"No command specified" from re-imported docker image/container

english
#1

I am trying to take a docker container from one machine and run it on another and encountering this error: "Error response from daemon: No command specified".

Below is a simplified example showing the problem:

docker --version
Docker version 1.10.1, build 9e83765
docker pull ubuntu
docker run --name u1 -dit ubuntu:latest
docker export -o exported u1
docker stop u1
docker rm u1
docker import exported ubuntu:imported
docker run --name u1 -dit ubuntu:imported
docker: Error response from daemon: No command specified.

In that example, we first pull an image (ubuntu) and successfully create/run container u1 from it. Then we export that container to a file (exported), stop/remove the container, import the file into a new image (ubuntu:imported) and try to run a new container from it. It fails.

#2

docker export does not export everything about the container — just the filesystem. So, when importing the dump back into a new docker image, additional flags need to be specified to recreate the context.

For example, if the original container was running fine because the Dockerfile that was used for creating its image had CMD ["/usr/bin/supervisord"] in it, then import your dump this way:

docker import \
--change 'CMD ["/usr/bin/supervisord"]' \
path/to/dump.tar imagename:tagname
#3

you can use docker load command to load images from archive file . this command will import image file and args together.

#4

Got this error when trying to export and import docker microsoft/mssql-server-linux.

https://hub.docker.com/r/microsoft/mssql-server-linux/

Commands to export and import:

docker export --output "C:\Users\oscar\Desktop\sqlTestMS.tar" msSQL

docker import "C:\Users\oscar\Desktop\sqlTestMS.tar" mssql

However we could not find the command to run it. The solution was listing all containers on the exporting machine and looking at the command ran.

docker ps

enter image description here

From there we could find out how to run the correct command:

docker run --name msSQL -p 1401:1433 -d mssql:latest /opt/mssql/bin/sqlservr
#5

When you export a container it lost own history which contains image layers and meta data. So your container lost its pid states.

Every container should have a initial (root) process. You are overiding the default entrypoint on the dockerfile as bash. [edited] I think even you dont override it uses default , not defined in ubuntu base image. So you should start your initial process with cmd command. I think there is no bug. It is a dockerfile feature for reusablity.

#6

if using import 

docker save nginx:alpine | ssh rmeote-host docker import -
sha256:f6098fc18511abbbfe9e52ed0d0ccc1fbe4f7b018ee1cd85392999aa92ebba1b


we see errors


docker container run -d -p 2020:80  nginx:alpine

docker: Error response from daemon: No command specified.

See ‘docker run --help’.

if using load 

docker save nginx:alpine | ssh remote-host "cat - | docker load"
Loaded image: nginx:alpine

docker container run --name nginx -dp 2020:80 nginx:alpine

7cc8836bef1e276f8aa986a09186e9e227542be3b094b082b9ab1f6d3c290a99

docker ps

CONTAINER ID   IMAGE          COMMAND                  CREATED         STATUS        PORTS                                   NAMES

7cc8836bef1e   nginx:alpine   "/docker-entrypoint.…"   2 seconds ago   Up 1 second   0.0.0.0:2020->80/tcp, :::2020->80/tcp   nginx

#7

Got it working with these additional steps:

  1. Create Dockerfile as follows:

    FROM ubuntu:imported
ENTRYPOINT bash

  2. Build new image:

    docker build -t ubuntu:importedwithdockerfile .

  3. Now it will run:

    docker run --name u1 -dit ubuntu:importedwithdockerfile

However, it is still unclear why simply exported and then imported image does not work right away. Is this a bug?