netcat to run remote script

actmnophn · 03-13-2014, 06:03 PM

I am having trouble finding this because I am not sure what to look for. I want to execute a command on another machine on my local network. I do want to use ssh because there is a little(? 5sec) delay until the command gets sent.
I have seen commands sent to servers vi netcat to a server. I was wondering if/how to set up a script as a aimple server to listen for a small set of commands and execute commands based on nc inpuut.
Thanks

--edit:
I am looking in the direction of nc -l -k -p 12345 -e ~/myscript.sh but I am not sure of 2 points. How to keep it listening (-k did not seem to work when i tried it with -e /bin/bash). And how to make the script listen to input (Its a local network so its not the end of the world if I use -e /bin/bash)

Ser Olmy · 03-13-2014, 06:44 PM

I guess you could use a script to pull data from nc and execute them with eval, but it'd be bloody dangerous. Why is the ssh delay such a big deal? Do you need to run the command(s) at a specific time, right down to the second?

(I'll readily admit that the idea of using netcat to send commands to a remote server would never, ever have occurred to me.)

actmnophn · 03-13-2014, 07:27 PM

I am using gpio input from raspberry pi to play a sound on another machine on a local (no internet yes wifi not bullet-proof) network when a button is pressed and ssh is a few seconds off. Imagine a doorbell that lags 5 seconds not the end of the world but very annoying.
Another idea I came up with is to keep open an ssh connection and send the commands that way.

Ser Olmy · 03-13-2014, 09:36 PM

I see your point, and just for fun, this netcat script will work (for very particular values of 'work'):

Code:

#!/bin/sh
while true ; do
  x=$(nc -l -q 0 -p 54321)
  eval $x
done

54321 is the port number. To send a command to the server running this script, do this (or not, please):

Code:

user@linux:~$ echo <command> | nc -q 0 <IP_address_of_server> 54321

If the <command> is break, the server script will terminate.

Remember that anyone with access to the network will:

a) be able to send any command to your server, and
b) may be able to spy on the commands you're sending.

If you just want to run a limited set of commands, it would make more sense to send a simple number or identifier, and have the script interpret that as "run command X". It would vastly improve security too.

chrism01 · 03-14-2014, 02:00 AM

Would an ssh tunnel work; ie set it up in advance, then use on demand?

actmnophn · 03-15-2014, 09:56 PM

I think it would. I'm not sure how to implement though. I tried searching but could not word the search the right way to find anything helpful enough. I am going to work on using eval meanwhile because I dont really need to open up everything it will be like a mini server and respond to specific keywords that are defined in a script on the server side to represent commands.
Thanks