I can't get env var in the Docker container

Question

I've ran my Docker container using this command: docker run --name test1 -d -e FLAG='***' rastasheep/ubuntu-sshd Now, when I connect to it via SSH, I can't get my env there via printenv FLAG. How can I fix this? When running with -it and sh, I can my get env via printenv FLAG.

Answer 1

Now, when I connect to it via SSH, I can't get my env there via printenv FLAG. How can I fix this? When running with -it and sh, I can my get env via printenv FLAG

You are doing two different things:

• docker run -it -e FLAG='***' rastasheep/ubuntu-sshd sh will run a container in interactive mode with a shell, and this shell session will have the environment variable you passed on the command line. With docker run -d -e FLAG='***' rastasheep/ubuntu-sshd, a SSH daemon process will start with defined env vars.
• when you connect in the container with SSH you will create a new shell session which does not have these environment variable set.

This can be observed when running a container, connecting to it using ssh and showing all processes and their environment variable:

docker run -d -p 2222:22 -e FLAG='test' rastasheep/ubuntu-sshd
ssh root@localhost -p 2222
...

We are now connected into the container, we can see the SSH daemon process (PID 1) and our SSH session process (PID 7):

root@788fa982c2d0:~# ps -xf
  PID TTY      STAT   TIME COMMAND
    1 ?        Ss     0:00 /usr/sbin/sshd -D  # <== does have the FLAG env var
    7 ?        Ss     0:00 sshd: root@pts/0   # <== no FLAG env var

Lets check it out, print our current process env var, and the env var of the SSH daemon process:

root@788fa982c2d0:~# printenv FLAG # Nothing
root@788fa982c2d0:~# cat /proc/1/environ # We see the FLAG env var!
[..]FLAG=test[...]

As pointed out by @Dmitrii, you can read Dockerize an SSH service for more details.

Answer 2

Try Using below Command:

docker exec <container-id> bash -c 'echo "$<variable-name>"'