Start/stop program from website

Question

I have some users on my machine that I allow to run small Mumble voice servers. I would like for them to be able to start/stop their voice server from a website (being ran by Apache). With the current set up, I have each server being run as a different user (the person's specific user account).

What I can't figure out is the best way to start/stop the server without delay. Currently, I have the website make an entry into a database whenever they want to start/stop their service. Then, I have a cron script that runs every minute look in the database for these starts/stops. That cron script will switch to the users account and run the server as that user. My issue with this is that it can take up to around 1 minute for the action to happen.

Is there a more responsive way to accomplish this?

Answer 1

Your cron method is the on the right track.. most other methods have various security concerns. To make that same idea faster, you could touch a file, and use inotify to detect that it was modified. inotify is extraordinarily fast. 'inotify-tools' is a readily available set of commandline tools that use inotify. There are some good examples on the github site for inotify-tools.

From: https://github.com/rvoicilas/inotify-tools/wiki/#wiki-info

#!/bin/sh
EVENT=$(inotifywait --format '%e' ~/file1)
[ $? != 0 ] && exit
[ "$EVENT" = "MODIFY" ] && echo 'file modified!'
[ "$EVENT" = "DELETE_SELF" ] && echo 'file deleted!'

It is basically instant - inotify is a kernel feature that these tools take advantage of which requests of the kernel notification on very specific file system events.

Answer 2

I set up something like this on one of my webservers that had a problem of sshd dying occasionally -- I wanted to manually restart sshd from an authenticated web interface. This was intended (in my case) to be a short-term solution, as a full OS upgrade was not too far off anyway.

I set up a php page similar to what nonplus suggested, using shell_exec to execute a specific command via sudo:

  $output = shell_exec("/usr/local/bin/sudo /usr/local/etc/rc.d/sshd.sh restart");
  echo "<pre>$output</pre>";

This way, I could edit the local sudoers file to give my apache user the appropriate access to specific commands. I needed to grant it the root-level privilege of starting sshd; you could limit it to starting/stopping the appropriate services as the appropriate users.

Answer 3

If these people you are hosting servers for are trustworthy and wont spam/hack the server, why not just program the web interface to directly pass the start/stop to the shell

For example, in PHP you could program this into the page:

<?php
  // checks, templating, blah, blah, blah
  $status = exec('/path/to/service/mumbled status')

  if ($status == "stopped")
    // display start button, hook exec('mumbled stop') command to it

  if ($status == "running")
    // display stop button, hook exec('mumbled start') command to it
?>

If it was me I would go that route, but that's just me.

Answer 4

Instead of, or in addition to, writing to a database, have you considered writing to a named pipe? You could create one named pipe per user and then create a process to watch each named pipe. When the 'restart' command comes, immediately restart the process.

This is not a complete solution and can be improved upon, but it should give you an idea of how you could monitor the named pipe and restart the process.

while read line <$pipe
 do
  if [[ "$line" == 'restart' ]]; then
    restart_some_service
  fi
done

Answer 5

This might be overkill, but have you considered Usermin? They list a process plugin in the standard plugins, that lets your users

View all processes running on the system, kill those belonging to [them], and start new ones.

(Never tried this, just thought it might be pretty, uhm, "professional".)

(Edit Concerning "Mumble", there seem to be some web interfaces already, but I have no idea if they help in your situation.)