Category: BSD/Linux

Here’s a quick python script to use the camera you can attach to a Raspberry Pi and take a picture whenever it detects motion. This is pretty cool, there are all sorts of silly things you can do if you can do motion detection. And to do it with the Raspberry Pi and attached camera is relatively inexpensive (less than $100) to boot! Next time someone knocks our mailbox down we’ll have ’em!

I started from the script here and modified it to just take one picture to both test whether anything changed as well as save the picture if something changed. Seems a bit better than the original taking two pictures – at least this doesn’t cause the Pi to freeze. That means the Pi have to scan a bit larger image for a change but skipping pixels seems to keep it under control. It also takes better pictures as takes some time (the -t 500 in the raspistill call) to calibrate the camera.

#!/usr/bin/env python

import StringIO
import subprocess
import os
import time
from datetime import datetime
from PIL import Image

# Motion detection settings:
# Threshold (how much a pixel has to change by to be marked as "changed")
# Sensitivity (how many changed pixels before capturing an image)
# ForceCapture (whether to force an image to be captured every forceCaptureTime seconds)
threshold = 10
sensitivity = 2000
forceCapture = True
forceCaptureTime = 60 * 60 # Once an hour

# File settings
saveWidth = 1280
saveHeight = 960
diskSpaceToReserve = 500 * 1024 * 1024 # Keep 500 mb free on disk


# Capture a small test image (for motion detection)
def captureTestImage():
    command = "raspistill -w %s -h %s -t 500 -e bmp -o -" % (1280, 960)
    imageData = StringIO.StringIO()
    imageData.write(subprocess.check_output(command, shell=True))
    imageData.seek(0)
    im = Image.open(imageData)
    buffer = im.load()
    imageData.close()
    return im, buffer

# Keep free space above given level
def keepDiskSpaceFree(bytesToReserve):
    if (getFreeSpace() < bytesToReserve):
        for filename in sorted(os.listdir(".")):
            if filename.startswith("capture") and filename.endswith(".jpg"):
                os.remove(filename)
                print "Deleted %s to avoid filling disk" % filename
                if (getFreeSpace() > bytesToReserve):
                    return

# Get available disk space
def getFreeSpace():
    st = os.statvfs(".")
    du = st.f_bavail * st.f_frsize
    return du

# Get first image
image1, buffer1 = captureTestImage()

# Reset last capture time
lastCapture = time.time()

while (True):
    # Get comparison image
    image2, buffer2 = captureTestImage()

    # Count changed pixels
    changedPixels = 0

    for x in xrange(0, 1280, 4):
        for y in xrange(0, 960, 4):
            # Just check green channel as it's the highest quality channel
            pixdiff = abs(buffer1[x,y][1] - buffer2[x,y][1])
            if pixdiff > threshold:
                changedPixels += 1

    # Check force capture
    if forceCapture:
        if time.time() - lastCapture > forceCaptureTime:
            changedPixels = sensitivity + 1

    # Save an image if pixels changed
    if changedPixels > sensitivity:
        lastCapture = time.time()
        timeN = datetime.now()
        print "Save jpg"
        filename = "capture-%04d%02d%02d-%02d%02d%02d.jpg" % (timeN.year, timeN.month, timeN.day, timeN.hour, timeN.minute, timeN.second)
        image2.save(filename, "JPEG")
        keepDiskSpaceFree(bytesToReserve)
    # Swap comparison buffers
    image1 = image2
    buffer1 = buffer2
    time.sleep(2)
    print "Done waiting"

The one bit of switching to Debian that was difficult was setting up Exim and SMTP. I tried using the configuration off of FreeBSD but Debian just has it’s own special setup. For whatever reason the FreeBSD configuration resulted in SMTP reject errors.

This is a helpful command for debugging the exim configuration – it really helps to know what Exim4 is actually doing with all those config files!

exim -bP

So I tried the Debian approach and that worked ok for receiving mail (which the FreeBSD also did). However I still couldn’t connect with the mail client. Looking at it again if I’d read that wiki closely and followed all the instructions it would have saved me a couple of hours… I just needed to uncomment the SASL bit in /etc/exim4/exim4.conf.template. So always follow the instructions closely I suppose!

So the old server has always crashed quite a bit and been a bit slow for no obvious reason otherwise. So I spent some time trying to optimize the server with various things but then it occurred to me to consider this message on login:

### ZFS Tuning ###

ZFS is NOT tuned for instances with less than 1GB RAM.

For tuning 256MB and 512MB instances, the following link is recommended reading

http://wiki.freebsd.org/ZFSTuningGuide

I have to search for this periodically being sites like to change their SSL certificates every once and a while. So here’s another place to look for it!

If you don’t know what Fetchmail is its a little program (maybe its gigatic, I don’t know) that fetches email for you from many different email servers. This allows me to have one place where I store all my email across all my email addresses and then I can use an IMAP email server to view it all in one place. Very nice if you’ve many different email address.

In order to do this magic you have to tell fetchmail how to login to your email accounts and its always better to do this securely over SSL. To do it over SSL you have to tell fetchmail the site’s SSL certificiate (or you could weaken fetchmail to not care to validate the certificate but that seems silly). And to do that you have to tell it in hex or other computer sprach.

So first you need to get the SSL certificate in computer sprach:

openssl s_client -connect pop3.live.com:995 -showcerts | openssl x509 -fingerprint -noout -md5

Running this will get you the certificate computer sprach entry itself that’ll look something like this:

91:63:CF:6F:DF:03:3C:B9:3E:19:B3:1C:FF:EB:3C:25

Second you need to tell fecthmail to use this id when it connects to the server in the fetchmailrc file:

poll pop3.live.com uidl protocol POP3 user “xxxyyy@live.com” there with password “ohSuchASecurePassword!@#$” is xxxx@tttt here ssl sslfingerprint ‘91:63:CF:6F:DF:03:3C:B9:3E:19:B3:1C:FF:EB:3C:25‘

There you have it! That’s almost a good memorable, secure password I just made up there.

One sad day our old modem failed. The phone company gave us a new DSL modem/router. I had figured out how to setup portforwarding and such on the old modem. I can’t get into the new one at all! After briefly attempting to get info out of the phone company about how to access the new modem’s admin interface to no success I gave up on all my nice old port forwards.