A Technical I.T./DevOps Blog
Goal: You want two Docker containers to use the same file share on the Docker server from time to time.
Problem/Error blocking goal: In a Docker container, when you try to change directories to a directory that is on the Docker host (e.g., the docker container was created with the –volume flag), and you get an error “bash: cd <directoryname> permission denied,” you have to run two commands to fix it.
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Continue reading “Having Two Docker Containers Share A Directory on the Host”
Normally you can enter a Docker container with this command:
docker exec -it <containerIDbash
It is possible you receive an error that says ‘exec “bash”: executable file not found in $PATH’
The root cause could be related to insufficient disk space on the Docker host. Delete files or otherwise make room (e.g., add disk space). Then stop the container with this command: docker stop <containerID
Finally,
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Problem: When trying to use yum commands with a repository on your network, you receive “Failed to connect to x.x.x.x:80; Connection refused” (where x.x.x.x is the IP address of the yum repository server). What are some possible solutions to this problem?
Potential solutions:
1) Verify the Linux server with the repository has a valid repository created. Use “createrepo <directoryToRPMfiles>”
2)
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Goal: To have Apache start when a Docker container starts running do the following (for Docker containers based on RHEL/CentOS/Fedora).
Prerequisite: The Docker container was created with the “-p 80:80” flag. Other port numbers besides 80 will work. The port numbers do not have to be the same. They can be any number between 1 and 65535. If there is no binding of the Docker host’s TCP ports to the container,
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Create the Docker Container with this:
docker run -i -v /absolute/path/on/DockerHost:/absolute/path/in/Docker/Container -t repositoryName /bin/bash
where “/absolute/path/on/DockerHost” is the path and directory on the Docker server that will be presented to the Docker container in the location of “/absolute/path/in/Docker/Container.”
The “repositoryName” in the example is found by running this command: docker images
In the results of this command under the left-hand column are the potential repositoryName values.
Be advised that the /absolute/path/in/Docker/Container will have its contents obliterated when the Docker container is created.
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Continue reading “How A Docker Container and Its Server Can Share a Directory”
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”