Control-C issues duplicate signals to container

[ryanuber]

• I have tried with the latest version of Docker Desktop
• I have tried disabling enabled experimental features
• I have uploaded Diagnostics
• Diagnostics ID: BD253A61-8FD5-49F8-BC42-41EFE6A5AC2A/20210112212415

Expected behavior

Running a container in the foreground via docker run and pressing ctrl-c sends exactly one signal (defined by STOPSIGNAL in the Dockerfile) to the running process.

Actual behavior

Two signals are sent to the running container, causing undesired behavior in the running application. Running with -it (interactive, TTY) produces a single signal, as expected.

Information

• Is it reproducible? Yes
• Is the problem new? Yes - this seems to have been a behavior change at Docker Desktop 2.4.0. Prior versions send a single signal as expected.
• Did the problem appear with an update? Versions from 2.4.0 onward exhibit the unexpected multiple signals behavior.
• macOS Version: 10.15.7

Steps to reproduce the behavior

1. Create a Dockerfile with the following content:

FROM ubuntu:20.04

COPY sig.sh /sig.sh
RUN chmod +x /sig.sh

STOPSIGNAL SIGINT

ENTRYPOINT ["/sig.sh"]

2. Create a script file sig.sh with the following content:

#!/bin/bash

trap "register" INT

register() {
    echo "INT"
    [ -z "$SIG" ] && SIG=1 || exit
}

while true; do
    sleep 100 &
    wait
done

3. Build the container with docker build -t signal-test:latest .
4. Run the container with docker run signal-test:latest
5. Press ctrl+c once. Note that INT is printed twice, thus indicating that two signals were sent to the process.

[stephen-turner]

Interesting. I can reproduce this on Windows too.

[StefanScherer]

Indeed, there is a different behaviour between a Linux-only environment and Docker Desktop.

I've built your test image and ran it on Ubuntu 20.04 with Docker Engine 20.10.2, and I have to press CTRL+C twice to exit the container:

Docker Desktop for Mac 3.1.0 with Docker Engine 20.10.2 sends the signal twice with just one CTRL+C:

[thaJeztah]

does it still reproduce if you disable "cloud experience" under experimental features in the Docker Desktop preferences?

[StefanScherer]

@thaJeztah Good catch!

Without the cloud experience (or running com.docker.cli directly) it behaves just like directly on a Linux system:

[ryanuber]

Interesting! I had only disabled the CLI experimental features, but I confirmed disabling Cloud Experience does indeed fix the problem. com.docker.cli executed directly while Cloud Experience is enabled also works as expected. Nice catch!

[thaJeztah]

@rumpl @gtardif ^ ptal looks to be an issue in https://github.com/docker/compose-cli

[stephen-turner]

I'm just going to move the ticket to that repo.

[ndeloof]

Internaly tracked as https://docker.atlassian.net/browse/IL-268