A Technical I.T./DevOps Blog
Problem scenario
You are using Postfix. You are trying to send emails directly from the Postfix server. After you use telnet and helo commands, you enter a recipient like this:
rcpt to: johndoe@example.com
But you get this error:
“550 5.1.1 johndoe@example.com: Recipient address rejected: User unknown in local recipient table”
What should you do?
Root cause
If you change the /etc/postfix/main.cf file to have emails use a “reply-to” of example.com,
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Question
AWS’s Five Pillars of Well-Architected Framework recommend monitoring as a component of three of the pillars (operational excellence, reliability and performance efficiency).
There is no question that monitoring is important inside or outside of a public cloud. What patterns or traits might a good centralized monitoring system have (consistent with some phrase as “best practices”)?
Answer
Here are 15 characteristics of good monitoring.
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Continue reading “What Are the Recommended Practices of Monitoring?”
Problem scenario
You want to send more than one line of text as the body of an email. You want to use the command prompt of a RedHat Enterprise Linux server.
Solution
Prerequisites
You have installed mailx. If you need to do this, run this command: sudo yum -y install mailx
Procedures
1.
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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 want Linux to send out an email with a alias email address in the “From” field. You are using the mail command on a Linux server. You want to customize the “from” address in the emails that you send. What do you do to choose your own “from” email address (e.g., jdoe@myowndomain.com) in the email that is sent out?
Solution
Prerequisites
You need to have mailx installed.
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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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Problem scenario
You have some .eml files (e.g., emails from a web-based email account) that you want to view. How do you display them for free?
Solution
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Problem scenario
You have a web-based email provider. You want to save all of your emails in one location quickly. How do you download them into one file?
Solution
If there are maximum size limits for sending a single email (e.g., 25 MB), this method may not work if all of your emails put together exceed this size limit.*
1.
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Problem scenario
You want to do deploy (install and configure) GitLab on a Debian Linux server. What do you do?
Solution
1. Get a Debian or Ubuntu Linux server with either 3.5 GB of RAM or at least 1.5 GB of RAM and 2 GB of virtual memory. If you need to resize an AWS instance, see this posting. If you need to resize a GCP instance,
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Continue reading “How Do You Install GitLab on Debian or Ubuntu Linux?”