A Technical I.T./DevOps Blog
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:
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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, install Apache web server.
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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.
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Continue reading “How Do You Write a Java Program to Read in Letters and Numbers?”
Question
In Python you are familiar with importing the os module and using different exec variations. What are some reasons that you would not use os.execlp?
Answer
1. If you use os.execlp to call another program, that program is more likely to return “Killed”. The resources of the child process are, by default, more limited in part because the fork operation is expensive from a system’s resources perspective.
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Continue reading “In Python, What Are Some Disadvantages to Using os.execlp to Fork a Process?”
Problem scenario
You have installed Java. But you cannot use the javac command. You get errors like this: “-bash: javac: command not found”
How do you install Java so you can compile programs on a RedHat Linux server?
Solution
Run this command: sudo yum -y install java-devel
If you want to do this on a Debian or Ubuntu Linux server,
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Continue reading “How Do You Install Java so You Can Compile Programs on a RHEL Server?”
Problem scenario
You mounted 2 GB of swap space (virtual memory) called 2GB.swap. (You followed these directions. Later you added RAM to the server.) This 2 GB swap space is still mounted. How do you clear it and repurpose it on your hard drive?
Solution
1. Run this command: sudo swapoff -a
2. Modify the /etc/sysctl.conf file. (You may want to back it up before you make a change.) Here is what you need to do to change it:
Run this command: sudo vi /etc/sysctl.conf
# eliminate the “vm.swappiness=10” stanza
3.
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Continue reading “How Do You Reclaim Swap Space on a Linux Server?”
Problem scenario
You recently connected a jumper connector to two GPIO pins accidentally on your Raspberry Pi. Now your Raspberry Pi will not start, and it seems fried. There is a red light that is on. There is no flashing light and no green light. There is no output to the monitor. You are not sure if the Raspberry Pi is wasted.
Solution
1.
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