CODEWITHSUNDEEP
linuxsignalsdocker
atupal
atupal

Reputation: 17210

How to send signal to program run in a docker container?

I have a program run in a docker container with detached mode.

So how to send a signal such as SIGINT to this program?

Upvotes: 54

Views: 46444

Answers (5)

Marek
Marek

Reputation: 1788

When working with compose this was useful for me:

docker compose kill -s <SIGNAL> <compose service name>

This will send specified signal to container's root process.

For example, I had a problem with reloading gunicorn WSGI server process inside the container. docker compose kill -s HUP <my service name> solved the issue.

Upvotes: 1

Andy
Andy

Reputation: 38237

You can use docker kill --signal="<signal>" <container name or id> to send any signal to the root process of a given container.

See https://docs.docker.com/engine/reference/commandline/kill/#send-a-custom-signal--to-a-container

Upvotes: 110

hipokito
hipokito

Reputation: 463

I managed to send a signal I want to a process(program) in docker container by:

  1. Getting the ID of the container - docker ps | grep yourProgramName - for me it looks like so - 4b6425cf4261
  2. Login into the container using docker exec -it 4b6425cf4261 bash
  3. List all the running processes with ps -A
  4. Find the PID of the process you want to send a SIGINT to
  5. Send the signal to it: kill -SIGINT PID (example: kill -SIGINT 15)

Upvotes: 5

Sudhanshu Dev
Sudhanshu Dev

Reputation: 388

  • docker kill used to send signal to main container process i.e process with PID 1.
  • Any application with PID 1 can handle signals directly. Below command kill the main docker process: $ docker kill --signal="SIGTERM" container-id/name
  • But application which does not have PID 1 i.e application is background process:
    • We can not send single directly to any background process running within docker container.
    • In this case we need to trap and handle the user defined signal in the shell script running as entry point.
  • Let's we have the following Dockerfile. (Update it as per the application)
FROM centos:6.7
# Install/Deploye the service below.

# Copy the shell script.
COPY entrypoint.sh /home
EXPOSE 8080
ENTRYPOINT ["/home/entrypoint.sh"]

  • Below is the entrypoint.sh. (Update it it as per the application). Suppose we wants to restart a init.d service.

    #start the service
/etc/init.d/<servicename> start
pid="$!"

# SIGUSR1- Single handler
my_handler() {
    /etc/init.d/<servicename> restart
}

# Trap and handle the user defind singnal.
trap 'my_handler' SIGUSR1

# wait forever(Alive container.)
while true
do
    tail -f /dev/null & wait ${!}
done
  • Build the docker image and run the container.
  • Now you can restart the service from Host machine: $docker kill --signal="SIGUSR1" container-id/name

Upvotes: 10

Regan
Regan

Reputation: 8791

You can use nsenter to get into your container space and send your signal.

PID=$(docker inspect --format {{.State.Pid}} <container_name_or_ID>)
nsenter --target $PID --mount --uts --ipc --net --pid kill -SIGINT <PID of your program inside your container>

More info : http://jpetazzo.github.io/2014/06/23/docker-ssh-considered-evil/

Upvotes: 14

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