HTTP Server stops after some time

Question

INFO: I'm referring to this question I asked on Super User, but couldn't get an answer. Since my system is a RaspberryPi running Debian I think this is a good place for it.

I'm currently running a simple Node.JS server with express.js on my RaspberryPi with Debian installed on it. Everything works fine, but every morning I wake up to see my server isn't running anymore (the server process I started with the command node main.js).

My first guess was, that the Pi has some kind of sleep mode, which it enters after a couple of hours without traffic/etc, and which shuts down the server, but I also run a dydns-client, which is still up every morning (I also was informed, that the RaspberryPi doesn't come with a sleep mode).

I wrote a simple script to check whether the process is running and writes it into a log file, but today morning I had to notice, that this script was wasn't running as well (only for around two hours, it logs the server state every 15 seconds and the last state was running).

Here is the script:

#!/bin/sh                                                                                                                                     

MATCH="SOME_PROCESS_NAME"                                                                                                

while [ true ]                                                                                                                                
 do                                                                                                                                            
   if [ "$(ps -ef | grep ${MATCH} | grep -v grep)" ]; then                                                                                     
     echo "$(date): Process is running ..."                                                                                                    
   else                                                                                                                                        
     echo "$(date): Process has ended ..."                                                                                                                                                                                                                    
   fi                                                                                                                                          

   sleep 15                                                                                                                                     
done 

Is there a way to track a process after I started it to check tomorrow morning, what killed my process or why it ended (the script obviously didn't work)?

The server itself looks pretty simple and I don't think there is some kind of auto-shutdown I missed. Here is the code I used.

var express = require('express');
var path    = require('path');

var server  = express();
server.use(express.static(path.join(__dirname, 'public')));

server.listen(1337);
console.log("Server listening (PORT: " + 1337 + ") ...");

Any idea what to do, to keep the server running/find out what is the stopping reason?

Answer 1

When one connects remotely to a Pi using a remote client (eg. ssh, telnet, etc) then a shell is opened. Commands can be run in the background using the "&" (ampersand) operator. However, when one closes the client connection, all processes that were started from the shell and run in the background are sent the "hangup" signal indicating that the terminal that they ran from is no longer present. The majority of processes that receive the hangup signal terminate themselves. As such, if you start a process in the background and then terminate the remote client, the process you started will likely terminate itself.

Fortunately, there is a simple solution. Linux/Unix provides a shell command called "nohup" (see the man page on nohup for details). This command takes the command you want to run as a parameter. It causes the command you want to run to ignore hangup signals (presumably by receiving the hangup itself and ignoring it).

For example:

$ nohup myprogram param1 param2 &

will cause myprogram to run in the background and when you terminate the shell that started the program, it will continue to run even though the shell that started it is gone.

Answer 2

There's an npm package called "forever" you should try. I don't know about your specific problem, I don't think we have enough information to have a definitive answer, but I think you should look into that package. If the http server bonks it can restart it automagically, and you can hunt down the problem with some logging.