A Technical I.T./DevOps Blog
Problem scenario
You are using a Red Hat derivative of Linux (e.g., CentOS/RHEL/Fedora). When trying to run a mongod command you receive this message: “/usr/bin/mongodb/bin/mongod: error while loading shared libraries: libcrypto.so.1.0.0: cannot open shared object file: No such file or directory”.
What should you do?
Solution
Get different installation media. If you try to install a .tgz file for Ubuntu on CentOS/RHEL/Fedora, you will get this message.
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Problem scenario
Your C program compiles. But you get the error “Segmentation fault.” You expect the value of a variable to be printed. How do you get the value to be printed without this error?
Solution
Does every print function print? If one print function seems to be displaying the “Segmentation fault” error, look closely at the syntax thereof. Here is a line that will produce this error:
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Problem scenario
The command “git push origin master” hangs. What should you do?
Solution
Cancel the job with ctrl-c. (Hold the “Control” key and tap the “C” key.)
For the target .git repository, does the file have the owner and group associated with the “git” user?
If you used the git user in the “git clone” command (as in “git clone @…”) but then changed the owner and group of the .git repository to something else,
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Question
Can the kernel, or code running in it, access hardware directly?
Answer
Yes.
kernelspace lives in RAM (or memory) (1). Code that is processing in kernelspace can fully access other processes in memory or fully access hardware directly (1).
The kernel governs hardware utilization via drivers, memory, disk space, memory and CPU (1).
In RedHat distributions of Linux (including CentOS and Fedora) userspace exists in RAM (or memory) (2).
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Problem scenario
You have a Python list with n items. You are getting a “IndexError: pop index out of range” error. The order that these lists are being printed (used or displayed) is not what you expect. Your program prints the entire list initially, so you know what to expect. This IndexError and the order of the items being displayed is not what you expect. Here is an example:
print(fun_list)
[‘item1’,
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Continue reading “How Do You Deal with the Python Error “IndexError: pop index out of range”?”
Problem scenario
You use start-dfs.sh and start-yarn.sh and there are no errors. They seem to work, but when you use the jps command, you do not see the service you expect. Why isn’t a jps process starting when you run one of these scripts?
Solution
The root cause could be a variety of root causes. Here are some potential solutions.
1. In these files,
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Continue reading “How Do You Get hdfs or Yarn to Start the Jps Process You Expect to Start?”
Problem scenario
You have a web server with an external IP address (e.g., a VPS, an EC-2 instance, a DigitalOcean droplet, a VM in Azure or GCP). You have a domain name, e.g., funexample.com, that you have registered. You want to go to craft a URL foobar.funexample.com to resolve to this web server with an external IP address. Right now when you open a web browser and go to foobar.funexample.com,
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Continue reading “How Do You Use Amazon Route 53 with a Domain Name?”
Problem scenario
You are familiar with codebases in the context of configuration management or version control. How can you invoke “git rebase” to learn more about git?
Solution
If you use the man page for “git rebase” you see this phrase to define “git rebase”: “Forward-port local commits to the updated upstream head”
What does “Forward-port local commits to the updated upstream head” mean?
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Updated on 1/22/19
Problem scenario
You installed Graylog in a Docker container. You open the URL for the server in a web browser. You see this message:
” Server currently unavailable
We are experiencing problems connecting to the Graylog server running on http://127.0.0.1:9000/api. Please verify that the server is healthy and working correctly.
You will be automatically redirected to the previous page once we can connect to the server.
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Problem scenario
You have a variable in a Bash script that helps you compose a new Bash command. You want to create a complex and dynamic Bash command. This variable includes one or more spaces in it.
You can echo the commands and verify that these are valid Linux commands. You run them and they test out. But to run automatically in a script, you are finding that it can be difficult.
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