knochenreiter-buildroot/support/misc/target-dir-warning.txt

Warning!
========

This directory does *not* contain the root filesystem that you can use
on your embedded system. Since Buildroot does not run as root, it
cannot create device files and set the permissions and ownership of
files correctly in this directory to make it usable as a root
filesystem.

For that reason, do *not* use the contents of this directory to mount
your root filesystem over NFS or copy the contents of this directory
to a SD card or USB key, thinking it will work as the root filesystem
for your embedded system. It will simply *not* work.

Instead, if you need a usable root filesystem, please select one of
the filesystem image formats available in the Buildroot configuration
interface (make menuconfig or others) in the "Filesystem images"
sub-menu. If you want to get a filesystem image that you can easily
extract to your SD card or to some directory exposed through NFS,
please use the "tar the root filesystem" option. It will generate a
images/rootfs.tar image in your Buildroot output directory, which you
can extract as root:

  sudo tar -C /destination/of/extraction -xf images/rootfs.tar

Those image files are created using the contents of the target/
directory, but there is a post-processing step to create device files
and set ownership/permissions properly even if Buildroot does not run
as root.