You're reading from Mastering Embedded Linux Programming - Third Edition

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Published inMay 2021

PublisherPackt

ISBN-139781789530384

Edition3rd Edition

Concepts

Embedded Systems

Authors (2):

Frank Vasquez

Chris Simmonds

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Read-only compressed filesystems

Compressing data is useful if you don't have quite enough storage to fit everything in. Both JFFS2 and UBIFS do on-the-fly data compression by default. However, if the files are never going to be written, as is usually the case with the root filesystem, you can achieve better compression ratios by using a read-only compressed filesystem. Linux supports several of these: romfs, cramfs, and squashfs. The first two are obsolete now, so I will only describe SquashFS.

SquashFS

The SquashFS filesystem was written by Phillip Lougher in 2002 as a replacement for cramfs. It existed as a kernel patch for a long time, eventually being merged into mainline Linux in version 2.6.29 in 2009. It is very easy to use: you create a filesystem image using mksquashfs and install it to the flash memory:

$ mksquashfs rootfs rootfs.squashfs

The resulting filesystem is read-only, so there is no mechanism for modifying any of the files at runtime. The only way...

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Mastering Embedded Linux Programming - Third Edition

Published in: May 2021Publisher: PacktISBN-13: 9781789530384

Authors (2)

Frank Vasquez

Frank Vasquez is an independent software consultant specializing in consumer electronics. He has over a decade of experience designing and building embedded Linux systems. During that time, he has shipped numerous devices including a rackmount DSP audio server, a diver-held sonar camcorder, and a consumer IoT hotspot. Before his career as an embedded Linux engineer, Frank was a database kernel developer at IBM where he worked on DB2. He lives in Silicon Valley.
Read more about Frank Vasquez

Chris Simmonds

Chris Simmonds is a software consultant and trainer living in southern England. He has almost two decades of experience in designing and building open-source embedded systems. He is the founder and chief consultant at 2net Ltd, which provides professional training and mentoring services in embedded Linux, Linux device drivers, and Android platform development. He has trained engineers at many of the biggest companies in the embedded world, including ARM, Qualcomm, Intel, Ericsson, and General Dynamics. He is a frequent presenter at open source and embedded conferences, including the Embedded Linux Conference and Embedded World.
Read more about Chris Simmonds

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