Python not executing shell script

[dchurch24]

Hi all,

I have a python script that listens on an IP port and executes a given command.

The commands are looked up in a MySQL database and then sent to the tcp python server. There are multiple 'servers' running on the network.

However, I have a compiled program called ADU which executes fine - in turn the ADU unit switches a relay and turns a specified device on (lamps, amplifiers etc...)

I have another usb relay that isn't an ADU one and the script to execute it is:

echo -e 'xff\x02\x01' > /dev/ttyUSB0

This works fine from terminal, but does not run from inside Python.

Ok, I thought, I'll wrap it up in a script, so I have a script called SwitchR1.sh with the command above inside it and nothing else.

It doesn't execute either?!?

The python code is:



import commands
import os, subprocess

class EchoRequestHandler(SocketServer.BaseRequestHandler ):
def setup(self):
print self.client_address, 'connected!'
self.request.send('hi ' + str(self.client_address) + '\n')

def run_command(self,cmd):
#os.system(cmd)
subprocess.call(cmd,shell=True)
print cmd

def handle(self):
data = 'dummy'
while data:
data = self.request.recv(1024)
self.request.send(data)
if data.strip() == 'bye':
return
self.run_command(data.strip())

def finish(self):
print self.client_address, 'disconnected!'
self.request.send('bye ' + str(self.client_address) + '\n')

#server host is a tuple ('host', port)
server = SocketServer.ThreadingTCPServer(('', 50002), EchoRequestHandler)
server.serve_forever()


I have tried os.system(cmd) as well, as can be seen in the commented line.

The correct command prints out to the screen so I know the IP bit is working and recieving the correct command. It just doesn't execute.

I have made sure that the user running the IP listener is the same owner of the scripts too, just in case it was a permissions error.

I can send commands such as "ls -l" etc... and they execute fine.

Does anyone know why this isn't working?

[dchurch24]

Ok, I've just changed the script to run 'ls -l' and it runs it fine, so Python is executing the script ok.

I then thought maybe it was something to do with 'echo' (clutching at straws here) and so I did 'echo "hello" - and that worked too.

So it seems it's to do with the echo to /dev/ttyUSB0 for some reason.

[iponeverything]

try su'ing to uid of the listener and trying the echo to the dev.

[dchurch24]

Woooaaahh! Thanks for the quick reply - but I don't know how to do what you just said to do :-)

I don't suppose you could give me a quick example.

I am so close to getting all this working - this is really frustrating, it's the last 'hurdle'

[iponeverything]

ps auxwww|grep <name of your listener>

The name in the first column will be who your process is running as. Say its "www-data" for example..

then change to that user:



sudo bash
su - www-data
echo -e 'xff\x02\x01' > /dev/ttyUSB0


If it fails, your listening process is not allowed to write to the device.

[dchurch24]

Thanks very much for that - sadly, it works when I do that, which means that the user DOES have rights to run that command.

I'm REALLY lost now!

[dchurch24]

I have, however, now noticed that the rx and tx lights on the USB->Serial card are flashing, which means that the script actually is executing.

It's just not switching any of the relays...yet it does when I run the script manually.

Really odd.

[dchurch24]

Hmmm...get somewhere. slooooowwwlly.

if I send:

sock.send("echo -e '\xff\x01\x01' > /dev/ttyUSB0")

to the listener from the client, it works.

If I send:

sock.send("echo -e '\xff\x01\x00' > /dev/ttyUSB0")

Then I get the following error on the server:

----------------------------------------
('192.168.1.4', 49923) connected!
----------------------------------------
Exception happened during processing of request from ('192.168.1.4', 49923)
Traceback (most recent call last):
File "/usr/lib/python2.5/SocketServer.py", line 464, in process_request_thread
self.finish_request(request, client_address)
File "/usr/lib/python2.5/SocketServer.py", line 254, in finish_request
self.RequestHandlerClass(request, client_address, self)
File "/usr/lib/python2.5/SocketServer.py", line 522, in __init__
self.handle()
File "tcpserver.py", line 22, in handle
self.run_command(data.strip())
File "tcpserver.py", line 12, in run_command
subprocess.call(cmd,shell=True)
File "/usr/lib/python2.5/subprocess.py", line 444, in call
return Popen(*popenargs, **kwargs).wait()
File "/usr/lib/python2.5/subprocess.py", line 594, in __init__
errread, errwrite)
File "/usr/lib/python2.5/subprocess.py", line 1147, in _execute_child
raise child_exception
TypeError: execv() arg 2 must contain only strings
----------------------------------------

This is making me think that python doesn't like the ' or \ characters - do I need to escape this?

EDIT: I have tried escaping the chars, but it's still not sending the correct string to the USB device.