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1. Download a ready made rootfs from the Open Build Service.

   We will use openSUSE Tumbleweed on our RPi 3B+:

   • the latest openSUSE-Tumbleweed-ARM-JeOS.aarch64-rootfs tar.xz file

2. Extract the downloaded rootfs

    $ cd /tmp
   
    $ mkdir openSUSE_Tumbleweed
   
    $ xz -d /tmp/openSUSE-Tumbleweed-ARM-JeOS.aarch64-rootfs.aarch64-2020.05.10-Snapshot20200512.tar.xz
   
    $ cd openSUSE_Tumbleweed
   
    $ tar xvf /tmp/openSUSE-Tumbleweed-ARM-JeOS.aarch64-rootfs.aarch64-2020.05.10-Snapshot20200512.tar.xz
   

3. Create a virtual loop back device that will hold the rootfs:

    $ cd /tmp
   
    $ dd if=/dev/zero of=07f32691-opensuse-rootfs.img bs=400M count=10
   
    $ sudo mkfs.ext4 07f32691-opensuse-rootfs.img
   
    $ sudo losetup -fP 07f32691-opensuse-rootfs.img
   

4. Check which loopback devices are allocated by the kernel:

    $ losetup -a
    /dev/loop0: []: (/tmp/07f32691-opensuse-rootfs.img)
   

5. Mount the virtual block device

    $ mkdir 07f32691-rootfs-mount
    
    $ sudo mount -o loop /dev/loop0 07f32691-rootfs-mount
   

6. Copy the content of an existing rootfs image to the mounted block device

    $ cp -R /tmp/downloaded_rootfs/*  07f32691-rootfs-mount/
   

7. Unmount the file and move it to the place where it will be served.

    $ sudo umount 07f32691-rootfs-mount
   
    $ sudo losetup -D
   
    $ sudo mkdir /srv/iscsi
   
    $ sudo mv 07f32691-opensuse-rootfs.img /srv/iscsi
   

8. Prepare the iscsi target and publish it

    $ sudo tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.org.micromec:rpi3-1-opensuse-rootfs
   
    $ sudo tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /srv/iscsi/07f32691-opensuse-rootfs.img
   
    $ sudo tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
   

   Note

   If your iscsi server has other targets then you will need to pick a different tid.

   At this point the rootfs is available on the local network.

9. Save the configuration on the netboot server to remain persistent

    $ sudo tgt-admin --dump | sudo tee  /etc/tgt/conf.d/micromec-cluster.conf
   

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