Docker container not starting with ubuntu image (docker start)

Question

If I run a container directly from an Ubuntu image using docker container run ubuntu, I can easily restart it using a docker start <CONTAINER ID>. However, I run the container using the image by docker run <ID IMAGE>, once I exit the pseudo-terminal, It's completely lost.

I noticed that the status updated every time I tried to restart it, which means that the main process starts and immediately stops. Any idea?

portaivan@training-vm:~$ docker image ls -a
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              latest              d70eaf7277ea        8 days ago          72.9MB
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                      PORTS               NAMES
4004895feff9        d70eaf7277ea        "/bin/bash"         3 hours ago         Exited (0) 3 hours ago                          heuristic_lovelace
3b1b521d62aa        ubuntu              "/bin/bash"         3 hours ago         Exited (0) 23 seconds ago                       sleepy_pike
portaivan@training-vm:~$ docker start 3b1b521d62aa
3b1b521d62aa
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                   PORTS               NAMES
4004895feff9        d70eaf7277ea        "/bin/bash"         3 hours ago         Exited (0) 3 hours ago                       heuristic_lovelace
3b1b521d62aa        ubuntu              "/bin/bash"         3 hours ago         Up 2 seconds                                 sleepy_pike
portaivan@training-vm:~$ docker container start 4004895feff9
4004895feff9
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                     PORTS               NAMES
4004895feff9        d70eaf7277ea        "/bin/bash"         3 hours ago         Exited (0) 2 seconds ago                       heuristic_lovelace
3b1b521d62aa        ubuntu              "/bin/bash"         3 hours ago         Up 17 seconds                                  sleepy_pike
portaivan@training-vm:~$ docker container start -i 4004895feff9
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                     PORTS               NAMES
4004895feff9        d70eaf7277ea        "/bin/bash"         3 hours ago         Exited (0) 2 seconds ago                       heuristic_lovelace
3b1b521d62aa        ubuntu              "/bin/bash"         3 hours ago         Up 28 seconds                                  sleepy_pike

Answer 1

Docker container lives while command is running.
Your command is "/bin/bash".

And that is

pseudo-terminal

So when you closing terminal command (aka container entrypoint) container stops.

• EDIT 1. Nuances explanation

If you run container without -it arguments you start bash without creating session (pseudo-tty).

For example, you can run:

bash -c "echo 'blabla'"

And bash just runs echo command and end process.
So, here is two reasons why container not exited:

1. If you run

docker container run -t --name u_container ubuntu

You will be don't able to input any commands inside container. Because STDIN is not attached. But! You create pseudo-tty by -t parameter and docker container can be started without exiting.

2. With only -i parameter bash don't create tty and want to die as soon as possible. But! docker holds container running and trying to pass input infinitely, even if you not attached to container (see help). Although we can stop bash inserting exit.

-i, --interactive Keep STDIN open even if not attached

So, simple explanation: It depends on how you run shell. As looping and listening pseudo terminal or just as command interpreter. You can compare it with python.
If you run python, it will be python shell. If you run python /script/script.py, python just execute script.py and stops.

Answer 2

After hours and hours, I got it! The problem is the STDIN close at the run of the container. I ran Container 1 and Container 2 using the option -i. I ran Container 3 without the option -i. As you can see in the following image, I was able to start Container 1 and Container 2 but not Container 3.

==== THE REASON! ====

Every process has three data streams (STDIN/ STDOUT/ STDERR). When a process is running in a container, by default the terminal is connected with STDOUT stream of the process running in the container. Hence all the output streams will be visible while running docker run command in the terminal. But if you want to provide input to the running process in the container then you have to connect with STDIN channel of the process which is not by default and is done with docker run -i command.

portaivan@training-vm:~$ docker image ls -a
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
portaivan@training-vm:~$ docker container run -it --name container01 ubuntu
Unable to find image 'ubuntu:latest' locally
latest: Pulling from library/ubuntu
6a5697faee43: Pull complete
ba13d3bc422b: Pull complete
a254829d9e55: Pull complete
Digest: sha256:fff16eea1a8ae92867721d90c59a75652ea66d29c05294e6e2f898704bdb8cf1
Status: Downloaded newer image for ubuntu:latest
root@03b44b790cfa:/# ls
bin  boot  dev  etc  home  lib  lib32  lib64  libx32  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@03b44b790cfa:/# exit
exit
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                     PORTS               NAMES
03b44b790cfa        ubuntu              "/bin/bash"         14 seconds ago      Exited (0) 5 seconds ago                       container01
portaivan@training-vm:~$ docker container start 03b44b790cfa
03b44b790cfa
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
03b44b790cfa        ubuntu              "/bin/bash"         28 seconds ago      Up 2 seconds                            container01
portaivan@training-vm:~$ docker image ls -a
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
ubuntu              latest              d70eaf7277ea        8 days ago          72.9MB
portaivan@training-vm:~$ docker container run -it --name container02 d70eaf7277ea
root@e6123c0bbe81:/# ls
bin  boot  dev  etc  home  lib  lib32  lib64  libx32  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@e6123c0bbe81:/# exit
exit
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS                     PORTS               NAMES
e6123c0bbe81        d70eaf7277ea        "/bin/bash"         10 seconds ago       Exited (0) 3 seconds ago                       container02
03b44b790cfa        ubuntu              "/bin/bash"         About a minute ago   Up About a minute                              container01
portaivan@training-vm:~$ docker container start e6123c0bbe81
e6123c0bbe81
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS              PORTS               NAMES
e6123c0bbe81        d70eaf7277ea        "/bin/bash"         22 seconds ago       Up 2 seconds                            container02
03b44b790cfa        ubuntu              "/bin/bash"         About a minute ago   Up About a minute                       container01
portaivan@training-vm:~$ docker container run --name container03 d70eaf7277ea
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                     PORTS               NAMES
7adbb0089b56        d70eaf7277ea        "/bin/bash"         3 seconds ago       Exited (0) 2 seconds ago                       container03
e6123c0bbe81        d70eaf7277ea        "/bin/bash"         2 minutes ago       Up About a minute                              container02
03b44b790cfa        ubuntu              "/bin/bash"         3 minutes ago       Up 2 minutes                                   container01
portaivan@training-vm:~$ docker container start 7adbb0089b56
7adbb0089b56
portaivan@training-vm:~$ docker container ls -a
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS                     PORTS               NAMES
7adbb0089b56        d70eaf7277ea        "/bin/bash"         15 seconds ago      Exited (0) 2 seconds ago                       container03
e6123c0bbe81        d70eaf7277ea        "/bin/bash"         2 minutes ago       Up About a minute                              container02
03b44b790cfa        ubuntu              "/bin/bash"         3 minutes ago       Up 3 minutes                                   container01
portaivan@training-vm:~$

REFERENCES

https://docs-stage.docker.com/engine/reference/commandline/container_run/ https://www.howtogeek.com/435903/what-are-stdin-stdout-and-stderr-on-linux/