Some infos in debian-wiki: https://www.debian.org/releases/stretch/armhf/ch05s01.html.en

# Enable the TFTP server
enable-tftp
tftp-root=/var/lib/tftp

mkdir /var/lib/tftp


systemctl enable dnsmasq.service
systemctl start dnsmasq.service

or

service dnsmasq restart

• https://rechtzeit.wordpress.com/2013/01/16/tftp-boot-using-u-boot/

setenv ipaddr 192.168.0.11
setenv netmask 255.255.255.0
setenv serverip 192.168.0.10
setenv bootfile uImage
setenv bootargs console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootwait ip=dhcp

tftp 0x80200000 ${bootfile}
bootm 0x80200000

uenv.txt (using my uboot + reload bootmenu):

ipaddr=192.168.0.11
netmask=255.255.255.0
serverip=192.168.0.10

bootfile=uImage
netbootargs=console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootwait ip=dhcp

bootmenu_1=2. Boot kernel from TFTP.=run bootnet
bootnet=printenv; setenv bootargs ${netbootargs};tftp 0x80200000 ${bootfile};bootm

this replaces bootmenu-entry #2 with tftp-boot and loads bootfile from tftp-server (serverip)…this part works so far with dnsmasq-tftp

needs strings-command (currently untested)

tftp ${loadaddr} 192.168.0.10:files.lst
strings ${loadaddr} ${filesize}

Currently untested

Initrd-steps on ibm: https://www.ibm.com/developerworks/library/l-initrd/

to use a initramfs add this option (change filename) to your .config (tested with bitmasters initramfs)

CONFIG_INITRAMFS_SOURCE="../initramfs.cpio"

add this to your netbootargs:

ip=192.168.0.11:192.168.0.10:192.168.0.10:255.255.255.0::wan

documentation says

ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns0-ip>:<dns1-ip>:<ntp0-ip>

• https://lauri.võsandi.com/2014/08/cubietruck-over-nfs.html
• https://gmelikov.com/2018/02/25/debian-stretch-diskless-pxe-boot/

debootstrap needs exec and dev-options on target-partition, add these to fstab and run “mount -o remount mountpoint”

targetdir=bpi-r2-nfs-root

sudo apt-get install debootstrap qemu-user-static binfmt-support

sudo debootstrap --foreign --arch=armhf stretch $targetdir
sudo cp /usr/bin/qemu*-arm-static $targetdir/usr/bin/
sudo chroot $targetdir /debootstrap/debootstrap --second-stage

sudo mkdir -p $targetdir/dev/pts
sudo mount --bind /dev/pts $targetdir/dev/pts
sudo mount --bind /proc $targetdir/proc/
#sudo mount --bind /home $targetdir/home/

sudo chroot $targetdir

ln -s /proc/self/mounts /etc/mtab

nano /etc/fstab

proc /proc proc defaults 0 0
/dev/nfs / nfs nolock 0 0
none /tmp tmpfs defaults 0 0
none /var/tmp tmpfs defaults 0 0
none /var/lib/lightdm tmpfs defaults 0 0
none /media tmpfs defaults 0 0
none /var/log tmpfs defaults 0 0
#192.168.81.1:/home /home nfs nolock 1 2

nano /etc/apt/sources.list

deb http://deb.debian.org/debian stretch main
deb-src http://deb.debian.org/debian stretch main

deb http://security.debian.org stretch/updates main
deb-src http://security.debian.org stretch/updates main


nano /etc/resolv.conf
nameserver 192.168.0.10

#change root-passwort, without it you cannot login!
passwd

#change hostname
nano /etc/hostname
#add hostname also to loopback-device (127.0.0.1 + ::1)
nano /etc/hosts

apt-get update

#change network-config if you don't want to set it via uboot or dhcp
nano /etc/network/interfaces

NFS-Server-install:

sudo apt-get install nfs-kernel-server
#status
sudo service nfs-kernel-server status
#create root-folder
mkdir -p /var/nfs/bpi-r2
#add this folder to exports-file
echo "/var/nfs/bpi-r2 192.168.0.0/24(rw,sync,no_root_squash)">>/etc/exports
#unpack the debootstrapped rootfs to it

test on client

apt install nfs-common
mkdir /mnt/nfs
mount -t nfs 192.168.0.10:/var/nfs/bpi-r2 /mnt/nfs

with fstab

#entry in /etc/fstab:
192.168.0.10:/var/nfs/bpi-r2 /media/nfs nfs rw 0 0

#create target-dir and mount it
sudo mkdir /media/nfs
sudo mount /media/nfs

Uboot:

#netboot                                                                                                                                                                                           
ipaddr=192.168.0.11                                                                                                                                                                                
netmask=255.255.255.0                                                                                                                                                                              
serverip=192.168.0.10                                                                                                                                                                              
bootfile=uImage_4.14.73                                                                                                                                                                            
                                                                                                                                                                                                   
set_netargs=setenv netargs "console=ttyS0,115200 root=/dev/mmcblk0p2 rw rootwait ip=${ipaddr}:${serverip}:${serverip}:${netmask}::wan::${serverip}:8.8.8.8"                                        
                                                                                                                                                                                                   
nfs_ip=192.168.0.10                                                                                                                                                                                
nfs_rfs=/var/nfs/bpi-r2                                                                                                                                                                            
                                                                                                                                                                                                   
#netargs=console=ttyS0,115200 ip=192.168.0.11:192.168.0.10:192.168.0.10:255.255.255.0::wan::192.168.0.10:8.8.8.8 root=/dev/nfs rw nfsroot=192.168.0.10:/var/nfs/bpi-r2,nfsvers=3,tcp nfsrootdebug  
                                                                                                                                                                                                   
set_nfsargs=setenv nfsargs "root=/dev/nfs rw nfsroot=${nfs_ip}:${nfs_rfs},nfsvers=3,tcp nfsrootdebug"                                                                                              
                                                                                                                                                                                                   
#new bootmenuentries (start at bootmenu_6) require reload bootmenu because uenv.txt is not loaded before display menu                                                                              
bootnet=run set_netargs;run set_nfsargs; setenv bootargs "${netargs} ${nfsargs}"; printenv; tftp 0x80200000 ${bootfile};bootm
bootmenu_1=2. Boot kernel from TFTP.=run bootnet

• https://wiki.dave.eu/index.php/Setting_up_tftp_and_nfs
• https://elinux.org/TFTP_Boot_and_NFS_Root_Filesystems
• https://community.nxp.com/docs/DOC-95051
• https://systemausfall.org/wikis/howto/FAI (de)