ssh Connection reset by 192.168.x.x

Question

I'm trying to ssh login from Mac OSX 10.10 into CentOS 7.1 on boot2docker by using public key authentication. The problem is that ssh shows Connection reset by 192.168.99.100 when I login to CentOs (192.168.99.100 is the container's IP address). Here is my Dockerfile for building CentOS image:

FROM centos:centos7
MAINTAINER moutend <[email protected]>

RUN yum -y update; yum clean all
RUN yum -y install openssh-server

RUN mkdir /var/run/sshd
RUN sed -i 's/^#PermitRootLogin yes/PermitRootLogin no/' /etc/ssh/sshd_config
RUN sed -i 's/^PasswordAuthentication yes/PasswordAuthentication no/' /etc/ssh/sshd_config
ADD id_ecdsa.pub /home/moutend/.ssh/authorized_keys

RUN adduser -g wheel moutend
RUN echo moutend:foobarfoobar | chpasswd
RUN chown -R moutend:wheel /home/moutend
RUN chmod 600 /home/moutend/.ssh/authorized_keys

EXPOSE 22
CMD ["/usr/sbin/sshd", "-D"]

The following commands are I did.

# On Mac OSX
ssh-keygen -t ecdsa
docker-machine create -d virtualbox dev
docker-machine scp myDockerfile id_ecdsa.pub dev:
docker-machine ssh dev # Login to boot2docker

# On boot2docker
docker build -t test -f myDockerfile .
docker run -d -P test
docker port `docker ps -lq` # Get the port for ssh

And then I got the error message below:

ssh-add id_ecdsa
ssh moutend@`docker-machine ip dev` -p 32772
Connection reset by 192.168.99.100

Ofcourse the port number is correct. So I don't know why connection reset happens. How can I solve this?

Solution

The first thing to try is increase the verbosity of ssh by adding -v:

ssh -v moutend@`docker-machine ip dev` -p 32772

that will give you extra debugging information.

If that doesn't help, and assuming you used docker run --name sshtest -d -P test to name the container sshtest;

docker logs sshtest

to see if sshd is (still) running. (This will show that the /etc/ssh/ssh_host_ed25519_key host ssh keys are missing, and you have to run ssh-keygen -A once to generate those host keys in /etc/ssh/)

If it were still running you can check the setup of the inside for correctness by exec-ing into the the container:

docker exec -it sshtest /bin/bash

Of course using docker exec eliminates the need for running sshd in a lot of containers in the first place.

You can also look at what others have done in similar setups (if you haven't already e.g. this setup

Comments

[Jakuje]

make sure that also ~/.ssh directory has proper permissions. Running the server in debug mode (-ddd) might also give some clue.

[moutend]

@Jakuje Thanks. However ~/.ssh directory is mode 700. It's proper permission.

[moutend]

docker logs shows Could not load host key: /etc/ssh/ssh_host_ed25519_key. So I put RUN ssh-keygen -A into my Dockerfile, everything works fine and I can login to the container by using public key authentication. Thank you for giving me many advices!

[Anthon]

@moutend I updated my answer with that info (so future visitors don't have to read all the way down to the comments). Consider accepting my answer (clicking the V next to it) if it solves your problem, that is the way people seeing your question on this site, know it has a working answer.