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,
…
Problem scenario
You want to print three integers. You do not want to convert them to be part of a string. You want a space to separate each integer. How do you do this in Python?
Solution
Assuming your variables are x, y, and z, and they are integers, use a line like this:
print(x, y, z)
Here is a complete program that proves it works:
x = 5
y = 3
z = 100
print(x, …
Continue reading “In Python How Do You Print Three Integers Separated by a Space on the Same Line?”
Problem scenario
You want to download pictures (e.g., .png, .jpeg etc.) from websites. How do you use Python to download such files?
Solution
Use this program with a subdirectory in the directory that this program resides to receive the picture files.
“””
dwldimages.py
Downloads all the images on the supplied URL, and saves them to the
specified output file (“/test/” by default)
Usage:
python dwldimages.py http://example.com/ /tmp/test/ # where /tmp/test/ is the directory you want to save the image files to. …
Continue reading “How Do You Write a Python Program to Download the Images of a Website?”
Problem scenario
A Groovy program is returning an incorrect value for an integer variable. What is wrong?
Possible solution #1
Check the logic of your program. Use the println command to see the earliest point when this variable is assigned an incorrect value. This helps you pinpoint the problem.
Possible solution #2
Is the variable being assigned a number in quotes like this?
…
Continue reading “How Do You Assign a Variable in Groovy to Be an Integer Value?”
Problem scenario
In AWS you manually added a Security Group rule for the source of a given IP address. This IP address is either the internal or external IP address. You can ping one of them (either the internal or external IP address). Why cannot you ping each IP address?
Solution
Check to see if a firewall is running on the Linux server.
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Problem scenario
You want to run an Ansible playbook to push configuration changes down (e.g., transfer files to managed nodes). How do you do this?
Solution
Prerequisites
This assumes that you have set up Ansible. If you need directions for deploying an Ansible control server, see this posting. If you need directions for deploying a managed node after the central Ansible server has been set up,
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Problem scenario
You run hostname -f and you get this error: “hostname: Name or service not known”
How do you solve this problem?
Solution
Do these things in this order:
…
Continue reading “How Do You Solve the Linux Error “hostname: Name or service not known”?”
Problem scenario
You deployed Apache Mesos. The web UI is having problems. You see the error “Failed to connect to x.x.x.x:5050.” What should you do?
Solution
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Problem scenario
You want a REST API endpoint. How do you create a URL that is a proof-of-concept to trigger a Python program?
Solution
Prerequisites
i. You have installed Python 3. If you are using CentOS/RHEL/Fedora, run this: sudo yum -y install python3
ii. You need a web server installed. If you do not have one,
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Problem scenario
You want to create a basic Java program that can read alphanumeric input interactively. How do you write such a program?
Solution
1. Verify the “javac” command works. Run “man javac” to see the man page. If you do not get a man page, install the Java development tools. On a RedHat derivative, run this: sudo yum -y install java-devel
2.
…
Continue reading “How Do You Write a Java Program to Read in Letters and Numbers?”