What Is a Shell? A shell is a program that provides an interface between a user and an operating system (OS) kernel. An OS starts a shell for each user when the user logs in or opens a terminal or console window. What Is a Shell Script? A shell script is a file that contains shell and UNIX commands. Similar to compiled executable programs, the shell script has a specific purpose and is reusable. When the commands in the shell script are ordered and error-free, you can execute the shell … [Read more...] about What are Shell Scripts? How to Create Shell Scripts?
DevOps
How to backup and restore Docker containers
The post outlines the steps to take the backup (snapshot) of docker Container and restore it. Please note that this post mainly discusses committing a container as an image. This works on the container that does not use data volume. For containers with data volume, backup of the data volume must be taken separately. Taking backup of Docker Container 1. Commit the required container as an image # docker commit -p [container-id] backup01 sha256:89682d4xxxxxx Now a new image backup01 will … [Read more...] about How to backup and restore Docker containers
Run Docker as a non-root user
The Docker containers by default run with the root privilege and so does the application that runs inside the container. This is another major concern from the security perspective because hackers can gain root access to the Docker host by hacking the application running inside the container. Method 1 - Add user to Docker group 1. To run Docker as a non-root user, you have to add your user to the docker group. 2. Create a docker group if there isn't one: $ sudo groupadd docker 3. Add … [Read more...] about Run Docker as a non-root user
How to Configure Btrfs as the Storage Engine in Docker
Docker is an open platform management tool for Linux Containers. It provides a means for developers and system administrators to build and package applications into lightweight containers. Docker uses devicemapper devices as the default storage engine. To use Btrfs as the storage engine, perform the following steps. Note that Red Hat Enterprise Linux (RHEL) removes the Btrfs storage driver from their build of Docker, both on the Extra Packages for Enterprise Linux (EPEL) repository and the … [Read more...] about How to Configure Btrfs as the Storage Engine in Docker
How to create Docker Image from a Container and Dockerfile
Docker is an open platform management tool for Linux Containers. It provides a means for developers and system administrators to build and package applications into lightweight containers. Docker consists of the following components: Docker Engine – A portable, lightweight runtime and packaging tool Docker Hub – A cloud service for sharing applications and automating workflows Docker is used to create image-based application containers. Image-based containers package an application with … [Read more...] about How to create Docker Image from a Container and Dockerfile
Beginners Guide to The Docker World
Docker: Introduction Docker is an open platform management tool for Linux Containers. It provides a means for developers and system administrators to build and package applications into lightweight containers. Docker consists of the following components: Docker Engine – A portable, lightweight runtime and packaging tool Docker Hub – A cloud service for sharing applications and automating workflows Docker is used to create image-based application containers. Image-based containers … [Read more...] about Beginners Guide to The Docker World
Understanding Positional Parameters (Passing Parameters/Arguments to Shell script)
The execution of scripts is made versatile by the ability to run a script based on arguments supplied on the command line. In this way, the operation of the script varies depending on what arguments are given to the script. The shell automatically assigns special variable names, called positional parameters, to each argument supplied to a script on the command line. The positional parameter names and meanings are shown in Table below. Positional Parameter Name Returns true (0) if: $0The … [Read more...] about Understanding Positional Parameters (Passing Parameters/Arguments to Shell script)
Bash if loop examples (if then fi, if then elif fi, if then else fi)
The if Statement The if statement allows you to specify courses of action to be taken in a shell script, depending on the success or failure of some command. It is a conditional statement that allows a test before performing another statement. The syntax for the simplest form is: if [ condition ] then block_of_statements fi Here, The condition in the if statement often involves a numerical or string test comparison, but it can also be any command that returns a status of 0 when it … [Read more...] about Bash if loop examples (if then fi, if then elif fi, if then else fi)
What is the purpose of .bash_profile file under User Home Directory In Linux
What is the purpose of ~/.bash_profile file Apart from having a home directory to create and store files, users need an environment that gives them access to the tools and resources. When a user logs in to a system, the user’s work environment is determined by the initialization files. These initialization files are defined by the user’s startup shell, which can vary depending on the release. The default initialization files in your home directory enable you to customize your working … [Read more...] about What is the purpose of .bash_profile file under User Home Directory In Linux
Understanding Variables in Bash Shell Under Linux
What are Variables? A variable is a temporary storage area in memory that is either set by the user, shell, system, or any program that loads another program. There are two categories of variables: The environment variables are valid for the duration of the session. The shell variables apply only to the current instance of the shell and are used to set short-term working conditions. Note: When a shell variable follows the dollar $ sign character, the shell interprets that the value … [Read more...] about Understanding Variables in Bash Shell Under Linux