Changing the hostname on your raspberry pi

By default, the hostname on a raspberry pi installation will be “raspberrypi”, which is great if you just have the one pi.

Two raspberry pis, one with a BrickPi attached for controlling lego mindstorms

Two raspberry pis, one with a BrickPi attached for controlling lego mindstorms

If you’ve got more than one, then you’re going to get hostname conflicts when you attach both to your network. Fortunately its easy to correct this.

Plug the pi that you want to change hostname onto the network (leave the other unattached). That way when you ssh onto raspberrypi, you know which one it is.

Next, edit the hosts file.

sudo nano /etc/hosts

You’ll need to change the last line to whatever you want to name the pi, in my case I called it robopi

127.0.0.1       localhost
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

127.0.1.1       robopi

Exit that file and then change the hostname file

sudo nano /etc/hostname

Change it to the same name you put in the hosts file

robopi

Thats the configuration changes done, next we need to restart the hostname service, but executing:

sudo /etc/init.d/hostname.sh

Then restart the pi

sudo reboot

After that, you should be able to ping and connect to robopi:

Jamess-MacBook-Pro:pi Elsey$ ping robopi
PING robopi.home (192.168.0.10): 56 data bytes
64 bytes from 192.168.0.10: icmp_seq=0 ttl=64 time=1.802 ms
64 bytes from 192.168.0.10: icmp_seq=1 ttl=64 time=4.141 ms
^C
--- robopi.home ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 1.802/2.971/4.141/1.170 ms
Jamess-MacBook-Pro:pi Elsey$ ssh pi@robopi
pi@robopi's password: 
Linux robopi 3.6.11+ #456 PREEMPT Mon May 20 17:42:15 BST 2013 armv6l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sun Dec 29 15:59:40 2013 from unknown
-bash: /etc/profile: is a directory
pi@robopi ~ $ hostname
robopi 

Thats it, you can connect the original “raspberrypi” to the network, or change the hostname of that too

Robots! (part 1)

Inspired by the android controlled lego robots I saw at DroidCon UK this year, and with difficulty finding a use for my raspberry pi, I’ve decided to have a go at building a robot that I can control via an android app. Having a 24 hour flight home from Australia at the weekend, I’ve had plenty of time to think about how I might approach this task (or challenge as I refer to it as I’ve no prior experience with robotics / socket programming).

Lego robot powered by the BrickPi

My plan is to have a python socket server running on the pi. This will provide a socket that an android client can invoke commands on. This python server will also interact with the python scripts that the BrickPi uses to control lego motors.

Whilst most of my experience revolves around Java, I’ve opted for python for the following reasons

  • Python is supported on the pi out of the box, no need to mess around with installing Java
  • The BrickPi has support for Python (and C)
  • I feel like learning something new

Baby steps…

Starting simple, I thought it best to create a simple script that listens on a socket, and then create a client that sends it some data to print out to the console. Once I have this working I can expand on it and make the client more sophisticated (an android app for example) and also enhance the server so it can handle different types of commands.

Server
There are plenty of example python scripts online, I found a good one here and tweaked it slightly to remove the parts I don’t want. (full credit to pythonadventures!)

#!/usr/bin/env python
# server.py

import socket
import select
import Queue
from threading import Thread
import sys

class ProcessThread(Thread):
    def __init__(self):
        super(ProcessThread, self).__init__()
        self.running = True
        self.q = Queue.Queue()

    def add(self, data):
        self.q.put(data)

    def stop(self):
        self.running = False

    def run(self):
        q = self.q
        while self.running:
            try:
                # block for 1 second only:
                value = q.get(block=True, timeout=1)
                process(value)
            except Queue.Empty:
                sys.stdout.write('.')
                sys.stdout.flush()
        #
        if not q.empty():
            print "Elements left in the queue:"
            while not q.empty():
                print q.get()

t = ProcessThread()
t.start()

def process(value):
    print value

def main():
    s = socket.socket()
    host = socket.gethostname()
    port = 3033
    s.bind((host, port))

    print "Server listening on port {p}...".format(p=port)

    s.listen(5)                 # Now wait for client connection.

    while True:
        try:
            client, addr = s.accept()
            ready = select.select([client,],[], [],2)
            if ready[0]:
                data = client.recv(4096)
                t.add(data)
        except KeyboardInterrupt:
            print
            print "Stopping server."
            break
        except socket.error, msg:
            print "Socket error %s" % msg
            break

    cleanup()

def cleanup():
    t.stop()
    t.join()

if __name__ == "__main__":
    main()

The socket is bound to a port, and then continually listens for incoming data. Once some data is received, it is added onto a queue, which is then sequentially executed.

Client
The client is is fairly straightforward, it involves opening a connection on a socket and writing data to it, a few lines of Java code.

public static void main(String[] args) throws IOException {

        InetAddress address = InetAddress.getLocalHost();
        Socket socket = new Socket(address, 3033);

        BufferedOutputStream bos = new BufferedOutputStream(socket.getOutputStream());

        OutputStreamWriter osw = new OutputStreamWriter(bos, "US-ASCII");

        System.out.println("Sending message...");

        osw.write("Hello!");
        osw.flush();
    }

Thats it for now, you can checkout my code on github (or just copy/paste the above) and run the client and server and see it in action.

I’ll start on the client next..