Diskless / remote boot with Open-iSCSI

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It is possible to start a diskless machine remotely using Open-iSCSI on the client side. You have to take care of these things:

  • create an initrd which will connect the iSCSI node
  • configure your tftp server, so that your machine starts properly via PXE/tftp

This HOWTO explains how to set up your system so that it boots a diskless station using PXE/tftp and Open-iSCSI.

Creating initrd

Below some theory; for practical examples, see downloads section.

Your initrd has to do the following things:

  • load all needed modules, like:
    • network card modules (e1000, tg3, mii, 8139too, e100, depending on the card you use etc.)
    • filesystem modules (jbd, ext3, depending on the filesystem you use)
    • SCSI modules (scsi_mod, sd_mod)
    • Open-iSCSI modules (scsi_transport_iscsi, libiscsi, iscsi_tcp)
  • mount /proc and /sys
  • bring a network interface up
  • initiate a iSCSI session with iscsistart
  • mount your filesystem
  • switch to a new root
  • execute /sbin/init from a new root

Preparing initrd

Note that the below instruction use common tools from your favourite distribution. You may create a similar initrd with busybox/uClibc.

  • create a directory for your Open-ISCSI-aware initrd:
mkdir initrd
  • create all needed directories:
cd initrd
mkdir -p bin dev etc lib/modules proc sys sysroot
ln -s bin sbin
  • copy the following binaries to bin/:
bash  cat  chroot  echo  ifconfig  insmod  iscsistart  mount  sleep

You can do it with a following command:

which bash cat chroot echo ifconfig insmod iscsistart mount sleep | xargs -i{} cp {} bin/

If your distribution doesn't ship iscsistart (most distros don't), you have to compile open-iscsi yourself - you'll find there iscsistart.

  • copy shared libraries to lib/; you will find the shared libraries with ldd tool, for example:
# ldd bash
       linux-gate.so.1 =>  (0xb7fa6000)
       libtermcap.so.2 => /lib/libtermcap.so.2 (0xb7f9d000)
       libdl.so.2 => /lib/libdl.so.2 (0xb7f99000)
       libc.so.6 => /lib/i686/libc.so.6 (0xb7e6a000)
       /lib/ld-linux.so.2 (0xb7fa7000)

  • after all binaries and libraries are copied to correct places, verify if you didn't forget anything with chroot command - you may get a similar "no name" prompt (it's OK, since there are no users in that initrd), and all binaries should be able to start:
# cd initrd
# chroot .
[I have no name!@localhost /]# mount --help     
  • create needed nodes in dev/ (with mknod tool, or just copy them from your /dev):
console  sda  sda1  sda2

  • create the init file (don't forget to chmod 755 init); place it in the root of your initrd directory; note we load some modules here - you have to copy the modules to /lib/modules/ in your initrd; here's the example init file which detects kernel command line parameters like initiator name, target IP etc.:

# Load modules
# You may only need to load the network card modules you will use
# To find module dependencies, you can use "modinfo" tool

echo "Loading jbd.ko module"
insmod /lib/modules/jbd.ko
# On some kernels, you will need mbcache module if it is not in the kernel
echo "Loading mbcache.ko module"
insmod /lib/modules/mbcache.ko
echo "Loading ext3.ko module"
insmod /lib/modules/ext3.ko

echo "Loading libcrc32c.ko module"
insmod /lib/modules/libcrc32c.ko
echo "Loading crc32c.ko module"
insmod /lib/modules/crc32c.ko

# Network card modules - start
echo "Loading mii.ko module"
insmod /lib/modules/mii.ko
echo "Loading 8139too.ko module"
insmod /lib/modules/8139too.ko

echo "Loading e100.ko module"
insmod /lib/modules/e100.ko

echo "Loading e1000.ko module"
insmod /lib/modules/e1000.ko

echo "Loading tulip.ko module"
insmod /lib/modules/tulip.ko

echo "Loading tg3.ko module"
insmod /lib/modules/tg3.ko
# Network card modules - end

echo "Loading scsi_mod.ko module"
insmod /lib/modules/scsi_mod.ko
echo "Loading sd_mod.ko module"
insmod /lib/modules/sd_mod.ko

echo "Loading scsi_transport_iscsi.ko module"
insmod /lib/modules/scsi_transport_iscsi.ko
echo "Loading libiscsi.ko module"
insmod /lib/modules/libiscsi.ko
echo "Loading iscsi_tcp.ko module"
insmod /lib/modules/iscsi_tcp.ko

# Mount /proc and /sys
echo Mounting /proc filesystem
mount -t proc /proc /proc

echo Mounting sysfs
mount -t sysfs /sys /sys

# We need to extract four command line parameters form /proc/cmdline:
# iscsi_i_ip - local initiator IP address/netmask (i.e.
# iscsi_i    - local initiator name (InitiatorName)
# iscsi_t    - remote target name (TargetName)
# iscsi_a    - iSCSI target IP address

# Read the kernel cmdline
CMDLINE=$(cat /proc/cmdline)

# Find out IP/NETMASK first

# Find InitiatorName

# Find TargetName

# Find iSCSI target IP address

# Bring the network interface up
ifconfig eth0 ${ISCSI_I_IP%/*} netmask ${ISCSI_I_IP#*/}

# Connect the iSCSI drive
iscsistart -i "$ISCSI_I" -t "$ISCSI_T" -g 1 -a $ISCSI_A

mount -o ro /dev/sda2 /sysroot

echo Switching to new root
cd /sysroot

# Uncomment "bash" below, and comment out "exec ..." if you are having booting problems.
# It will give you a bash shell with limited tools.
exec chroot . sh -c 'exec /sbin/init'

Creating initrd with cpio

Now that you have all the files ready, create initrd image:

find ./ | cpio -H newc -o > ../initrd.cpio
cd ..
gzip -9 initrd.cpio
mv initrd.cpio.gz initrd.img

Next, copy initrd.img to your tftp server.

Configuring tftp server

Add something like that to a pxelinux.cfg/default file to initiate a remote boot by hand (not recommended):

LABEL remote1
   KERNEL remote/vmlinuz-2.6.17-5mdv
   APPEND initrd=remote/initrd.img iscsi_i=iqn.2007-01.com.example:server.remote1 iscsi_i_ip= iscsi_t=iqn.2007-01.com.example:storage.remote1 iscsi_a=

You have to add these parameters to APPEND line appropriately:

  • initrd - initrd image, for example, initrd=remote/initrd.img
  • iscsi_i_ip - local initiator IP address/netmask (i.e., for example, iscsi_i_ip=
  • iscsi_i - local initiator name (InitiatorName), for example, iscsi_i=iqn.2007-01.com.example:server.remote1
  • iscsi_t - remote target name (TargetName), for example, iscsi_t=iqn.2007-01.com.example:storage.remote1
  • iscsi_a - iSCSI target IP address, for example, iscsi_a=

It is recommended that you add the above entry to a pxelinux.cfg/aa-bb-cc-dd-ee-ff file; aa-bb-cc-dd-ee-ff being the MAC address of the PC you want to boot remotely with Open-iSCSI / PXE.


Go to downloads page.

Additional info / troubleshooting

See diskless iSCSI troubleshooting page.


For general Open-iSCSI info, please ask at open-iscsi mailing list.

Keywords: Open-iSCSI remote boot, diskless, iSCSI, Xen, tftp, PXE, network boot