How to control host from docker container?
For example, how to execute copied to host bash script?
This answer is just a more detailed version of Bradford Medeiros's solution, which for me as well turned out to be the best answer, so credit goes to him.
In his answer, he explains WHAT to do (named pipes) but not exactly HOW to do it.
I have to admit I didn't know what named pipes were when I read his solution. So I struggled to implement it (while it's actually very simple), but I did succeed.
So the point of my answer is just detailing the commands you need to run in order to get it working, but again, credit goes to him.
PART 1 - Testing the named pipe concept without docker
On the main host, chose the folder where you want to put your named pipe file, for instance /path/to/pipe/ and a pipe name, for instance mypipe, and then run:
mkfifo /path/to/pipe/mypipe
The pipe is created.
Type
ls -l /path/to/pipe/mypipe
And check the access rights start with "p", such as
prw-r--r-- 1 root root 0 mypipe
Now run:
tail -f /path/to/pipe/mypipe
The terminal is now waiting for data to be sent into this pipe
Now open another terminal window.
And then run:
echo "hello world" > /path/to/pipe/mypipe
Check the first terminal (the one with tail -f), it should display "hello world"
PART 2 - Run commands through the pipe
On the host container, instead of running tail -f which just outputs whatever is sent as input, run this command that will execute it as commands:
eval "$(cat /path/to/pipe/mypipe)"
Then, from the other terminal, try running:
echo "ls -l" > /path/to/pipe/mypipe
Go back to the first terminal and you should see the result of the ls -l command.
PART 3 - Make it listen forever
You may have noticed that in the previous part, right after ls -l output is displayed, it stops listening for commands.
Instead of eval "$(cat /path/to/pipe/mypipe)", run:
while true; do eval "$(cat /path/to/pipe/mypipe)"; done
(you can nohup that)
Now you can send unlimited number of commands one after the other, they will all be executed, not just the first one.
PART 4 - Make it work even when reboot happens
The only caveat is if the host has to reboot, the "while" loop will stop working.
To handle reboot, here what I've done:
Put the while true; do eval "$(cat /path/to/pipe/mypipe)"; done in a file called execpipe.sh with #!/bin/bash header
Don't forget to chmod +x it
Add it to crontab by running
crontab -e
And then adding
#reboot /path/to/execpipe.sh
At this point, test it: reboot your server, and when it's back up, echo some commands into the pipe and check if they are executed.
Of course, you aren't able to see the output of commands, so ls -l won't help, but touch somefile will help.
Another option is to modify the script to put the output in a file, such as:
while true; do eval "$(cat /path/to/pipe/mypipe)" &> /somepath/output.txt; done
Now you can run ls -l and the output (both stdout and stderr using &> in bash) should be in output.txt.
PART 5 - Make it work with docker
If you are using both docker compose and dockerfile like I do, here is what I've done:
Let's assume you want to mount the mypipe's parent folder as /hostpipe in your container
Add this:
VOLUME /hostpipe
in your dockerfile in order to create a mount point
Then add this:
volumes:
- /path/to/pipe:/hostpipe
in your docker compose file in order to mount /path/to/pipe as /hostpipe
Restart your docker containers.
PART 6 - Testing
Exec into your docker container:
docker exec -it <container> bash
Go into the mount folder and check you can see the pipe:
cd /hostpipe && ls -l
Now try running a command from within the container:
echo "touch this_file_was_created_on_main_host_from_a_container.txt" > /hostpipe/mypipe
And it should work!
WARNING: If you have an OSX (Mac OS) host and a Linux container, it won't work (explanation here https://stackoverflow.com/a/43474708/10018801 and issue here https://github.com/docker/for-mac/issues/483 ) because the pipe implementation is not the same, so what you write into the pipe from Linux can be read only by a Linux and what you write into the pipe from Mac OS can be read only by a Mac OS (this sentence might not be very accurate, but just be aware that a cross-platform issue exists).
For instance, when I run my docker setup in DEV from my Mac OS computer, the named pipe as explained above does not work. But in staging and production, I have Linux host and Linux containers, and it works perfectly.
PART 7 - Example from Node.JS container
Here is how I send a command from my Node.JS container to the main host and retrieve the output:
const pipePath = "/hostpipe/mypipe"
const outputPath = "/hostpipe/output.txt"
const commandToRun = "pwd && ls-l"
console.log("delete previous output")
if (fs.existsSync(outputPath)) fs.unlinkSync(outputPath)
console.log("writing to pipe...")
const wstream = fs.createWriteStream(pipePath)
wstream.write(commandToRun)
wstream.close()
console.log("waiting for output.txt...") //there are better ways to do that than setInterval
let timeout = 10000 //stop waiting after 10 seconds (something might be wrong)
const timeoutStart = Date.now()
const myLoop = setInterval(function () {
if (Date.now() - timeoutStart > timeout) {
clearInterval(myLoop);
console.log("timed out")
} else {
//if output.txt exists, read it
if (fs.existsSync(outputPath)) {
clearInterval(myLoop);
const data = fs.readFileSync(outputPath).toString()
if (fs.existsSync(outputPath)) fs.unlinkSync(outputPath) //delete the output file
console.log(data) //log the output of the command
}
}
}, 300);
Use a named pipe.
On the host OS, create a script to loop and read commands, and then you call eval on that.
Have the docker container read to that named pipe.
To be able to access the pipe, you need to mount it via a volume.
This is similar to the SSH mechanism (or a similar socket-based method), but restricts you properly to the host device, which is probably better. Plus you don't have to be passing around authentication information.
My only warning is to be cautious about why you are doing this. It's totally something to do if you want to create a method to self-upgrade with user input or whatever, but you probably don't want to call a command to get some config data, as the proper way would be to pass that in as args/volume into docker. Also, be cautious about the fact that you are evaling, so just give the permission model a thought.
Some of the other answers such as running a script. Under a volume won't work generically since they won't have access to the full system resources, but it might be more appropriate depending on your usage.
The solution I use is to connect to the host over SSH and execute the command like this:
ssh -l ${USERNAME} ${HOSTNAME} "${SCRIPT}"
UPDATE
As this answer keeps getting up votes, I would like to remind (and highly recommend), that the account which is being used to invoke the script should be an account with no permissions at all, but only executing that script as sudo (that can be done from sudoers file).
UPDATE: Named Pipes
The solution I suggested above was only the one I used while I was relatively new to Docker. Now in 2021 take a look on the answers that talk about Named Pipes. This seems to be a better solution.
However, nobody there mentioned anything about security. The script that will evaluate the commands sent through the pipe (the script that calls eval) must actually not use eval for the whole pipe output, but to handle specific cases and call the required commands according to the text sent, otherwise any command that can do anything can be sent through the pipe.
That REALLY depends on what you need that bash script to do!
For example, if the bash script just echoes some output, you could just do
docker run --rm -v $(pwd)/mybashscript.sh:/mybashscript.sh ubuntu bash /mybashscript.sh
Another possibility is that you want the bash script to install some software- say the script to install docker-compose. you could do something like
docker run --rm -v /usr/bin:/usr/bin --privileged -v $(pwd)/mybashscript.sh:/mybashscript.sh ubuntu bash /mybashscript.sh
But at this point you're really getting into having to know intimately what the script is doing to allow the specific permissions it needs on your host from inside the container.
My laziness led me to find the easiest solution that wasn't published as an answer here.
It is based on the great article by luc juggery.
All you need to do in order to gain a full shell to your linux host from within your docker container is:
docker run --privileged --pid=host -it alpine:3.8 \
nsenter -t 1 -m -u -n -i sh
Explanation:
--privileged : grants additional permissions to the container, it allows the container to gain access to the devices of the host (/dev)
--pid=host : allows the containers to use the processes tree of the Docker host (the VM in which the Docker daemon is running)
nsenter utility: allows to run a process in existing namespaces (the building blocks that provide isolation to containers)
nsenter (-t 1 -m -u -n -i sh) allows to run the process sh in the same isolation context as the process with PID 1.
The whole command will then provide an interactive sh shell in the VM
This setup has major security implications and should be used with cautions (if any).
Write a simple server python server listening on a port (say 8080), bind the port -p 8080:8080 with the container, make a HTTP request to localhost:8080 to ask the python server running shell scripts with popen, run a curl or writing code to make a HTTP request curl -d '{"foo":"bar"}' localhost:8080
#!/usr/bin/python
from BaseHTTPServer import BaseHTTPRequestHandler,HTTPServer
import subprocess
import json
PORT_NUMBER = 8080
# This class will handles any incoming request from
# the browser
class myHandler(BaseHTTPRequestHandler):
def do_POST(self):
content_len = int(self.headers.getheader('content-length'))
post_body = self.rfile.read(content_len)
self.send_response(200)
self.end_headers()
data = json.loads(post_body)
# Use the post data
cmd = "your shell cmd"
p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
p_status = p.wait()
(output, err) = p.communicate()
print "Command output : ", output
print "Command exit status/return code : ", p_status
self.wfile.write(cmd + "\n")
return
try:
# Create a web server and define the handler to manage the
# incoming request
server = HTTPServer(('', PORT_NUMBER), myHandler)
print 'Started httpserver on port ' , PORT_NUMBER
# Wait forever for incoming http requests
server.serve_forever()
except KeyboardInterrupt:
print '^C received, shutting down the web server'
server.socket.close()
If you are not worried about security and you're simply looking to start a docker container on the host from within another docker container like the OP, you can share the docker server running on the host with the docker container by sharing it's listen socket.
Please see https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface and see if your personal risk tolerance allows this for this particular application.
You can do this by adding the following volume args to your start command
docker run -v /var/run/docker.sock:/var/run/docker.sock ...
or by sharing /var/run/docker.sock within your docker compose file like this:
version: '3'
services:
ci:
command: ...
image: ...
volumes:
- /var/run/docker.sock:/var/run/docker.sock
When you run the docker start command within your docker container,
the docker server running on your host will see the request and provision the sibling container.
credit: http://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/
As Marcus reminds, docker is basically process isolation. Starting with docker 1.8, you can copy files both ways between the host and the container, see the doc of docker cp
https://docs.docker.com/reference/commandline/cp/
Once a file is copied, you can run it locally
docker run --detach-keys="ctrl-p" -it -v /:/mnt/rootdir --name testing busybox
# chroot /mnt/rootdir
#
I have a simple approach.
Step 1: Mount /var/run/docker.sock:/var/run/docker.sock (So you will be able to execute docker commands inside your container)
Step 2: Execute this below inside your container. The key part here is (--network host as this will execute from host context)
docker run -i --rm --network host -v /opt/test.sh:/test.sh alpine:3.7
sh /test.sh
test.sh should contain the some commands (ifconfig, netstat etc...) whatever you need.
Now you will be able to get host context output.
You can use the pipe concept, but use a file on the host and fswatch to accomplish the goal to execute a script on the host machine from a docker container. Like so (Use at your own risk):
#! /bin/bash
touch .command_pipe
chmod +x .command_pipe
# Use fswatch to execute a command on the host machine and log result
fswatch -o --event Updated .command_pipe | \
xargs -n1 -I "{}" .command_pipe >> .command_pipe_log &
docker run -it --rm \
--name alpine \
-w /home/test \
-v $PWD/.command_pipe:/dev/command_pipe \
alpine:3.7 sh
rm -rf .command_pipe
kill %1
In this example, inside the container send commands to /dev/command_pipe, like so:
/home/test # echo 'docker network create test2.network.com' > /dev/command_pipe
On the host, you can check if the network was created:
$ docker network ls | grep test2
8e029ec83afe test2.network.com bridge local
In my scenario I just ssh login the host (via host ip) within a container and then I can do anything I want to the host machine
I found answers using named pipes awesome. But I was wondering if there is a way to get the output of the executed command.
The solution is to create two named pipes:
mkfifo /path/to/pipe/exec_in
mkfifo /path/to/pipe/exec_out
Then, the solution using a loop, as suggested by #Vincent, would become:
# on the host
while true; do eval "$(cat exec_in)" > exec_out; done
And then on the docker container, we can execute the command and get the output using:
# on the container
echo "ls -l" > /path/to/pipe/exec_in
cat /path/to/pipe/exec_out
If anyone interested, my need was to use a failover IP on the host from the container, I created this simple ruby method:
def fifo_exec(cmd)
exec_in = '/path/to/pipe/exec_in'
exec_out = '/path/to/pipe/exec_out'
%x[ echo #{cmd} > #{exec_in} ]
%x[ cat #{exec_out} ]
end
# example
fifo_exec "curl https://ip4.seeip.org"
Depending on the situation, this could be a helpful resource.
This uses a job queue (Celery) that can be run on the host, commands/data could be passed to this through Redis (or rabbitmq). In the example below, this is occurring in a django application (which is commonly dockerized).
https://www.codingforentrepreneurs.com/blog/celery-redis-django/
To expand on user2915097's response:
The idea of isolation is to be able to restrict what an application/process/container (whatever your angle at this is) can do to the host system very clearly. Hence, being able to copy and execute a file would really break the whole concept.
Yes. But it's sometimes necessary.
No. That's not the case, or Docker is not the right thing to use. What you should do is declare a clear interface for what you want to do (e.g. updating a host config), and write a minimal client/server to do exactly that and nothing more. Generally, however, this doesn't seem to be very desirable. In many cases, you should simply rethink your approach and eradicate that need. Docker came into an existence when basically everything was a service that was reachable using some protocol. I can't think of any proper usecase of a Docker container getting the rights to execute arbitrary stuff on the host.
I am writing a test suite for a web application using Selenium.
In the course of which I need to test behaviour of the app in case a certain service is running or not.
I wanted to create a cgi call to a Python script turning that service on and off.
I know that the cgi call is in the context of the webserver (Apache) however thought that issuing sudo calls like so:
import subprocess
import os
command = 'sudo -S launchctl unload /Library/LaunchAgents/com.my.daemon.plist'
pwd = 'pwd123'
test1 = subprocess.Popen( command, shell=True, stdin=subprocess.PIPE)
test1.communicate(input=pwd)
test2 = os.system( 'echo %s|%s' % (pwd,command) )
would do the trick, well they don't I get return code 256.
What can I do to have this call be executed w/o touching the context in which Apache runs?
As for security: this will only run on a test machine.
The user that Apache runs as needs to be in the /etc/sudoers file, or belong to the sudo group, which I guess it usually doesn't. You also need to make it not ask for a password, which is configured in /etc/sudoers
For Ubuntu, check these out: https://askubuntu.com/questions/7477/how-can-i-add-a-new-user-as-sudoer-using-the-command-line
https://askubuntu.com/questions/147241/execute-sudo-without-password
It could potentially be a pathing issue..
Have you tried writing out the full path like this:
command = '/usr/bin/sudo -S launchctl unload /Library/LaunchAgents/com.my.daemon.plist'
command should be a list, not a string. Try with:
command = ['sudo', '-S', 'launchctl', 'unload', '/Library/LaunchAgents/com.my.daemon.plist']
Cant run sudo this way -- sudo needs a controlling terminal to run.
I have a very strange issue that I can't seem to figure out.
When I execute a python script containing the following lines while inside a SSH terminal (putty), it works fine. But the moment I run the script via crontab or even nohup python myscript >/dev/null 2>&1& it doesn't seem to execute these commands.
subprocess.call('rsync -avr /path/to/folder/. --include "delta.*" --exclude "*" -e "ssh -o StrictHostKeyChecking=no -i /path/to/key.pem" ec2-user#'+server+':/path/to/folder/', shell=True)
local('ssh -t -o StrictHostKeyChecking=no -i /path/to/key.pem ec2-user#'+server+' "sudo /usr/bin/indexer -c /path/to/sphinx.conf --merge main delta --rotate"')
Basically all the above is doing is syncing a folder with new sphinx search engine updates to a remote server, then the second line runs a remote ssh command to force the search engine to rotate updates into production.
I do have fabric installed (hence the local command) but to avoid having to fab a second file I was hoping a single line of code could allow me to execute sudo commands on a remote server.
Can someone help me out?
I found the answer, for ssh commands in a script run in the background, you need to to have -t -t to force a pseudo terminal.
Reference:
Pseudo-terminal will not be allocated because stdin is not a terminal
i have googled a lot,and in fabric faq also said use screen dtach with it ,but didn't find how to implement it?
bellow is my wrong code,the sh will not execute as excepted it is a nohup task
def dispatch():
run("cd /export/workspace/build/ && if [ -f spider-fetcher.zip ];then mv spider-fetcher.zip spider-fetcher.zip.bak;fi")
put("/root/build/spider-fetcher.zip","/export/workspace/build/")
run("cd /export/script/ && sh ./restartCrawl.sh && echo 'finished'")
I've managed to do it in two steps:
Start tmux session on remote server in detached mode:
run("tmux new -d -s foo")
Send command to the detached tmux session:
run("tmux send -t foo.0 ls ENTER")
here '-t' determines target session ('foo') and 'foo.0' tells the
number of the pane the 'ls' command is to be executed in.
you can just prepend screen to the command you want to run:
run("screen long running command")
Fabric though doesn't keep state like something like expect would, as each run/sudo/etc are their own sperate command runs without knowing the state of the last command. Eg run("cd /var");run("pwd") will not print /var but the home dir of the user who has logged into the box.
Through Fabric, I am trying to start a celerycam process using the below nohup command. Unfortunately, nothing is happening. Manually using the same command, I could start the process but not through Fabric. Any advice on how can I solve this?
def start_celerycam():
'''Start celerycam daemon'''
with cd(env.project_dir):
virtualenv('nohup bash -c "python manage.py celerycam --logfile=%scelerycam.log --pidfile=%scelerycam.pid &> %scelerycam.nohup &> %scelerycam.err" &' % (env.celery_log_dir,env.celery_log_dir,env.celery_log_dir,env.celery_log_dir))
I'm using Erich Heine's suggestion to use 'dtach' and it's working pretty well for me:
def runbg(cmd, sockname="dtach"):
return run('dtach -n `mktemp -u /tmp/%s.XXXX` %s' % (sockname, cmd))
This was found here.
As I have experimented, the solution is a combination of two factors:
run process as a daemon: nohup ./command &> /dev/null &
use pty=False for fabric run
So, your function should look like this:
def background_run(command):
command = 'nohup %s &> /dev/null &' % command
run(command, pty=False)
And you can launch it with:
execute(background_run, your_command)
This is an instance of this issue. Background processes will be killed when the command ends. Unfortunately on CentOS 6 doesn't support pty-less sudo commands.
The final entry in the issue mentions using sudo('set -m; service servicename start'). This turns on Job Control and therefore background processes are put in their own process group. As a result they are not terminated when the command ends.
For even more information see this link.
you just need to run
run("(nohup yourcommand >& /dev/null < /dev/null &) && sleep 1")
DTACH is the way to go. It's a software you need to install like a lite version of screen.
This is a better version of the "dtach"-method found above, it will install dtach if necessary. It's to be found here where you can also learn how to get the output of the process which is running in the background:
from fabric.api import run
from fabric.api import sudo
from fabric.contrib.files import exists
def run_bg(cmd, before=None, sockname="dtach", use_sudo=False):
"""Run a command in the background using dtach
:param cmd: The command to run
:param output_file: The file to send all of the output to.
:param before: The command to run before the dtach. E.g. exporting
environment variable
:param sockname: The socket name to use for the temp file
:param use_sudo: Whether or not to use sudo
"""
if not exists("/usr/bin/dtach"):
sudo("apt-get install dtach")
if before:
cmd = "{}; dtach -n `mktemp -u /tmp/{}.XXXX` {}".format(
before, sockname, cmd)
else:
cmd = "dtach -n `mktemp -u /tmp/{}.XXXX` {}".format(sockname, cmd)
if use_sudo:
return sudo(cmd)
else:
return run(cmd)
May this help you, like it helped me to run omxplayer via fabric on a remote rasberry pi!
You can use :
run('nohup /home/ubuntu/spider/bin/python3 /home/ubuntu/spider/Desktop/baidu_index/baidu_index.py > /home/ubuntu/spider/Desktop/baidu_index/baidu_index.py.log 2>&1 &', pty=False)
nohup did not work for me and I did not have tmux or dtach installed on all the boxes I wanted to use this on so I ended up using screen like so:
run("screen -d -m bash -c '{}'".format(command), pty=False)
This tells screen to start a bash shell in a detached terminal that runs your command
You could be running into this issue
Try adding 'pty=False' to the sudo command (I assume virtualenv is calling sudo or run somewhere?)
This worked for me:
sudo('python %s/manage.py celerycam --detach --pidfile=celerycam.pid' % siteDir)
Edit: I had to make sure the pid file was removed first so this was the full code:
# Create new celerycam
sudo('rm celerycam.pid', warn_only=True)
sudo('python %s/manage.py celerycam --detach --pidfile=celerycam.pid' % siteDir)
I was able to circumvent this issue by running nohup ... & over ssh in a separate local shell script. In fabfile.py:
#task
def startup():
local('./do-stuff-in-background.sh {0}'.format(env.host))
and in do-stuff-in-background.sh:
#!/bin/sh
set -e
set -o nounset
HOST=$1
ssh $HOST -T << HERE
nohup df -h 1>>~/df.log 2>>~/df.err &
HERE
Of course, you could also pass in the command and standard output / error log files as arguments to make this script more generally useful.
(In my case, I didn't have admin rights to install dtach, and neither screen -d -m nor pty=False / sleep 1 worked properly for me. YMMV, especially as I have no idea why this works...)