Building Embedded Linux Systems

Chapter 8. Root Filesystem Setup

Having built the root filesystem and prepared the target’s storage device, we are now ready to set up the root filesystem as it will be used on the target. First, we need to select a filesystem type for the root filesystem. Then, we need to convert the root filesystem’s content to the selected filesystem format or install the root filesystem on a device formatted for the selected filesystem type.

This chapter begins by discussing the basic filesystem selection criteria. This is followed by a section describing how to use NFS to transfer filesystem images to the target’s flash, a technique we use often in this chapter. We then concentrate on the setup of root filesystems for use on CRAMFS, JFFS2, NFTL, and RAM disks, respectively. Finally, we discuss the use of TMPFS for mounting certain directories, and how to update an embedded system’s root filesystem dynamically. At the end of this chapter, the only issue remaining to getting a fully functional embedded system will be the setup and configuration of the bootloader. I will cover these issues in the next chapter.

Selecting a Filesystem

Selecting a filesystem type for your root filesystem is a delicate process. The final decision is often a compromise between the filesystem’s capabilities and the target’s purpose. It is, for example, useless to choose a filesystem that provides persistent write storage, such as JFFS2, if the target never needs to permanently store any data. For such a target, a filesystem ...