[Buildroot] how does buildroot avoid requireing root?
john at stilen.com
Sat Jun 29 17:08:44 UTC 2013
That does answer my question very well.
On Sat, 2013-06-29 at 10:49 +0200, Thomas Petazzoni wrote:
> Dear John Stile,
> On Fri, 28 Jun 2013 17:47:16 -0700, John Stile wrote:
> > I am confused about how buildroot creates busybox.
> > There are notes that one must ensure that busybox setuid root.
> > Performing this operation must be performed as root:
> > chown 0.0 /bin/busybox; chmod 4755 /bin/busybox
> > Yet when I use buildroot I never become root.
> > How does buildroot accomplish this?
> > In output/build/busybox-1.18.5 I see applets/install.sh calls:
> > install -m 755 busybox $prefix/bin/busybox || exit 1
> > but I don't see how this becomes setuid?
> > On my embedded system, I see:
> > -rwsr-xr-x 1 root root 605876 Jun 28 2013 /bin/busybox*
> We use a combination of 'fakeroot' and 'makedevs'. From
> fakeroot runs a command in an environment wherein it
> appears to have root privileges for file
> manipulation. This is useful for allowing users to
> create archives (tar, ar, .deb etc.) with files in them
> with root permissions/ownership. Without fakeroot one
> would need to have root privileges to create the
> constituent files of the archives with the correct
> permissions and ownership, and then pack them up, or
> one would have to construct the archives directly,
> without using the archiver.
> fakeroot works by replacing the file manipulation library
> functions (chmod(2), stat(2) etc.) by ones that
> simulate the effect the real library functions would
> have had, had the user really been root. These wrapper
> functions are in a shared
> library /usr/lib/libfakeroot.so* which is loaded
> through the LD_PRELOAD mechanism of the dynamic loader.
> (See ld.so(8))
> Basically, we use fakeroot to run the following commands:
> tar cf rootfs.tar output/target
> And what makedevs does is that it reads some permission and device
> tables to create device files and adjust permissions. Those
> device/permission tables are constructed from system/device_table.txt
> (and system/device_table_dev.txt for devices) and also from individual
> package .mk files that use the <pkg>_PERMISSIONS and <pkg>_DEVICES
> mechanism. From package/busybox/busybox.mk:
> define BUSYBOX_PERMISSIONS
> /bin/busybox f 4755 0 0 - - - - -
> /usr/share/udhcpc/default.script f 755 0 0 - - - - -
> Here you see that we tell Buildroot to make Busybox a setuid binary.
> Does that answer your question?
> Best regards,
More information about the buildroot