https://wiki.yoctoproject.org/wiki/index.php?action=history&feed=atom&title=Poky_NFS_RootPoky NFS Root - Revision history2026-04-18T23:54:58ZRevision history for this page on the wikiMediaWiki 1.39.5https://wiki.yoctoproject.org/wiki/index.php?title=Poky_NFS_Root&diff=115&oldid=prevScottrif: Created page with '= HOWTO: Booting poky images on hardware from network = == Overview == Booting from network is a common practice when developing embedded system on real hardware. It avoids the …'2010-10-22T22:25:18Z<p>Created page with '= HOWTO: Booting poky images on hardware from network = == Overview == Booting from network is a common practice when developing embedded system on real hardware. It avoids the …'</p>
<p><b>New page</b></p><div>= HOWTO: Booting poky images on hardware from network =<br />
<br />
== Overview ==<br />
Booting from network is a common practice when developing<br />
embedded system on real hardware. It avoids the time consuming<br />
process of downloading the kernel and root filesystem to a hard<br />
drive or flash to make developer's life easier.<br />
<br />
The general idea is to use a bootloader to get the kernel<br />
image (using TFTP, mostly) and specifying nfsroot in the kernel<br />
command line to mount rootfs via a remote NFS server. In the<br />
case of x86 systems, the bootloader is usually PXE (Preboot<br />
Execution Environment), either provided by BIOS or other PXE<br />
implementations like gPXE.<br />
<br />
This HOWTO walks through the process of setting everything<br />
for eMenlow, with NFS-root, you can:<br />
* boot a diskless and flashless target<br />
* avoid downloading kernel/rootfs after a rebuild<br />
* change files on the fly even on read-only fs (jffs2, squashfs, etc.)<br />
* boot on different boards or boxen<br />
<br />
== Target bootloading with gPXE ==<br />
<br />
''''' TODO: integrate gPXE into yocto '''''<br />
<br />
The traditional method of bootloading is the PXE stack provided in BIOS.<br />
However, that often requires DHCP cooperation, which is not viable in many<br />
circumstances. Here we use gPXE, an open-source PXE implementation, to get<br />
around this DHCP restriction.<br />
<br />
It can function as a standalone bootloader or be chainloaded by grub. Since<br />
it's less than 500kB in size, it can fit in a small USB flash drive very well.<br />
<br />
First, build it from source. Suppose your development machine has the hostname<br />
of '''<hostname>''':<br />
<br />
$ git clone git://git.etherboot.org/scm/gpxe.git<br />
$ cd gpxe<br />
$ cat > chainload.gpxe <<EOF<br />
#!gpxe<br />
dhcp net0<br />
kernel tftp://<hostname>/boot.gpxe<br />
boot<br />
EOF<br />
$ cd src<br />
$ EMBEDDED_IMAGE=../chainload.gpxe make bin/gpxe.usb<br />
<br />
The '''EMBEDDED_IMAGE''' is the builtin script as gPXE starts. The script above<br />
chainloads another gPXE script on the remote tftp server (your development machine)<br />
to get actual kernel and rootfs image location.<br />
<br />
After that, bin/gpxe.usb can be written to an empty USB stick to bootload the<br />
image on any box that has a network connection:<br />
<br />
'''''warning: the content of the usb device will be wiped out!'''''<br />
<br />
# dd if=bin/gpxe.usb of=</dev/sdX><br />
<br />
Alternatively, there are also other targets available, for example, bin/gpxe.lkrn<br />
can be built to be chainloaded by grub, please refer to gPXE docs.<br />
<br />
== Development box preparation ==<br />
<br />
'''''TODO: integrate nfs server and tftpd into yocto'''''<br />
<br />
To set up tftp and nfs server on debian/ubuntu, simply:<br />
<br />
# apt-get install nfs-kernel-server atftpd<br />
<br />
tftpd-hpa can be used as well instead of atftpd.<br />
<br />
== Target system changes ==<br />
There are two additional requirements for the target system, however:<br />
# the kernel needs to have the network driver built in, not as a module<br />
# the network init scripts needs to be disabled or patched to avoid collision with nfsroot<br />
<br />
For 1, just change the config file of the target kernel, i.e for<br />
qemux86 on eMenlow, change meta/packages/linux/linux-rp-2.6.29/defconfig-qemux86<br />
to add '''CONFIG_E1000E=y'''.<br />
<br />
''(note: status of initramfs is unknown at the moment)''<br />
<br />
For 2, there are many possible solutions, a relative generic patch can be found here:<br />
<br />
http://git.pokylinux.org/cgit.cgi/poky-contrib/commit/?h=qhe/nfsroot&id=95c6536d33677f177a3aec14f61589702b96cbb7<br />
<br />
Besides, you may also:<br />
* remove /etc/init.d/networking altogether<br />
* remove "auto eth0" in /etc/network/interfaces<br />
<br />
== Setting up after image build ==<br />
<br />
'''''TODO: avoid using sudo'''''<br />
<br />
The following patch provides a script to automatically set up<br />
tftp and nfsroot after image build completes.<br />
<br />
http://git.pokylinux.org/cgit.cgi/poky-contrib/commit/?h=qhe/nfsroot&id=fd51f44f07e1f07d0891082d488a969844bccb2f<br />
<br />
Simply run the<br />
following in the poky build directory, assuming your machine type<br />
is qemux86:<br />
<br />
$ prepare-nfsroot qemux86 -g<br />
<br />
And everything is done. Now just insert the USB stick into the<br />
target machine, power it on, and see if the target image is<br />
booting.<br />
<br />
== External references ==<br />
* [http://etherboot.org/wiki/index.php etherboot.org - The Etherboot/gPXE Wiki]<br />
* [http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob_plain;f=Documentation/filesystems/nfs/nfsroot.txt;hb=HEAD nfsroot reference in kernel/Documentation]<br />
* [http://tldp.org/HOWTO/NFS-Root.html NFS-Root mini-HOWOTO (not maintained)]</div>Scottrif