Netbooting ARM/MIPS devices: server setup

I was asked to share details about my root-over-NFS setup so here they are. I decided to split how-to in two posts: server/kernel part and u-boot part.

Usual components in the setup are:

• DHCP server
• TFTP server
• NFS server
• NAT (optional)

DHCP server

I use net/isc-dhcp42-server as a server. Sample dhcpd.conf:

option root-opts code 130 = string; # NFS / mount options
log-facility local7;

subnet 192.168.10.0 netmask 255.255.255.0 {
        server-name "cinderella.bluezbox.com";
        server-identifier 192.168.10.1;
        option subnet-mask 255.255.255.0;
        option broadcast-address 192.168.10.255;
        option domain-name-servers 8.8.8.8;
        option domain-name "bluezbox.com";
        next-server 192.168.10.1;
        option routers 192.168.10.1;
}

group {
        host pandaboard {
                hardware ethernet 0E:60:33:B1:46:01;
                fixed-address 192.168.10.90;
                filename "kernel.PANDA.bin";
                option root-path "/src/FreeBSD/nfs/armv6";
                option root-opts "nolockd";
        }

        host rpi {
                hardware ethernet b8:27:eb:f6:08:83;
                fixed-address 192.168.10.91;
                filename "ubldr";
                option root-path "/src/FreeBSD/nfs/rpi";
                option root-opts "nolockd";
        }
}

Config is pretty self-explanatory. I use google’s 8.8.8.8 nameserver but you can change it to your very own DNS server. Difference between various filename “…” will be explained later.

dhcpd should be enabled in rc.conf(5)

dhcpd_enable="YES"

TFTP server

TFTP server provides access to all files described in filename “…” options so it’s better to keep them together. By default it’s /tftpboot directory but I have whole drive dedicated to FreeBSD development environment and mounted under /src/FreeBSD mountpoint. So I keep everything there and my TFTP server root is /src/FreeBSD/tftpboot. TFTP server is standard FreeBSD’s one and config line in inetd.conf(8) looks like:

tftp    dgram   udp     wait    root    /usr/libexec/tftpd      tftpd -l -s /src/FreeBSD/tftpboot

inted should be enabled in rc.conf(5)

inetd_enable="YES"

NFS Server

NFS server is not just one daemon but several services combined. So rc.conf(5) part of config looks like this:

rpcbind_enable="YES"
rpc_statd_enable="YES"
rpc_lockd_enable="YES"
nfs_server_enable="YES"
mountd_enable="YES"

Filesystems that are exported via NFS listed in exports(5). Mine contains following:

# Mind mount points obj and nfs are different
/usr/ports -maproot=0 -network 192.168.10.0/16
/src/FreeBSD/head /src/FreeBSD/nfs/rpi /src/FreeBSD/nfs/armv6 /src/FreeBSD/nfs/am335x -maproot=0 -network 192.168.10.0/16

Note that you can join several directories into one line only if they belong to the same mount point.

NAT

If you’re planning on building ports on the device – you’ll need internet access on it. All my devices are restricted to one LAN with laptop acting as a gateway. I use pf(4) for NATing. Config:
/etc/pf.conf(5)

ext_if=em0
rede="{192.168.0.0/16}"

nat on $ext_if from $rede to any -> ($ext_if)

and rc.conf(5)

gateway_enable="YES"

pf_enable="YES"
pf_rules="/etc/pf.conf"
pf_flags=""

Kernel config

FreeBSD kernel should be properly configured in order to be suitable for mounting root over NFS:

options         NFSCL
options         NFSCLIENT # NFS v3
options         NFS_ROOT
options         BOOTP_NFSROOT
options         BOOTP_COMPAT
options         BOOTP
options         BOOTP_NFSV3
options         BOOTP_WIRED_TO=ue0

BOOTP_WIRED_TO value is SoC-specific. If you do not have full control over your DHCP server (e.g. it’s cable modem) and can’t specify root-path/root-opts you still can hardcode root location by removing BOOTP_NFSROOT and adding

options         ROOTDEVNAME=\"nfs:192.168.10:/src/FreeBSD/nfs/rpi\"

Installation

Depending on your boot sequence installation consists of one or two steps.

Normal system installation, e.g.:

sudo -E make TARGET_ARCH=armv6 DESTDIR=/src/FreeBSD/nfs/rpi -DDB_FROM_SRC installworld
sudo -E make TARGET_ARCH=armv6 DESTDIR=/src/FreeBSD/nfs/rpi -DDB_FROM_SRC distribution

And installing kernel copying kernel to tftpboot directory:

sudo -E make TARGET_ARCH=armv6 DESTDIR=/src/FreeBSD/nfs/rpi -DDB_FROM_SRC installkernel
cp /src/FreeBSD/nfs/rpi/boot/kernel/kernel /src/FreeBSD/tftpboot/kernel.RPI 

In some cases you’d want to use kernel.bin instead of kernel (more on it in next post) so second step would look like

sudo -E make TARGET_ARCH=armv6 DESTDIR=/src/FreeBSD/nfs/rpi -DDB_FROM_SRC KERNEL_EXTRA_INSTALL=kernel.bin installkernel
cp /src/FreeBSD/nfs/rpi/boot/kernel/kernel.bin /src/FreeBSD/tftpboot/kernel.RPI.bin

And if you’re going to use ubldr, there is no need to copy installed kernel anywhere.

More details on different types of binaries and boot process in the next post