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[[full-rebuild]]
Understanding when a full rebuild is necessary
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A full rebuild is achieved by running:

---------------
$ make clean all
---------------

In some cases, a full rebuild is mandatory:

* each time the toolchain properties are changed, this includes:

** after changing any toolchain option under the _Toolchain_ menu (if
   the internal Buildroot backend is used);
** after running +make ctng-menuconfig+ (if the crosstool-NG backend
   is used);
** after running +make uclibc-menuconfig+.

* after removing some libraries from the package selection.

In some cases, a full rebuild is recommended:

* after adding some libraries to the package selection (otherwise,
  packages that can be optionally linked against those libraries
  won't be rebuilt, so they won't support those new available
  features).

In other cases, it is up to you to decide if you should run a
full rebuild, but you should know what is impacted and understand what
you are doing anyway.

[[rebuild-pkg]]
Understanding how to rebuild packages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

One of the most common questions asked by Buildroot users is how to
rebuild a given package or how to remove a package without rebuilding
everything from scratch.

Removing a package is unsupported by Buildroot without
rebuilding from scratch. This is because Buildroot doesn't keep track
of which package installs what files in the +output/staging+ and
+output/target+ directories, or which package would be compiled differently
depending on the availability of another package.

The easiest way to rebuild a single package from scratch is to remove
its build directory in +output/build+. Buildroot will then re-extract,
re-configure, re-compile and re-install this package from scratch. You
can ask buildroot to do this with the +make <package>-dirclean+ command.

For convenience, the special make targets
<package>-reconfigure and <package>-rebuild repeat the configure
resp. build steps.

However, if you don't want to rebuild the package completely from
scratch, a better understanding of the Buildroot internals is
needed. Internally, to keep track of which steps have been done and
which steps remain to be done, Buildroot maintains stamp files (empty
files that just tell whether this or that action has been done):

* +output/build/<package>-<version>/.stamp_configured+. If removed,
  Buildroot will trigger the recompilation of the package from the
  configuration step (execution of +./configure+).

* +output/build/<package>-<version>/.stamp_built+. If removed,
  Buildroot will trigger the recompilation of the package from the
  compilation step (execution of +make+).

Note: toolchain packages use custom makefiles. Their stamp files are named
differently.

Further details about package special make targets are explained in
xref:pkg-build-steps[].