Why is executing "docker exec" killing my SSH session?

Question

Let's say I have two servers, A and B. I also have a bash script that is executed on server A that looks like this:

build_test.sh

#!/bin/bash
ssh user@B <<'ENDSSH'
echo "doing test"
bash -ex test.sh
echo "completed test"
ENDSSH

test.sh

#!/bin/bash
docker exec -i my_container /bin/bash -c "echo hi!"

The problem is that completed test does not get printed to the terminal.

Here's the output of running build_test.sh:

$ ./build_test
doing test
+ docker exec -i my_container /bin/bash -c "echo hi!"
hi!

I'm expecting completed test to be output after hi!, but it isn't. How do I fix this?

`docker` is probably consuming the rest of the standard input it inherits from `ssh` (which is the script you are trying to run). — chepner, Apr 19 '19 at 17:39
I still want the output of `docker exec` to be printed to stdout. Won't removing `-i` prevent the output of `docker exec` from being printed to stdout? — Nathan Jones, Apr 19 '19 at 22:51
@NathanJones the `-i` is for stdin. You'll get stdout/stderr as long as you do not detach with `-d`. — BMitch, Apr 21 '19 at 02:02

score 2 · Accepted Answer · answered Apr 19 '19 at 18:36

docker is consuming, though not using, its standard input, which it inherits from test.sh. test.sh inherits its standard input from bash, which inherits its standard input from ssh. This means that docker itself is reading the last line of the script before the remote shell can.

To fix, just redirect docker's standard input from /dev/null.

docker exec -i my_container /bin/bash -c "echo hi!" < /dev/null

Why is executing "docker exec" killing my SSH session?

build_test.sh

test.sh

1 Answers1