目的：下载 docker images 之后，了解 images 内部目录、文件结构，以及容器内部程序运行情况

方法：

1. 使用docker exec (最简单)

和nsenter命令类似，docker exec 命令可以在已经运行的容器运行新的进程（容器必须已经运行才可以，否则会报错），可以运行/bin/bash进入容器：

[arthur@localhost Downloads]$ sudo docker ps
[sudo] password for arthur: 
CONTAINER ID   IMAGE                COMMAND       CREATED       STATUS       PORTS     NAMES
09b6673f175a   hicstuff:v1.0        "/bin/bash"   2 hours ago   Up 2 hours             quizzical_chatelet
c67a7e98646a   koszullab/hicstuff   "/bin/bash"   4 hours ago   Up 4 hours             sleepy_bhabha
[arthur@localhost Downloads]$ sudo docker exec -it  quizzical_chatelet /bin/bash
(base) root@09b6673f175a:/app# pwd
/app
(base) root@09b6673f175a:/app# ls
LICENSE      __init__.py  distance_law.py  io.py     pipeline.py       test_commands.py     test_filter.py    tests
MANIFEST.in  commands.py  filter.py       iteralign.py  requirements.txt  test_digest.py     test_hicstuff.py  version.py
Makefile     cutsite.py   hicstuff       log.py     setup.cfg       test_distance_law.py  test_io.py       view.py
README.md    digest.py      hicstuff.py       main.py     setup.py       test_doctests.py     test_pipeline.py

2. 使用快照（snapshotting）

#查看已经运行的容器,记录要查看容器的 ID 
$ docker ps
#创建新的 images 
$ docker commit  ID  NewImagesName
#通过 `bash` 进入新镜像
$ docker run -it NewImagesName /bin/bash
#删除新的镜像 NewImagesName
$ docker rmi NewIamgesName

3. 使用 ssh

如果需要持续性连接到容器，可以在容器内安装sshd，并运行sshd

#查看 容器 port
$ docker ps
#
$ docker run -d -p PortNumber ContainerName /usr/sbin/sshd -D

4. 使用nsenter

5. 覆盖默认的 ENTRYPOINT

$ docker run --rm -it --entrypoint=/bin/bash NameofImage
#########################################################################
--entrypoint string              Overwrite the default ENTRYPOINT of the image

#覆盖默认 entrypoint  
[arthur@localhost Downloads]$ sudo docker run --rm -it --entrypoint=/bin/bash koszullab/hicstuff  
[sudo] password for arthur: 
(base) root@1f60e1415681:/app# pwd
/app
(base) root@1f60e1415681:/app# ls
LICENSE      __init__.py  distance_law.py  io.py     pipeline.py       test_commands.py     test_filter.py    tests
MANIFEST.in  commands.py  filter.py       iteralign.py  requirements.txt  test_digest.py     test_hicstuff.py  version.py
Makefile     cutsite.py   hicstuff       log.py     setup.cfg       test_distance_law.py  test_io.py       view.py
README.md    digest.py      hicstuff.py       main.py     setup.py       test_doctests.py     test_pipeline.py
(base) root@1f60e1415681:/app# 

#未覆盖
[arthur@localhost Downloads]$ sudo docker run -it koszullab/hicstuff 
[sudo] password for arthur: 
INFO :: generated new fontManager
usage:
    hicstuff [-hv] <command> [<args>...]
[arthur@localhost Downloads]$ sudo docker run -it koszullab/hicstuff  /bin/bash
INFO :: generated new fontManager
Unknown command.
usage:
    hicstuff [-hv] <command> [<args>...]
[arthur@localhost Downloads]$ 
#运行其他 images 
[arthur@localhost Downloads]$ sudo docker run -it hicpro:homo.v1
root@5bf6508e2b7c:/# exit
exit
[arthur@localhost Downloads]$ sudo docker run -it nservant/hicpro:v3.01
root@fb00a89cb150:/# exit
exit
#原镜像运行 commit 之后的
[arthur@localhost Downloads]$ 
[arthur@localhost Downloads]$ sudo docker run -it hicstuff:v1.0 
[sudo] password for arthur: 
(base) root@4de5fd7f7bae:/app# pwd
/app
(base) root@4de5fd7f7bae:/app# ls
LICENSE      __init__.py  distance_law.py  io.py     pipeline.py       test_commands.py     test_filter.py    tests
MANIFEST.in  commands.py  filter.py       iteralign.py  requirements.txt  test_digest.py     test_hicstuff.py  version.py
Makefile     cutsite.py   hicstuff       log.py     setup.cfg       test_distance_law.py  test_io.py       view.py
README.md    digest.py      hicstuff.py       main.py     setup.py       test_doctests.py     test_pipeline.py

拓展：

1. 镜像构建 dockfile 存在差别：

   koszullab/hicstuff 镜像为 from conda ， nservant/hicpro from ubuntu

2. 原镜像 koszullab/hicstuff commit 之后与原镜像的差别：登陆方式出现差别

Reference :
[1] exploring Docker container's file system.stack overflow.