How do I get into a Docker container's shell?

docker attach will let you connect to your Docker container, but this isn't really the same thing as ssh. If your container is running a webserver, for example, docker attach will probably connect you to the stdout of the web server process. It won't necessarily give you a shell.

The docker exec command is probably what you are looking for; this will let you run arbitrary commands inside an existing container. For example:

docker exec -it <mycontainer> bash

Of course, whatever command you are running must exist in the container filesystem.

In the above command <mycontainer> is the name or ID of the target container. It doesn't matter whether or not you're using docker compose; just run docker ps and use either the ID (a hexadecimal string displayed in the first column) or the name (displayed in the final column). E.g., given:

$ docker ps
d2d4a89aaee9        larsks/mini-httpd   "mini_httpd -d /cont   7 days ago          Up 7 days                               web                 

I can run:

$ docker exec -it web ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
18: eth0: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP 
    link/ether 02:42:ac:11:00:03 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.3/16 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:acff:fe11:3/64 scope link 
       valid_lft forever preferred_lft forever

I could accomplish the same thing by running:

$ docker exec -it d2d4a89aaee9 ip addr

Similarly, I could start a shell in the container;

$ docker exec -it web sh
/ # echo This is inside the container.
This is inside the container.
/ # exit
$

To bash into a running container, type this:

docker exec -t -i container_name /bin/bash

or

docker exec -ti container_name /bin/bash

or

docker exec -ti container_name sh

Let's say, for reasons that are your own, you really do want to use SSH. It takes a few steps, but it can be done. Here are the commands that you would run inside the container to set it up...

apt-get update
apt-get install openssh-server

mkdir /var/run/sshd
chmod 0755 /var/run/sshd
/usr/sbin/sshd

useradd --create-home --shell /bin/bash --groups sudo username ## includes 'sudo'
passwd username ## Enter a password

apt-get install x11-apps ## X11 demo applications (optional)
ifconfig | awk '/inet addr/{print substr($2,6)}' ## Display IP address (optional)

Now you can even run graphical applications (if they are installed in the container) using X11 forwarding to the SSH client:

ssh -X username@IPADDRESS
xeyes ## run an X11 demo app in the client

Here are some related resources:

• openssh-server doesn't start in Docker container
• How to get bash or ssh into a running container in background mode?
• Can you run GUI applications in a Docker container?
• Other useful approaches for graphical access found with search: Docker X11
• If you run SSHD in your Docker containers, you're doing it wrong!