Say I run this Docker command in one Terminal window:
$ docker run --name stackoverflow --rm ubuntu /bin/bash -c "sleep 5"
And before it exits I run this in a second Terminal window:
$ docker run -it --rm --pid=container:stackoverflow terencewestphal/htop
I'll successfully see htop running in the second container, displaying the bash sleep process running. So far so good.
After 5 seconds, the first container will exit with code 0. All good.
At this time, the second container will exit with code 137 (SIGILL). This also makes sense to me since the second container is just attached to the first one.
The problem is that this messes up macOS's Terminal.app's state:
The Terminal's cursor disappears.
Clicking the Terminal window causes mouse location characters to be entered as input.
I'm hoping to find a way to avoid messing up Terminal.app state. Any suggestions?
You can't avoid such behaviour, because it is the htop duty to setup the terminal state after its termination, but it can't do it when terminated with SIGKILL. However, you can fix this terminal window yourself with the reset command, which is intended to initialize the terminal state.
About the "attached" container:
The --pid=container:<name> option means that the new container would be run in the PID namespace of first container and as the pid_namespaces(7) man page says:
If the "init" process of a PID namespace terminates, the kernel
terminates all of the processes in the namespace via a SIGKILL signal.
Related
I want a custom bash script in the container that is called automatically before the container stops (docker stop or ctrl + c).
According to this docker doc and multiple StackOverflow threads, I need to catch the SIGTERM signal in the container and then run my custom script when the event appears. As I know SIGTERM can be only used from a root process with PID 1.
Relevand part of my Dockerfile:
...
COPY container-scripts/entrypoint.sh /
ENTRYPOINT ["/entrypoint.sh"]
I use [] to define the entrypoint and as I know this will run my script directly, without having a /bin/sh -c wrapper (PID 1), and when the script eventually exec another process, that process becomes the main process and will receive the docker stop signal.
entrypoint.sh:
...
# run the external bash script if it exists
BOOT_SCRIPT="/boot.sh"
if [ -f "$BOOT_SCRIPT" ]; then
printf ">> executing the '%s' script\n" "$BOOT_SCRIPT"
source "$BOOT_SCRIPT"
fi
# start something here
...
The boot.sh is used by child containers to execute something else that the child container wants. Everything is fine, my containers work like a charm.
ps axu in a child container:
PID USER TIME COMMAND
1 root 0:00 {entrypoint.sh} /bin/bash /entrypoint.sh
134 root 0:25 /usr/lib/jvm/java-17-openjdk/bin/java -server -D...
...
421 root 0:00 ps axu
Before stopping the container I need to run some commands automatically so I created a shutdown.sh bash script. This script works fine and does what I need. But I execute the shutdown script manually this way:
$ docker exec -it my-container /bin/bash
# /shutdown.sh
# exit
$ docker container stop my-container
I would like to automate the execution of the shutdown.sh script.
I tried to add the following to the entrypoint.sh but it does not work:
trap "echo 'hello SIGTERM'; source /shutdown.sh; exit" SIGTERM
What is wrong with my code?
Your help and comments guided me in the right direction.
I went through again the official documentations here, here, and here and finally I found what was the problem.
The issue was the following:
My entrypoint.sh script, which kept alive the container executed the following command at the end:
# start the ssh server
ssh-keygen -A
/usr/sbin/sshd -D -e "$#"
The -D option runs the ssh daemon in a NOT detach mode and sshd does not become a daemon. Actually, that was my intention, this is the way how I kept alive the container.
But this foreground process prevented to be executed properly the trap command. I changed the way how I started the sshd app and now it runs as a normal background process.
Then, I added the following command to keep alive my docker container (this is a recommended best practice):
tail -f /dev/null
But of course, the same issue appeared. Tail runs as a foreground process and the trap command does not do its job.
The only way how I can keep alive the container and let the entrypoint.sh runs as a foreign process in docker is the following:
while true; do
sleep 1
done
This way the trap command works fine and my bash function that handles the SIGINT, etc. signals runs properly when the time comes.
But honestly, I do not like this solution. This endless loop with a sleep looks ugly, but I have no idea at the moment how to manage it in a nice way :(
But this is another question that not belongs to this thread (but could be great if you can suggest my a better solution).
In https://squidfunk.github.io/mkdocs-material/creating-your-site/#previewing-as-you-write, there's a command that will launch my document site.
docker run --rm -it -p 8000:8000 -v ${PWD}:/docs squidfunk/mkdocs-material
I want that after it is launch, I will automatically open the browser and see it.
I write a script as below
docker run --rm -it -p 8000:8000 -v ${PWD}:/docs squidfunk/mkdocs-material
open http://localhost:8000
But it turns out the open command cannot be triggered, as the previous docker run is still holding the process still.
If I use & as below, then the open will get called too fast before the page is ready
docker run --rm -it -p 8000:8000 -v ${PWD}:/docs squidfunk/mkdocs-material &
open http://localhost:8000
How can I get open called at the right time?
(FYI, I'm using GNU bash, version 3.2.57(1)-release)
How can I get open called at the right time?
Opening the browser at exactly the right time would require your server mkdocs to give some signal that it is ready. Since you probably don't want to modify the code of the server, you just have to wait for the right time and then open the page.
Either measure the startup time once by hand and then use a fixed wait time or check the page repeatedly until it loads.
In both cases, the docker command and the process of opening the page must run in parallel. bash can run run things in parallel using background jobs (... &). Since docker -it must run in the foreground, we run open as a the background job. This might seem a little strange, since we seemingly open the website before starting the server, but keep in mind that both commands run in parallel.
Either
# replace 2 with your measured time
sleep 2 && open http://localhost:8000 &
docker run --rm -it -p 8000:8000 -v "${PWD}:/docs" squidfunk/mkdocs-material
or
while ! curl http://localhost:8000 -s -f -o /dev/null; do
sleep 0.2
done && open http://localhost:8000 &
docker run --rm -it -p 8000:8000 -v "${PWD}:/docs" squidfunk/mkdocs-material
It sounds (to me) like:
docker run is a blocking process (it does not exit and/or return control to the console) so ...
the open is never run (unless the docker run command is aborted in which case the open will fail), and ...
pushing docker run into the background means the open is run before the URL is fully functional
If this is the case I'm wondering if you could do something like:
docker run ... & # put in background, return control to console
sleep 3 # sleep 3 seconds
open ...
NOTE: manually picking the number of seconds to sleep (3 in this case) isn't ideal but a decent number that guarantees URL availability and doesn't leave you hanging should be doable with some testing
Another 'basic' option might be a looping construct combined with a sleep, eg:
docker run ... &
while true # loop indefinitely
do
sleep 1 # sleep 1 sec
open ... 2>/dev/null # try the open
[[ $? == 0 ]] && break # if it doesn't fail then break out of loop, ie,
# if it does fail then repeat loop
done
In my Travis CI, part of my verification is to start a docker container and verify that it doesn't fail within 10 seconds.
I have a yarn script docker:run:local that calls docker run -it <mytag> node app.js.
If I call the yarn script with timeout from a bash shell, it works fine:
$ timeout 10 yarn docker:run:local; test $? -eq 124 && echo "Container ran for 10 seconds without error"
This calls docker run, lets it run for 10 seconds, then kills it (if not already returned). If the exit code is 124, the timeout did expire, which means the container was still running. Exactly what I need to verify that my docker container is reasonably sane.
However, as soon as I run this same command from within a script, either in a test.sh file called from the shell, or if putting it in another yarn script and calling yarn test:docker, the behaviour is completely different. I get:
ERRO[0000] error waiting for container: context canceled
Then the command hangs forever, there's no 10 second timeout, I have to ctrl-Z it and then kill -9 the process. If I run top I now have a docker process using all my CPU forever. If using timeout with any other command like sleep 20 && echo "Finished sleeping", this does not happen, so I suspect it may have something to do with how docker works in interactive mode or something, but that's only my guess.
What's causing timeout docker:run to fail from a script but work fine from a shell and how do I make this work?
Looks like running docker in interactive mode is causing the issue.
Run docker in detached more by removing the -it and allowing it to run in default detached mode or specify -d instead of -it and so:
docker run -d <mytag> node
or
docker run <mytag> node
The requirement is inside a big while loop, given a specific docker container ID, I need to monitor the docker stop event using docker event command. When I found the event, I need to quit the docker event read.
The simplified bash script I wrote is as follows:
#! /bin/bash
while true
do
## other logics
docker events --filter='container=...' --filter='event=stop' | while read event
do
echo $event
break
done
echo "got here"
## other logics
done
So in one bash session, I would run this script, in another bash session, I would type the following command:
docker container stop cassandra-1
The problem is when I execute this bash program, I can capture the stop event, and print the event, but this command will read event repeated. How to quit the docker events and print "got here" ?
I've spent lots of time searching solution online, but can't find any good approach. I once considered using break, but it doesn't work, and I also considered kill -9 $$, but I will quit the entire script program. But I only need to quit the docker event instead of big while loop.
any good advice? Thanks so much!
I found the solution. Key point is to know how docker event command actually work. Based on my research, docker event will generate a process and stuck in the foreground process. You should CTRL+C to quit (refer to: https://docs.docker.com/engine/reference/commandline/events). So you can not use break to get out of it. The approach is to execute docker event command in the background job and kill it when I found the event.
the code is as follows:
(docker events --filter 'container='"$container_id"'' --filter 'event=stop' &) | while read event
do
# kill this backgroud process
pkill -f "docker event.*stop"
done
Is there any native way to make a Docker container stop itself? I can't find anything in the documentation.
I have a container that does some stuff, and I want to hook into the completion of that.
One way I thought of doing this was blocking with docker wait until the container stops itself, and then I can restart it with a docker start and continue on to the subsequent commands that depend on those jobs being complete.
For instance:
docker run -d --name=my-container ...
# Wait for my-container to stop itself
docker wait my-container
# Once it stops itself, start it again.
docker start my-container
# Some other commands here that depend on my-container to finish its jobs...
But I can't find any way on the documentation to make a container stop itself.
There is docker stop to stop a container from outside. To stop a container from inside, you could kill the entrypoint process (the process specified in your docker run command, or the ENTRYPOINT or last CMD specified in the Dockerfile, etc.).
Don't run the container in detached mode (remove the -d) It'll run in the foreground until the entrypoint/cmd exits.
You may need to use the pseudo-tty (-t) command-line option.