I ran an Alpine Docker container using the following command:
docker run -itd --env "my_env_var=test" --name mycontainer alpine
Now when I run the env
command from inside the Docker container to get all the Env vars, I get the following output:
$ docker exec -it mycontainer /bin/sh
$ env
HOSTNAME=9de9045b5264
SHLVL=1
HOME=/root
my_env_var=test
TERM=xterm
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/
So far, so good.
But when I try to get the Environment Variables using the docker inspect
command, I see that too many ENV vars are missing (Only 2 of them are found):
$ docker inspect mycontainer
...
...
"Env": [
"my_env_var=test",
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
...
...
Also, I used the docker exec
command to print the ENV vars using the following command:
$ docker exec mycontainer /bin/sh -c env
HOSTNAME=9de9045b5264
SHLVL=1
HOME=/root
my_env_var=test
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/
This time, all the ENV vars were displayed except for the TERM=xterm
.
I observed this behaviour with centos Docker images as well. Why is it so that all the ENV vars are not getting printed using docker inspect
or docker exec
?
2
Answers
Because
/bin/sh
sets them.This happens because those environment variables are set by the binaries you are using to display them — here
/bin/sh
.There are mechanisms in Linux distributions allowing you setting variables for an interactive shell, like /etc/profile to cite only one out of them.
A better command to run in order to have something closer to what your
inspect
command would give you would be:Which gives
For the different commands that are giving you the
TERM
variable, this is caused by the-t
option of docker:We can show this using
Which gives
Versus
Which gives
Little side note on the usage of
docker inspect
: you can also filter the output with theformat
flag to get only the information you need:e.g.:
Gives