diff --git a/documentation/ref-manual/closer-look.xml b/documentation/ref-manual/closer-look.xml index d22de8fd99..a690544364 100644 --- a/documentation/ref-manual/closer-look.xml +++ b/documentation/ref-manual/closer-look.xml @@ -830,6 +830,97 @@ + +
+ Image Generation + + + Once packages are split and stored in the Package Feeds area, + the OpenEmbedded build system uses BitBake to generate the + root filesystem image: + + + + + The image generation process consists of several stages and + depends on many variables. + The do_rootfs uses these key variables + to help create the list of packages to actually install: + + IMAGE_INSTALL: + Lists out the base set of packages to install from + the Package Feeds area. + IMAGE_FEATURES: + Specifies features to include in the image. + These features map to additional packages for + installation. + PACKAGE_CLASSES: + Specifies the package manager to use and consequently + helps determine where to locate packages within the + Package Feeds area. + PACKAGE_EXCLUDE: + Specifies packages that should not be installed. + + + + + + In addition to the previously mentioned variables, the image + generation process uses + IMAGE_LINGUAS + to determine what language for which packages are being + installed. + + + + Part of the image generation process includes compressing the + root filesystem image. + Compression is accomplished through several optimization + routines designed to reduce the overall size of the image. + + + + The process runs as many post installation scripts as possible. + Any scripts that cannot be run are run when the system is + first booted. + If you are using a read-only root filesystem, all the post + installation scripts are run during the package installation + phase since the root filesystem cannot be written into. + + + + During the Prelink phase, optimization processes are run across + the image. + These processes include mklibs and + prelink. + The mklibs optimizes the size of the + libraries. + The prelink process optimizes the dynamic + linking of shared libraries to reduce start up time of the + executables. + See the + IMAGE_POSTPROCESS_COMMAND + and + ROOTFS_POSTPROCESS_COMMAND + variables for additional information. + + + + After the root filesystem has been constructed, the image + generation process turns everything into an image file or + a set of image files. + we need to turn into an image file or set of image files. + The formats used for the root filesystem depend on the + IMAGE_FSTYPES + variable. + + + + The entire image generation process is run under Pseudo. + Running under Pseudo ensures that the files in the root + filesystem have correct ownership. + +