What is a Docker image
To simply understand, a Docker image is a Linux file system (Root FileSystem), which contains Programs and corresponding data that can run in the Linux kernel.
Speaking of this, we may need to add some knowledge related to the Linux operating system:
Generally speaking, Linux is divided into two parts: Linux Kernel (Linux Kernel) and user space , and the real Linux operating system refers to the Linux kernel. Our commonly used operating systems such as Ubuntu and CentOS are actually distribution versions (Linux Distribution) formed by different manufacturers adding their own software and tools (tools) based on the Linux kernel.
Therefore, we can also think of the image as the user space mentioned above. When Docker creates a container through the image, the user space defined by the image is run on the host as an independent and isolated process. On top of the Linux kernel.
Here we want to emphasize two characteristics of mirroring:
1. Mirroring is layered: that is, a mirror can be composed of multiple intermediate layers, and multiple mirrors can share the same intermediate layer. Layers, we can also generate a new image by adding one more layer to the image.
2. The image is read-only: After the image is built, it cannot be modified. What we said above is to add a layer to build a new image. This is actually done through Create a temporary container, add or delete files on the container to form a new image, because the container can be changed dynamically.
What is a warehouse
The warehouse (Repository) is a place where images are stored centrally. There is a concept that needs to be distinguished here, that is, the warehouse and the warehouse server (Registry) are They are two different things. For example, Docker Hub is a warehouse server officially provided by Docker, but sometimes we don't need to distinguish these two concepts too much.
Recommended tutorial: docker tutorial
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