Книга: Embedded Linux Primer: A Practical, Real-World Approach

6.1.4. The Root FS Challenge

6.1.4. The Root FS Challenge

The challenge of a root file system for an embedded device is simple to explain. It is not so simple to overcome. Unless you are lucky enough to be developing an embedded system with a reasonably large hard drive or large Flash storage on board, you might find it difficult to fit your applications and utilities onto a single Flash memory device. Although costs continue to come down for Flash storage, there will always be competitive pressure to reduce costs and speed time to market. One of the single largest reasons Linux continues to grow in popularity as an embedded OS is the huge and growing body of Linux application software.

Trimming a root file system to fit into a given storage space requirement can be daunting. Many packages and subsystems consist of dozens or even hundreds of files. In addition to the application itself, many packages include configuration files, libraries, configuration utilities, icons, documentation files, locale files related to internationalization, database files, and more. The Apache web server from the Apache Software Foundation is an example of a popular application often found in embedded systems. The base Apache package from one popular embedded Linux distribution contains 254 different files. Furthermore, they aren't all simply copied into a single directory on your file system. They need to be populated in several different locations on the file system for the Apache application to function without modification.

These concepts are some of the fundamental aspects of distribution engineering, and they can be quite tedious. Linux distribution companies such as Red Hat (in the desktop and enterprise market segments) and Monta Vista Software (in the embedded market segment) spend considerable engineering resources on just this: packaging a collection of programs, libraries, tools, utilities, and applications that together make up a Linux distribution. By necessity, building a root file system employs elements of distribution engineering on a smaller scale.

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