database. What should you do?
Solution
1. Install the Java compiler if it is not already installed. If you need assistance, see this posting.
2. Run this command:
curl -Lk https://www.javatpoint.com/src/jdbc/mysql-connector.jar >
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Continue reading “How Do You Run a Java Program to Run SQL Commands Against a MySQL Database?”
Problem scenario
You have configured a Docker container with a web service (e.g., Apache web server or Nginx). You configured the listening, external port to be 80 or a different port number. You find the web server (either Apache or Nginx) is not working from a web browser. How do you find what is wrong?
Solution
#1 Use nmap to test the port and IP address.
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Problem scenario
You cannot ping a server, but your nmap results show that port 22 on the server is open. You can reach the server with nmap, but not with ping. What is wrong?
Possible solution
Is the server in the AWS Security Group that you think it is? Go to the AWS console and verify the security group for the server is what you think is correct.
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Continue reading “Why Cannot You Ping a Server when Nmap Commands to The Server Work?”
Problem scenario
You want to create a Lambda function. What do you do?
Solution
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