What is meant by shared kernel in Docker?

Question

In Docker ,guest OS share same kernel as Host OS have .

Can someone elaborate more on it.

Let I have centos os which have some kernel version ,when we pull u

Answer 1

Docker was using LinuX Containers (LXC) earlier, but switched to runC (formerly known as libcontainer), that runs in the same operating system as its host. This allows it to share a lot of the host operating system resources. It also uses layered filesystems like AuFS. It also manages the networking for you as well.

AuFS is a layered file system, so you can have a read only part, and a write part, and merge those together. So you could have the common parts of the operating system as read only, which are shared amongst all of your containers, and then give each container its own mount for writing.

So let's say you have a container image that is 1GB in size. If you wanted to use a Full VM, you would need to have 1GB times x number of VMs you want. With LXC and AuFS you can share the bulk of the 1GB and if you have 1000 containers you still might only have a little over 1GB of space for the containers OS, assuming they are all running the same OS image.