How to control multiple raspberry pi's at once over ethernet?

Question

My mac is connected to four raspberry pi's using a desktop switch. My mac has ip 192.168.1.90 and my RPi's 192.168.1.11, 192.168.1.12, 192.168.1.13, 192.168.1.14. I can control them via ssh using the terminal on my mac, e.g. ssh pi@192.168.1.11 and can have four terminal screens open to control each one of them.

I would like to sent the same command (to control the camera) to each of the four raspberry pi's at the same time. Instead of copy pasting the command to the four terminal windows, would it be possible to somehow control the four pi's at the same time in one terminal window?

Answer 1

There is MQTT, a publish/subscribe messaging system. Under Linux it seems to be supported by the mosquitto package.

apt-cache search mosquitto
libmosquitto-dev - MQTT version 3.1 client library, development files
libmosquitto1 - MQTT version 3.1 client library
libmosquittopp-dev - MQTT version 3.1 client C++ library, development files
libmosquittopp1 - MQTT version 3.1 client C++ library
mosquitto - MQTT version 3.1/3.1.1 compatible message broker
mosquitto-clients - Mosquitto command line MQTT clients
mosquitto-dbg - debugging symbols for mosquitto binaries
python-mosquitto - MQTT version 3.1 Python client library
python3-mosquitto - MQTT version 3.1 Python 3 client library
libmosquitto0 - MQTT version 3.1 client library
libmosquitto0-dev - MQTT version 3.1 client library, development files
libmosquittopp0 - MQTT version 3.1 client C++ library
libmosquittopp0-dev - MQTT version 3.1 client C++ library, development files

That would allow you to publish the event (take photo) on one machine and have your Pi's subscribed to that event.

This would be a programming solution. I'm not sure if there is a bash interface to the publish/subscribe methods.

I HAVE NOT used it. I'm aware of it simply because I see it often recommended for this sort of task.

You give no indication of any timing constraints, e.g. how closely the photos must be synchronised in time.

EDITED TO ADD

I have had a quick play with mosquitto

sudo apt-get install python-mosquitto # on server and clients
sudo apt-get install mosquitto # only needed on server

I wrote a couple of scripts.

The server tells the clients when to take the photos (now or some time in the future).

The clients wait for the specified time and then take the photo (actually it prints diagnostics).

A webm video here

Server Python script

#!/usr/bin/env python

import mosquitto
import time

mq = mosquitto.Mosquitto()

# Connect to mercury
mq.connect("mercury")

# Take a photo now
t = time.time()
print("take photo at {}".format(t))
mq.publish("photo/trigger", "{}".format(t))

time.sleep(1)

# Take a photo in 10 seconds
t = time.time() + 10
print("take photo at {}".format(t))
mq.publish("photo/trigger", "{}".format(t))

time.sleep(11)

# Take a photo in 5 seconds
t = time.time() + 5
print("take photo at {}".format(t))
mq.publish("photo/trigger", "{}".format(t))

time.sleep(6)

# Take a photo now
t = time.time()
print("take photo at {}".format(t))
mq.publish("photo/trigger", "{}".format(t))

Client Python script

#!/usr/bin/env python

import mosquitto
import time

def on_connect(mosq, obj, msg):
   print "Connected"

def on_message(mosq, obj, msg):
   msg_time = time.time()
   snap_time = float(msg.payload)
   while time.time() < snap_time:
      pass
   now_time = time.time()

   print ("msg={}, snap={}, now={}".format(msg_time, snap_time, now_time))

mq = mosquitto.Mosquitto()

#define callbacks
mq.on_message = on_message
mq.on_connect = on_connect

#connect
mq.connect("mercury")

#subscribe to topic 
mq.subscribe("photo/trigger")

#keep connected to broker
while mq.loop() == 0:
   pass

Answer 2

If you're asking about controlling the Pi's camera module specifically (as opposed to something like a USB webcam), you might want to have a look at my compoundpi project which was built for this purpose (it'll handle 4 quite happily; I originally made it for a group at the local university which had 20!).

It includes a console and GUI client which should work on Mac (it's all written in Python; the console client should work "out of the box" on Mac but the GUI client will involve installing the PyQt4 bindings). There's also a Python-based client library for scripting.

At the moment, the client has only been tested on Linux (Ubuntu) and Windows (works, but it's a pain to install). I'd be interested to hear of Mac experiences!

Answer 3

The simplest way would be to create some kind of a Bash script on your Mac, if you are running bash.

for i in 11 12 13 14; do ssh pi@192.168.1.$i "your command here"; done

Maybe some kind of a terminal multiplexer which allows you to send a command to all shells? For instance, on Windows I use Putty, and a tool called "MTPutty" that wraps multiple putty into tabs in the same window, and there's an option to send a script to all Putty sessions simultaneously.

Personally, I would go with the scripting option. Even create a shell script maybe.

Answer 4

clusterssh allows you to connect via SSH to multiple servers and send the same commands to each one :

You could also use a terminal emulator that supports groups, such as terminator