A Technical I.T./DevOps Blog
Run these commands (with sudo in front of them or, less preferably, as the root user):
1) fdisk -l > /tmp/saveOfOutput # This creates a baseline for step #3 below.
2) With a physical server: Turn off the server and connect the physical disk, and turn it back on.
With a virtual server: Add the disk in vSphere
3) As root, issue these commands:
fdisk -l #find added device in the output of this command
#If it is not seen,
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Continue reading “How To Add a Disk To a RHEL/CentOS/Fedora Server”
Some online Docker literature suggests creating a new Docker container (e.g., the “docker run” command) with these two options:
–net=host –privileged=true
There are some caveats with these flags. First, if you use them, within your container you can make changes to the Docker server itself.* For some applications, this defeats Docker’s purpose. Secondly, if the application you run in Docker becomes compromised, the entire host could be vulnerable to an attack through the Docker container.*
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Continue reading “Concerns About Creating a Docker Container With Optional Flags”
Q. How do you create a yum repository server on a network?
Answer:
1. Put the .rpm files into a directory (e.g., /mnt/coolrepo).
2. Enter this command: createrepo /mnt/coolrepo
3.
a) Install Apache.
b) Configure the httpd.conf file to make the /mnt/coolrepo file presentable over the network.
cd /; find . -name httpd.conf
vi httpd.conf
Edit the DocumentRoot stanza to have the value be /mnt/coolrepo
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Continue reading “Five Steps To Creating a Yum Repository Available on Your Network”
First, find the Docker container ID. Issue this:
docker ps -l
The results of the above command should provide the container ID. Next issue this:
docker inspect <containerID
For greater detail, see this posting.
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Continue reading “How To Find the IP Address of a Docker Container”
#1 When updating firewalld with the firewall-cmd command, remember that a response of “success” does not mean the changes took effect. You still have to stop and restart the services. There are three ways of doing this: reboot the server, use systemctl stop firewalld; systemctl start firewalld, firewall-cmd –reload
#2 When trying to install an rpm package (e.g., rpm -ivh nameOfNewPackage), you can get this error:
“…existingPackageName is obsoleted by nameOfNewPackage…”
One solution to this is to uninstall the existingPackageName.
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Continue reading “Linux (RedHat distribution) Administration Tips”
Some critics say that Ansible does not do enough to warrant its deployment in an enterprise. The initial deployment to the managed nodes is less than what Puppet and Chef require. Even minionless deployments of SaltStack require more configuration work than Ansible. In this post, we want to demonstrate an advantage of adopting Ansible related to the first deployment. When using passwordless SSH authentication, the great benefit is the lack of a prompt. But experienced I.T.
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Docker is itself a dependency resolution tool. It is a container that allows a DevOps engineer to prepare one-time an OS environment with nuanced dependencies and configurations for other packages to be installed.
Leveraging the efficiency of a configuration management tool (such as Ansible, CFEngine, Chef, Puppet, and SaltStack) can empower DevOps engineering. It can also necessitate using duplicative deployments in different environments (development, quality assurance, staging, and production). Having a backup plan for disaster recovery is also important.
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Continue reading “How Do You Copy Files into a Docker Container from the Server’s Command Line?”
I edited Wikipedia’s OpenStack Article found here. This is the paragraph for Sahara as I found it on 4/5/16:
“Sahara aims to provide users with simple means to provision Hadoop clusters by specifying several parameters like Hadoop version, cluster topology, nodes hardware details and a few more. After a user fills all the parameters, Sahara deploys the cluster in a few minutes. Sahara also provides means to scale an already-provisioned cluster by adding and removing worker nodes on demand.”
This is what I revised it to be:
“Sahara is a component to easily and rapidly provision Hadoop clusters.
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Continue reading “OpenStack Wikipedia Article: Sahara Paragraph Updated”
To see if Docker has started, do this command:
ps -ef | grep -i docker
If that returns only a service for the grep itself, then Docker is not running. Occasionally the Docker service won’t start through traditional methods. But some users have found that this command will work reliably:
docker daemon &
The “&” allows for the next prompt to return. This method is explicit to new users of Docker too.
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Continue reading “How to Handle “Failed to connect to the Docker daemon” message in Linux”
Question: How do you solve circular dependency problems when installing RPMs in RedHat Linux?
Problem Scenario: For example, you keep trying to install different RPMs, but they always require a different installation. By exhaustively going through the dependencies, you find a circle of dependencies. This is sometimes called mutual recursion.
Root cause: Human error.
Solution: The way to resolve circular dependencies is with a yum localinstall command with a list of each of the RPM packages afterward.
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Continue reading “How do you install two or more RPM packages when they depend on each other?”