The while loop allows you to repeatedly execute a group of statements while a command executes successfully. The syntax for the while loop is: while control_command do statement1 ... statementN done where, control_command can be any command that exits with a success or failure status. The statements in the body of the while loop can be any utility commands, user programs, shell scripts, or shell statements. When a while statement is executed, the … [Read more...] about “while” Loop Examples in Shell Scripts
DevOps
How to Configure Network Namespaces in Docker Containers
This post tells how Docker uses network namespace to isolate resources. The following figure is the lab setup to help you understand the steps visually: 1. Create two network namespaces: ns1 and ns2. - Add two new naetwork namespaces: # ip netns add ns1 # ip netns add ns2 The above commands create network space by passing a flag to the clone() system call, CLONE_NEWNT. - Check the new created ns: # ip netns list ns2 ns1 When the IP tool creates a network namespace, it … [Read more...] about How to Configure Network Namespaces in Docker Containers
How to change the default IP address of docker bridge
Question: what is the proper procedure to reconfigure the docker interface to use an address range (e.g., > 172.200) for the virtual interfaces it uses? You can reconfigure the default bridge network by providing the bip option along with the desired subnet in the daemon.json (default location at /etc/docker/daemon.json ) file as follows: # vi /etc/docker/daemon.json { "bip": "172.200.0.1/16" } Then restart the docker daemon as root. On CentOS/RHEL 6 use the service command to … [Read more...] about How to change the default IP address of docker bridge
“su: Authentication failure” – in Docker
The Problem In some situations, a normal user within a Docker container cannot run 'su' command to switch user. When 'su' command is issued, the following error returns. $ su - Password: [entering correct password] su: Authentication failure The Solution The sticky permission may be missing in /usr/bin/su within the container. With root privilege, you may fix as follows: 1. First check the current permissions for the /usr/bin/su binary file. # ls -l /usr/bin/su -rwxr-xr-x 1 root … [Read more...] about “su: Authentication failure” – in Docker
How to Pause and Resume Docker Containers
Question: How to Pause and Resume running containers on docker host? This post will help to know about pausing and resuming any running containers on the Docker host. Let's first start the docker container "memory_test" on the docker host. # docker start memory_test memory_test To stop the pause the docker container: # docker pause memory_test memory_test Verify the state of docker container using "docker ps": # docker ps CONTAINER ID IMAGE COMMAND … [Read more...] about How to Pause and Resume Docker Containers
How to find docker storage device and its size (device mapper storage driver)
Question: How to find the running docker storage device when docker is using the device-mapper storage driver and then check the size of it? 1. Please run the "docker info" command to display docker system-wide information which contains the docker storage info. # docker info Containers: 0 Running: 0 Paused: 0 Stopped: 0 Images: 0 Server Version: 18.03.1-ol Storage Driver: devicemapper Pool Name: docker-251:0-102683530-pool Pool Blocksize: 65.54kB Base Device Size: … [Read more...] about How to find docker storage device and its size (device mapper storage driver)
Understanding “docker stats” Command Output
Question: How to monitor a running docker container performance metrics. For example, CPU,memory, I/O and network stats? The docker stats command can continuously report the basic CPU, memory, network and disk I/O metrics. For example: # docker stats a3f78cb32a8e CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS a3f78cb32a8e hello-world 0.00% 2.137MiB / 3.605GiB 0.06% 0B / 0B 9.95MB / 0B 0 Alternatively, you can … [Read more...] about Understanding “docker stats” Command Output
‘docker images’ command error – “Permission Denied”
The Problem A regular user is not able list images using docker images command. Following error can be observed. user01> docker images Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.27/images/json: dial unix /var/run/docker.sock: connect: permission denied The Solution User is not part of docker group and doesn't have permissions to execute docker related commands. Add regular user to … [Read more...] about ‘docker images’ command error – “Permission Denied”
Docker Basics – Expose ports, port binding and docker link
This post illustrates three methods to link Docker containers. Expose ports and port binding Expose ports This method is used for within the same network or the docker host. Containers on the same network can talk to each other over their exposed ports and you can expose the ports by one of the below methods. - Put EXPOSE 80 (or any port you want) in your Dockerfile that’s going to tell Docker that your container’s service can be connected to on port 80. - Expose a port using '--expose … [Read more...] about Docker Basics – Expose ports, port binding and docker link
How to Disable Docker Process and docker0 Interface on CentOS/RHEL
When the docker packages are installed, the services and related docker0 network interface are enabled. In some cases, you may want to disable the docker service and the docker0 network interface as well. This post details how to disable Docker and the docker0 interface if it is not required or if the docker0 interface is conflicting with other network interfaces/routes. 1. Ensure the Docker service is stopped: # service docker stop # for CentOS/RHEL 6 # systemctl stop docker # … [Read more...] about How to Disable Docker Process and docker0 Interface on CentOS/RHEL