【整理】Buildroot生成的output/target下面的根文件系统rootfs不能直接使用：设备文件不是root权限

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 owernship/permissions properly even if Buildroot does not run

as root.