How Do You Troubleshoot the Java Program Message “com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: Unknown database foobar”?

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Problem scenario
Your Java program returns this message: “com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: Unknown database foobar”

What should you do?

Possible solution #1
Are you using Amazon Aurora? AWS has a MySQL PaaS offering. You may have a section of the Java code that looks like this:

Connection con=DriverManager.getConnection(“jdbc:mysql://foobar-us-west-2b.abcdefghijk.us-west-2.rds.amazonaws.com:3306/foobar”)

Remove the last “foobar” from the end. The connection string should look like this for Aurora databases:

jdbc:mysql://foobar-us-west-2b.abcdefghijk.us-west-2.rds.amazonaws.com:3306/foobar

Recompile the program.

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In Python, What Are Some Advantages with Calling a Function or as a New Thread?

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Question
Python supports the creation of new threads for [bound or unbound] functions. They can help with multiprocessing. New threads are ideal for non-blocking operations like serving a GUI. If you want a server to begin certain operations in parallel with others, you may want to use new threads as opposed to new processes (which can provide the same parallel processing benefit).

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How Do You Troubleshoot the Message “ERROR: but there is no HDFS_DATANODE_USER defined.”?

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Problem scenarios
One of the following apply to you.

Situation 1:
You run “start-dfs.sh” and it seems to work, but the “jps” command does not show that “DataNode” is running.

OR

Situation 2:
You run “sudo bash start-dfs.sh” but you receive this message:

ERROR: Attempting to operate on hdfs datanode as root
ERROR: but there is no HDFS_DATANODE_USER defined.

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How Do You Troubleshoot Permissions Errors in the /home/ directory of a Linux server?

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Problem scenario
You want to create files in the /home/ directory of your user. You are getting permission errors in the /home/ directory but the permissions are 777 and you are the user who is the owner of the directory, what should you do?

Possible Solution #1

1. Run this command: sudo service autofs stop
2. Make files or directories in home.

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How Do You Determine the IP Address Assignments of Running Docker Containers?

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Problem scenario
You created some Docker containers and assigned them IP addresses. How do you find out what their IP addresses are?

Solution

1. Run this command: docker ps -a # find the container ID of the container you want to know about
2. Run this command but substitute “container_id” with the container ID you found above:
docker inspect -f ‘{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}’ container_id

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In Python, What Are Some Disadvantages with Calling a Function as a New Thread?

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Question
Python supports the creation of new threads for [bound or unbound] functions. They can help with multiprocessing. If you want a server to begin certain operations in parallel with others, you may want to use new processes as opposed to new threads. Both threads and processes can provide the same parallel processing benefit. What are some disadvantages of using a thread to call a function?

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How Do You Set up a Send-Only (Postfix) Email Server on a Linux RHEL AWS Instance?

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Problem scenario
You have a monitoring tool on a RedHat Enterprise Linux server that needs to send out emails upon certain events happening. You want to install and configure an email server. You need to send outbound emails, but you do not need to receive inbound emails. How do you configure RHEL to be able to send out regular emails over the internet?

Prerequisite
This assumes that Postfix has been installed.

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What Are The Kubernetes Concepts “pod label,” “label selector,” and “pod selector”?

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Question
What is the difference between these three two-word terms “pod label,” “label selector,” and “pod selector”?

Answer
This answer provides details on what these are and provides some information on how they are different.

pod label: It is an inherent attribute of the pod. It can be changed via a command like this: kubectl label pod new-podlabel version=5.5 These statements were based on Assistanz.com.

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