// -*- mode:doc -*- ;
Customizing the generated target filesystem
Besides changing one or another configuration through +make *config+,
there are a few ways to customize the resulting target filesystem.
* Customize the target filesystem directly and rebuild the image. The
target filesystem is available under +output/target/+. You can
simply make your changes here and run make afterwards - this will
rebuild the target filesystem image. This method allows you to do
anything to the target filesystem, but if you decide to completely
rebuild your toolchain and tools, these changes will be lost. This
solution is therefore only useful for quick tests only: _changes do
not survive the +make clean+ command_. Once you have validated your
changes, you should make sure that they will persist after a +make
clean+ by using one of the following methods.
* Create a filesystem overlay: a tree of files that are copied directly
over the target filesystem after it has been built. Set
+BR2_ROOTFS_OVERLAY+ to the top of the tree. +.git+, +.svn+, +.hg+
directories, +.empty+ files and files ending with +~+ are excluded.
_Among these first 3 methods, this one should be preferred_.
* In the Buildroot configuration, you can specify the path to a
*post-build script*, that gets called 'after' Buildroot builds all the
selected software, but 'before' the rootfs packages are
assembled. The +BR2_ROOTFS_POST_BUILD_SCRIPT+ will allow you to
specify the location of your post-build script. This option can be
found in the +System configuration+ menu. The destination root
filesystem folder is given as the first argument to this script,
and this script can then be used to remove or modify any file in your
target filesystem. You should, however, use this feature with care.
Whenever you find that a certain package generates wrong or unneeded
files, you should fix that package rather than work around it with a
post-build cleanup script.
You may also use these variables in your post-build script:
- +BUILDROOT_CONFIG+: the path to the Buildroot .config file
- +HOST_DIR+, +STAGING_DIR+, +TARGET_DIR+: see
- +BINARIES_DIR+: the place where all binary files (aka images) are
- +BASE_DIR+: the base output directory
* Create your own 'target skeleton'. You can start with the default
skeleton available under +system/skeleton+ and then customize it to
suit your needs. The +BR2_ROOTFS_SKELETON_CUSTOM+ and
+BR2_ROOTFS_SKELETON_CUSTOM_PATH+ will allow you to specify the
location of your custom skeleton. These options can be found in the
+System configuration+ menu. At build time, the contents of the
skeleton are copied to output/target before any package
installation. Note that this method is *not recommended*, as it
duplicates the entire skeleton, which prevents from taking advantage
of the fixes or improvements brought to the default Buildroot
skeleton. The recommended method is to use the _post-build script_
mechanism described in the previous item.
Note also that if you want to perform some specific actions *after*
all filesystem images have been created (for example to automatically
extract your root filesystem tarball in a location exported by your
NFS server, or to create a special firmware image that bundles your
root filesystem and kernel image, or any other custom action), you can
specify a space-separated list of scripts in the
+BR2_ROOTFS_POST_IMAGE_SCRIPT+ configuration option.
Each of those scripts will be called with the path to the +images+
output directory as first and unique argument, and will be executed
with the main Buildroot source directory as the current
directory. Those scripts will be executed as the user that executes
Buildroot, which should normally not be the root user. Therefore, any
action requiring root permissions in one of these post-image script
will require special handling (usage of fakeroot or sudo), which is
left to the script developer.
Just like for the _post-build scripts_ mentioned above, you also have
access to the following environment variables from your _post-image
scripts_: +BUILDROOT_CONFIG+, +HOST_DIR+, +STAGING_DIR+, +TARGET_DIR+,
+BINARIES_DIR+ and +BASE_DIR+.