Last time, we setup the Raspberry Pi so it could read the values from some DS18B20 sensors using the command line tool owfs. We’re a still few steps away from publishing these temperatures to Emoncms at the moment – namely getting owfs to start automatically, reading the values in Python, and then publishing them.

Running owfs automatically

When building owfs from source, you don’t get automatic startup as an option. It is quite easy to setup though.

First, let’s build a config file to store settings:

sudo nano /etc/owfs.conf

And copy and paste this in:

# owfs will source temperatures from this device
owfs: device=/dev/i2c-1

# file system location
mountpoint = /mnt/1wire
allow_other

It is important to note that this setup means that only owfs can access the 1-Wire bus. The default configuration is to run owserver and then have all other ow* processes connect to owserrver – i.e. it distributes the data. I want to keep my setup as simple as possible, so owfs connects directly to the bus.

Let’s test this config out:

pi@raspberrypi2 /etc/init.d $ sudo /opt/owfs/bin/owfs -c /etc/owfs.conf
pi@raspberrypi2 /etc/init.d $ ls /mnt/1wire
28.33F749050000  28.79774A050000  28.EDEE49050000  bus.0     simultaneous  structure  uncached
28.3474A3040000  28.DB564A050000  alarm            settings  statistics    system
pi@raspberrypi2 /etc/init.d $

Now we need to create an init script:

sudo nano /etc/init.d/owfs

And then copy and paste this into the file:

#! /bin/sh
case "$1" in
  start)
        /opt/owfs/bin/owfs -c /etc/owfs.conf
        ;;
  stop)
        killall owfs
        ;;
  *)
        echo "Usage: $N {start|stop}" >&2
        exit 1
        ;;
esac
exit 0

This is totally barebones, but I always use this form of init script and it works well.

Now make it executable:

sudo chmod 755 /etc/init.d/owfs

Then use the very convenient tool, update-rc.d to add links so that this script runs at the appropriate times and runlevels:

sudo update-rc.d /etc/init.d/owfs defaults

Then restart your Pi:

sudo shutdown -r now

Once restarted, check everything is running and you can still see the devices:

pi@raspberrypi2 ~ $ ps aux | grep owfs
root      2175  0.0  0.2  28416  1136 ?        Ssl  23:48   0:00 /opt/owfs/bin/owfs -c /etc/owfs.conf
pi        2340  0.0  0.1   3544   808 pts/0    S+   23:50   0:00 grep --color=auto owfs
pi@raspberrypi2 ~ $ ls /mnt/1wire
28.33F749050000  28.79774A050000  28.EDEE49050000  bus.0     simultaneous  structure  uncached
28.3474A3040000  28.DB564A050000  alarm            settings  statistics    system
pi@raspberrypi2 ~ $