diff --git a/documentation/poky-ref-manual/ref-bitbake.xml b/documentation/poky-ref-manual/ref-bitbake.xml
index 6851fbf603..930b0a23f7 100644
--- a/documentation/poky-ref-manual/ref-bitbake.xml
+++ b/documentation/poky-ref-manual/ref-bitbake.xml
@@ -260,8 +260,50 @@
Once all the tasks have been completed BitBake exits.
-
+
+ When running a task, BitBake tightly controls the execution environment
+ of the build tasks to make sure unwanted contamination from the build machine
+ cannot influence the build.
+ Consequently, if you do want something to get passed into the build
+ task's environment, you must take a few steps:
+
+ Tell BitBake to load what you want from the environment
+ into the data store.
+ You can do so through the BB_ENV_WHITELIST
+ variable.
+ For example, assume you want to prevent the build system from
+ accessing your $HOME/.ccache directory.
+ The following command tells BitBake to load
+ CCACHE_DIR from the environment into the data
+ store:
+
+ export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE CCACHE_DIR"
+
+ Tell BitBake to export what you have loaded into the
+ environment store to the task environment of every running task.
+ Loading something from the environment into the data store
+ (previous step) only makes it available in the datastore.
+ To export it to the task environment of every running task,
+ use a command similar to the following in your
+ local.conf or distro configuration file:
+
+ export CCACHE_DIR
+
+
+
+
+
+ A side effect of the previous steps is that BitBake records the variable
+ as a dependency of the build process in things like the shared state
+ checksums.
+ If doing so results in unnecessary rebuilds of tasks, you can whitelist the
+ variable so that the shared state code ignores the dependency when it creates
+ checksums.
+ For information on this process, see the BB_HASHBASE_WHITELIST
+ example in Checksums (Signatures).
+
+