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Layers that build an Image


#1

Hi,

Please clarify the following when storage driver is overlay

  • Layers information given by docker image inspect <image name/id>

  • Layers information given in docker history <image name/id>

  • the contents of /var/lib/docker/image/overlay/layerdb/sha256

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The following are the reference prints:

[root@eilagcy1 image]# docker info | grep -i storage

WARNING: overlay: the backing xfs filesystem is formatted without d_type support, which leads to incorrect behavior.

Reformat the filesystem with ftype=1 to enable d_type support.

Running without d_type support will not be supported in future releases.

Storage Driver: overlay

[root@eilagcy1 image]#

From the above print, it is clear that the storage driver is overlay

[root@eilagcy1 image]# docker image pull nginx:latest

latest: Pulling from library/nginx

a5a6f2f73cd8: Pull complete

1ba02017c4b2: Pull complete

33b176c904de: Pull complete

Digest: sha256:5d32f60db294b5deb55d078cd4feb410ad88e6fe77500c87d3970eca97f54dba

Status: Downloaded newer image for nginx:latest

[root@eilagcy1 image]#

From the above, we can see the nginx is comprised of the following 3 layers

a5a6f2f73cd8

1ba02017c4b2

33b176c904de

[root@eilagcy1 sha256]# docker images

REPOSITORY TAG IMAGE ID CREATED SIZE

nginx latest 568c4670fa80 7 days ago 109MB

[root@eilagcy1 sha256]# docker image inspect 568c4670fa80 | grep -A6 Layers

“Layers”: [

“sha256:ef68f6734aa485edf13a8509fe60e4272428deaf63f446a441b79d47fc5d17d3”,

“sha256:ad5345cbb119f7c720123e3adf28b164143e4157ca6e46a629ca694e75f7825f”,

“sha256:ece4f9fdef598687f23d39643bacbf2c609201b087b93bbae81b931da72d2a64”

]

}

}

Docker inspect on this image i.e 568c4670fa80 shows some different names of layers ???

The /var/lib/docker shows some different layer names???

[root@eilagcy1 sha256]# pwd

/var/lib/docker/image/overlay/layerdb/sha256

[root@eilagcy1 sha256]# ls -l

total 0

drwx------. 2 root root 80 Dec 5 09:23 6b9d35d8d75115937cd78da275f527cccef672cbd71f34062dffe2e930fd7e13

drwx------. 2 root root 80 Dec 5 09:23 ac0442c0fafd48e24a96fa3099ea7ad20012c8759e1dd03dd387dbfbe382984c

drwx------. 2 root root 67 Dec 5 09:23 ef68f6734aa485edf13a8509fe60e4272428deaf63f446a441b79d47fc5d17d3

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Regards,
Anuraag