This article explains how to install Debian on a Raspberry Pi. You will need to download the Debian distro prepared for the Pi. Get it from here:
Downloads
TIP: Use a fast SD card. They come rated:
| Class | Minimum Speed |
| Class 2 | 2 MB p/s |
| Class 4 | 4 MB p/s |
| Class 6 | 6 MB p/s |
| Class 10 | 10 MB p/s |
Next you will want to insert and unmount the SD card. It can’t be used while mounted. But you first need to know which “/dev/diskXXX” your SD card is found on. Try this:
Before inserting the SD card:
ls /dev/rdisk*
After inserting the SD card:
ls /dev/rdisk*
The difference between the above output will be the disk that you want to work with. Lets assume the SD card is found on “/dev/disk4”.
Unmount the disk as follows (assuming /dev/disk4″):
sudo diskutil unmount /dev/disk4s1
Now you want to “dd” the img file to the SD card:
sudo dd if=Downloads/2013-09-25-wheezy-raspbian.img of=/dev/rdisk4 bs=2m
In the above, you can see that i had downloaded the img file to my Downloads directory.
At this point you should be ready to put the SD card into the Pi and expect it to boot.