How Do You Troubleshoot the Postfix Error “454 4.7.1 jdoe@acme.com: Relay access denied”?

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Problem scenario
You are trying to send an email on a Postfix server. But you keep getting this error: “454 4.7.1 jdoe@acme.com: Relay access denied”

What should you do?

Solution

  1. Back up the /etc/postfix/main.cf file just in case. (This is an optional step.)
  2. Find you server’s internal IP address with a command like this: ip addr show | grep eth0 | grep inet | awk ‘{print $2}’
  3. Modify the /etc/postfix/main.cf file.

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How Do You Troubleshoot Ansible Errors about SELinux?

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Problem scenario
You have Python 3 installed, but you do not have pip3 installed. One of the following also apply to your situation:

Problem scenario #1
You run an Ansible playbook. You receive the error message “Aborting, target uses selinux but python bindings (libselinux-python) aren’t installed.”

Problem scenario #2
You run an Ansible playbook.

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How Do You Get the libselinux-python to Work with Python 3?

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Problem scenario
You have Python 2 and Python 3 installed. When you run Python 3 programs, you get an error message about selinux. The message is consistent with libselinux-python not being installed.

When you enter the Python interpreter for Python 2, you can run this command without errors: import selinux

But when you enter the Python interpreter for Python 3 (e.g., python3), you get errors when you run this command: import selinux

Security of the server is not critical,

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How Do You Troubleshoot the “aws ssm” Command Failing with a Message about “InvalidInstanceId”?

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Problem scenario
In AWS Systems Manager you run an “aws ssm” command. You get “An error occurred (InvalidInstanceId) when calling the Send Command operation.” What should you do?

Solution
Are there spaces or braces inside the double quotes? These symbols are not part of the instance ID. If you are running a script or complex command, extraneous symbols may be getting injected into your instance ID.

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Considerations when Negotiating the Fine Print of an Employment Contract

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Bill Gates’ father was an attorney, and President of the Washington State Bar Association (according to this site). Bill Gates was concerned with the details of contracts in Microsoft’s early days.

I.T. Contractors need to understand American law. To learn about how the contract language works, you may want to hire an attorney. To prepare yourself beforehand, you should try to learn more. If you are an independent contractor who performs software consulting,

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How Do You Troubleshoot the ActiveMQ Build Failure “No plugin found for prefix ‘activemq-perf'”?

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Problem scenario
You run this command:

sudo /opt/maven/bin/mvn activemq-perf:broker -Durl=broker:tcp://localhost:61616

You get this result:

[INFO] Scanning for projects…
Downloading from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-metadata.xml
Downloading from central: https://repo.maven.apache.org/maven2/org/codehaus/mojo/maven-metadata.xml
Downloaded from central: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-metadata.xml (14 kB at 17 kB/s)
Downloaded from central: https://repo.maven.apache.org/maven2/org/codehaus/mojo/maven-metadata.xml (20 kB at 25 kB/s)
[INFO] ————————————————————————
[INFO] BUILD FAILURE
[INFO] ————————————————————————
[INFO] Total time: 1.815 s
[INFO] Finished at: 2020-04-28T15:33:05Z
[INFO] ————————————————————————
[ERROR] No plugin found for prefix ‘activemq-perf’ in the current project and in the plugin groups [org.apache.maven.plugins, …

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How Do You Make an Indefinite Linux Command Go to the Background So That You Have Another Prompt?

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Problem scenario
You want a non-terminating (or hanging) Linux command that never finishes to go to the background. You want to use the next command line prompt. The process starts from a command you issue at the command line. How do you do you get to the next prompt?

Solution

  1. This will suspend the process momentarily. Hold control and tap “z.” Ctrl-z
  1. The above command will result in something like this:
    [555]+ Stopped python3 goodprogram.py

Craft a command like this,

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How Do You Get WordPress Preview Postings to Show “>> Read more…”?

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Problem scenario
You are using WordPress to host your website. Some post previews show a hyperlink “Read more…” but others have no hyperlink. Some post previews (e.g., when you search the website for a pattern) are not updating. Older versions of the post are previewing. How do you get the “Read more…” hyperlink to show in the preview and how do you get the post to be up-to-date?

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