Simply Embedded

Note: the following post was originally published for Victoria Pi Makers and Friends as part of a presentation I prepared for the group. In this tutorial we are going to look at the filesystems on the Raspberry Pi and how they are used to boot Linux from an SD card. This is the only officially supported boot method available on the Raspberry Pi and... although this is specifically written with the Raspberry Pi in mind, many other boards can function in a similar fashion. To begin, we need to understand the basics of filesystems since the SD card contains several partitions with different types of filesystems. On Linux and Unix operating systems, the df utility can be used to check disk space, mount points and filesystem types, among other things. It is a very useful tool to know what filesystems are available and where each is mounted, as some of these may vary by distribution or platform. Running the df -Th (-Th tells df to display filesystem types and the size in human readable format respectively) command on the Raspberry Pi, we can see that there are several different filesystems mounted. Understanding the output of df is important to understand how Linux operates. The first thing to note from the output is there is a mount point called /boot. This existence of this mount point indicates that the device most likely booted off a filesystem. In many embedded systems, the operating system boots directly out of raw flash memory. Supporting a filesystem based approach makes it easier to upgrade and harder to brick. The user need only update the files on the SD card, reboot and off it goes. Now, you might be wondering how the Raspberry Pi booted off a filesystem. Well lets take a look. A filesystem is a piece of software, usually part of the OS (but not necessarily) that stores data onto some type of non-volatile memory. It translates generic operating system calls such as open/close/read/write etc into its own format and then stores the data on the media. There are many different types of filesystems, some of ...Read More