Run Python script in the background as a service in raspberry pi on boot

This is a simple service in Python and need it to start running in the background when the Raspberry Pi boots. Here Python script receive udp data in real time. The following init script makes getting a Python script (or e.g. a Perl script) to run when the Raspberry Pi boots fairly painless. Services are supposed to run as "daemons" which is quite complicated in Python. We use start-stop-daemon command to run our script in the background and basically deals with everything we need.

This is init file save it as myservice.sh at

 /etc/init.d   

 #!/bin/sh 
 ### BEGIN INIT INFO 
 # Provides:     myservice 
 # Required-Start:  $remote_fs $syslog 
 # Required-Stop:   $remote_fs $syslog 
 # Default-Start:   2 3 4 5 
 # Default-Stop:   0 1 6 
 # Short-Description: Put a short description of the service here 
 # Description:    Put a long description of the service here 
 ### END INIT INFO 
 # Change the next 3 lines to suit where you install your script and what you want to call it 
 DIR=/usr/local/bin/myservice 
 DAEMON=$DIR/myservice.py 
 DAEMON_NAME=myservice 
 # Add any command line options for your daemon here 
 DAEMON_OPTS="" 
 # This next line determines what user the script runs as. 
 # Root generally not recommended but necessary if you are using the Raspberry Pi GPIO from Python. 
 DAEMON_USER=root 
 # The process ID of the script when it runs is stored here: 
 PIDFILE=/var/run/$DAEMON_NAME.pid 
 . /lib/lsb/init-functions 
 do_start () { 
   log_daemon_msg "Starting system $DAEMON_NAME daemon" 
   start-stop-daemon --start --background --pidfile $PIDFILE --make-pidfile --user $DAEMON_USER --chuid $DAEMON_USER --startas $DAEMON -- $DAEMON_OPTS 
   log_end_msg $? 
 } 
 do_stop () { 
   log_daemon_msg "Stopping system $DAEMON_NAME daemon" 
   start-stop-daemon --stop --pidfile $PIDFILE --retry 10 
   log_end_msg $? 
 } 
 case "$1" in 
   start|stop) 
     do_${1} 
     ;; 
   restart|reload|force-reload) 
     do_stop 
     do_start 
     ;; 
   status) 
     status_of_proc "$DAEMON_NAME" "$DAEMON" && exit 0 || exit $? 
     ;; 
   *) 
     echo "Usage: /etc/init.d/$DAEMON_NAME {start|stop|restart|status}" 
     exit 1 
     ;; 
 esac 
 exit 0 

Then create myservice.py file at /usr/local/bin/myservice . and also create output.txt file in the same directory. change permission by chmod 777 myservice.py

 import sys, struct  
 from socket import *  
 SIZE = 1024   # packet size  
 hostName = gethostbyname('0.0.0.0')  
 mySocket = socket( AF_INET, SOCK_DGRAM )  
 mySocket.bind((hostName,18736))  
 repeat = True  
 while repeat:  
   (data,addr) = mySocket.recvfrom(SIZE)  
   data = struct.unpack('d',data)  
   data=int(data[0])  
   file = open("output.txt", "w")  
   file.write(str(data))  
   file.close()  

To run this when raspberry pi boot

 sudo nano /etc/rc.local  

:

then add bellow line before exit line in rc.local 

 sudo /etc/init.d/myservice.sh start  

you can also manually start your Python script using the command

 sudo /etc/init.d/myservice.sh start  

check its status with the

 sudo /etc/init.d/myservice.sh status  

stop it with

 sudo /etc/init.d/myservice.sh stop   

Run script at boot as service

This is achieved using the init run-level based rc scripts. Basically the command "service" used to start and stop system services. for example "service <your script> start".

  # update boot / reboot files   
  sudo cp <your script> /etc/init.d/ # <your script> your script file with the path   
  # do it as soon as the device is going down,   
  # both for shutdown and reboot   
  sudo chmod u+x <your script>   
  sudo update-rc.d /etc/init.d/<your script> defaults   

The <your script> is : 

   #! /bin/sh   
   ### BEGIN INIT INFO   
   # Provides:   <your script name>   
   # Required-Start: $all   
   # Required-Stop:    
   # Default-Start:  2 3 4 5   
   # Default-Stop:  0 1 6   
   # Short-Description: Manage my cool stuff   
   ### END INIT INFO   
   PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/bin   
   . /lib/init/vars.sh   
   . /lib/lsb/init-functions   
   # If you need to source some other scripts, do it here   
   case "$1" in   
   start)   
    log_begin_msg "Starting my super cool service"   
   # do something   
    log_end_msg $?   
    exit 0   
    ;;   
   stop)   
    log_begin_msg "Stopping the coolest service ever unfortunately"   
    # do something to kill the service or cleanup or nothing   
    log_end_msg $?   
    exit 0   
    ;;   
   *)   
    echo "Usage: /etc/init.d/<your script> {start|stop}"   
    exit 1   
    ;;   
   esac   

Then replace # do something with the content of your original script. for example : 
 

 sudo service hostapd stop  
 sudo service udhcpd stop  
 sudo service hostapd start  
 sudo service udhcpd start   

Simulink with Matlab

In the MATLAB command window enter the command               
                    

            >> simulink

The alternate method is to click the Simulink icon in the MATLAB toolbar

  A Simulink library window will pop up as shown below :

 

Introduction to Simulink in MATLAB

Simulink (Simulation and link) is developed by MathWorks as an add-on with MATLAB. It is a graphical programming language which offers modelling, simulation and analyzing of multi domain dynamic systems under Graphical User Interface (GUI) environment. The Simulink have tight integration with the MATLAB environment and have a comprehensive block libraries and toolboxes for linear and nonlinear analyses. The system models can be so easily constructed via just click and drag operations. The Simulink comes handy while dealing with control theory and model based design.

Receive data from a Simulink's built-in "UDP Send" block in python

 import sys, struct  
 import time  
 from socket import *  
 SIZE = 1024   # packet size  
 hostName = gethostbyname('0.0.0.0')  
 mySocket = socket(AF_INET,SOCK_DGRAM)  
 mySocket.bind((hostName,18726))  
 repeat = True  
 while repeat:  
   (data,addr) = mySocket.recvfrom(SIZE)  
   data = struct.unpack('d',data)  
   print int(data[0])  

List no of bluetooth devices that are connected to raspberry pi

 import bluetooth  
 print("performing inquiry...")  
 nearby_devices = bluetooth.discover_devices(lookup_names = True)  
 print("found %d devices" % len(nearby_devices))  
 for addr, name in nearby_devices:  
   print(" %s - %s" % (addr, name))  

Check availability of a device via bluetooth in raspberry pi

 #!/usr/bin/python  
 import bluetooth  
 import time  
 while True:  
   print "Checking " + time.strftime("%a, %d %b %Y %H:%M:%S", time.gmtime())  
   result = bluetooth.lookup_name('1C:66:AA:CF:DD:35', timeout=5)  
   if (result != None):  
     print "Available"  
   else:  
     print "Not Available"  
   time.sleep(60)  

Audio Slicing in python

Divide the audio file into no of sample by time interval and then play.

 import wave  
 import pygame  
 import time  
 import sys  
 def slice(infile, outfilename, start_ms, end_ms):  
   width = infile.getsampwidth() #Returns sample width in bytes  
   rate = infile.getframerate() #Returns sampling frequency  
   fpms = rate / 1000 # frames per ms  
   length = (end_ms - start_ms) * fpms  
   start_index = start_ms * fpms  
   out = wave.open(outfilename, "w")  
   out.setparams((infile.getnchannels(), width, rate, length, infile.getcomptype(), infile.getcompname()))  
   infile.rewind()       #Rewind the file pointer to the beginning of the audio stream  
   anchor = infile.tell()   #Return current file pointer position  
   infile.setpos(anchor + start_index) #Set the file pointer to the specified position  
   out.writeframes(infile.readframes(length)) #Write audio frames and make sure nframes is correct  
 if __name__ == "__main__":  
   slice(wave.open("song1.wav", "r"), "out.wav", int(sys.argv[1]), int(sys.argv[2]))  
   pygame.mixer.init()  
   pygame.mixer.music.load("out.wav")  
   pygame.mixer.music.play()  
   while pygame.mixer.music.get_busy() == True:  
     continue