linux kernel - $(uname -a) returning the same in docker host or any docker container

Question

Why $(uname -a) returns the same Linux kernel than the host machine inside a docker container?

uname -a
#=> Linux leo 3.13.0-55-generic #94-Ubuntu SMP Thu Jun 18 00:27:10 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

docker run -ti --rm ubuntu:vivid-20150611 uname -a
#=> Linux 147c3aff216b 3.13.0-55-generic #94-Ubuntu SMP Thu Jun 18 00:27:10 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Even though my host machine is Ubuntu 14.04 (trusty) while the container is Ubuntu 15.04 (vivid) and should have kernel 3.19

Answer 1

Docker uses the host operating system kernel, there is no custom or additional kernel inside the container. All containers running on the machine are sharing this "host" kernel.

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