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Ubuntu Diskless Workstation and X-Terminal Howto – Part 2 – Preparing the diskless image

by on Dec.09, 2010, under Desktop Productivity, Hardware/Disk Management, Networking

Well, after a short break, we are back to our diskless X-Terminal Howto. Today we will cover building the actual diskless image that will be used to boot the X-Terminal. Using ubuntu, the easiest way to do this is to simply install ubuntu on the machine that will be used for the diskless terminal. You can also use a virtual machine to build the image, however this will probably have some interesting issues regarding udev and device detection.

So, basically we be installing ubuntu on the machine itself, and use that install to make an nfs bootable image. So, go ahead and download an ubuntu install cd and have at it. A base install is usually sufficient with working X-Server, network devices etc. You don’t need to install a bunch of applications since those will be served by the server the X-Terminal will attach to. You should make sure you have all the latest updates applied to your install. I also recommend installing the nfs-kernel-server package as well with the command:

apt-get install nfs-kernel-server

Once you have ubuntu installed on your target machine, there are a couple of things we need to do to prepare for making the image NFS bootable.

The first thing we are going to do is modify the initial ram filesystem image to be better suited for network booting. To do this, open a terminal and change to the following directory :

cd /etc/initramfs-tools

We will edit the initramfs.conf file in this directory:

sudo pico initramfs.conf

There are 3 lines in this file that we will want to change. They are shown below:

MODULES=most
BOOT=local
DEVICE=

Change these lines to read:

MODULES=netboot
BOOT=nfs
DEVICE=eth0

Diskless workstations typically require standard wired ethernet connections to work properly. There are some alternatives for wireless, but those are for another article.

After making the changes to this file we will need to regenerate the initial ram disk image for the current kernel. This image will be loaded instead of the standard ubuntu initial ramdisk to allow network booting. Here is the command for creating a new image:

sudo mkinitramfs -o /boot/initrd.img-2.6.35-22-generic.nfs 2.6.35-22-generic

Note the .nfs on the end of the filename (initrd.img-2.6.35-22-generic.nfs) make sure this filename is based on the current kernel version, that can be determined with the command uname -a. The last part of the command is the kernel version to make the initial ramdisk image for.

Here is a sample from a box running ubuntu 10.10:

default@ubuntu-1010:~$ uname -a
Linux ubuntu-1010 2.6.35-22-generic #35-Ubuntu SMP Sat Oct 16 20:36:48 UTC 2010 i686 GNU/Linux
default@ubuntu-1010:~$ sudo mkinitramfs -o /boot/initrd.img-2.6.35-22-generic.nfs 2.6.35-22-generic

The next couple of modifications will have to wait until we have copied the image to the server. So, lets do that next. The best way to copy the image to the server is to mount the servers shared directory that we created in the last article.

The directory was /srv/export/netboot/diskless1. So, lets mount that directory on your workstation. First, lets create a mount point:

sudo mkdir -p /mnt/server

Then we can mount the directory:

sudo mount -t nfs :/srv/netboot/diskless1 /mnt/server

After mounting the directory change to the root of the workstation’s root filesystem and copy the filesystem to the server:

cd /
sudo cp -Rax * /mnt/server

The cp command switches mean copy recursively – ie include all subdirectories (-R) and preserve permissions (a) and limit the copy to one filesystem (x).

After the root file system image is copied from the workstation to the server, we will have to configure the pxelinux command/boot file for the diskless image, as well as move the initrd and kernel image files to the server’s startup_files directory we created in the last article.

First, we will configure the pxelinux command/boot file for the diskless image. This file is a small text file that tells PXE the root file system path, and kernel parameters used for booting the diskless workstation. This file also contains IP autoconfiguration parameters that tell the linux kernel how to configure its network interfaces. Generally, this is handled through dhcp. In ubuntu 10.04 and 10.10 it seemd that in order to boot the diskless reliably, PXE will boot and get the dhcp reservation we created in the first article. Afterwards, the kernel will use hard coded IP address parameters in the kernel command line that match the dhcp reservation the was setup for the workstation. This may not make sense now, but it will soon.

This command/boot file must be saved in a particular location and with a particular name in order for PXE to find it. Essentially, the file needs to be saved in the following directory (if you have been following my server setup examples):

/srv/netboot/startup_files/pxelinux.cfg

The name of the file is the hexadecimal equivalent of the workstations IP address. So, if you used 192.168.0.127 as the IP address reservation on the dhcp server, then the file name will be called:

C0A8007F

This is equivalent to 192(C0).168(A8).0(00).127(7F). You can use the Ubuntu calculator to determine the hex equivalent of your diskless workstations ip.

For our example, the workstation IP will be 192.168.0.127, the IP of the NFS server will be 192.168.0.14, and the path to the diskless root file system will be: /srv/netboot/diskless1.

So, lets look at a sample boot file for the diskless:


DEFAULT /vmlinuz-2.6.35-22-generic
APPEND root=/dev/nfs rw initrd=initrd.img-2.6.35-22-generic.nfs nfsroot=192.168.0.14:/srv/netboot/diskless1 ip=192.168.0.127:192.168.0.14:192.168.0.1:255.255.255.0:::none acpi=force

The first line specifies the kernel image to use. This is tftp’d from the server’s startup_files directory by the diskless workstation at boot. The second line specifies the kernel command line. The root= parameter specifies that the root filesystem will be NFS mounted. The rw means the root filesystem will be read/write. The initrd= parameter specifies the initial ramdisk image we created earlier in this article. The nfsroot parameter specifies the nfs servers path to the root filesystem. The last two parameters, ip= specifies the IP address to use on the LAN interface when the kernel starts. This in the past used to be ip=dhcp. For some reason, in my environment this seems to have stopped working with the latest ubuntu 10.04 kernel and 10.10 kernels. The ip= parameter specifies the IP address of the workstation, the ip of the nfs server, the default gateway, and the network mask, respectively. The :::none are for other unused parameters. Lastly, the acpi=force is for systems where acpi is detected properly. Many older older machines need this parameter to function properly.

Make sure your file includes the right parameter for the ip=, kernel image name, and initrd name. For reference, the kernel image is located in /boot on the workstations image, and the initial ram disk image is what we created earlier in this article.

I will update the article if I can figure out what caused ip=dhcp to stop working properly.

Anyway, we have two more changes to make on the disk image to get a successful boot. The first one is to tell the diskless workstation not to run the normal network configuration. Since our network interface will already be up as part of the PXE process, if the Ubuntu NetworkManager attempts to configure the network stack, we will loose connection to the root filesystem on NFS, causing the kernel init process to fail. So, basically we will tell NetworkManager not to touch the LAN interface by modifying the /etc/network/interfaces file.

If we are using eth0 as our network connection on the diskless terminal, then use the following interfaces file:

auto lo
iface lo inet loopback


iface eth0 inet manual

The last thing we will have to modify is the /etc/fstab file. This file is responsible for telling the Linux kernel which devices to use for the needed file systems on the system. In our case we will simply modify the entry for the root file system.

Normally the entry for the root file system looks something like this:


# / was on /dev/sda1 during installation
UUID=50e370fd-eaf8-486a-adf0-ddb5fe1fb9be /               ext4    errors=remount-ro 0       1

We will change this entry to look like this:


/dev/nfs        /               nfs     defaults    	1       1

This basically tells the kernel that the root file system is nfs mounted.

NOTE: If you intend to leave a hard drive in the diskless workstation, the install of Ubuntu will have set up a swap partition. If you have a machine with low memory, its recommend that you leave the drive in and let Ubuntu detect the swap partition as it boots from the network. If you have 1GB of RAM or more, you will probably be safe removing the hard disk altogether.

The next step is to attempt to boot the diskless workstation from the network. Essentially this usually requires telling the PC’s BIOS to boot from a network device as the first device to attempt.

Usually this is in the BIOS setup. It will vary by PC. Usually this is referred to as Network boot or setting the NIC as the first startup device in your PC’s boot order.

So if you are ready, set your PC to boot from the network, make sure its connected and reboot. If all goes well you will see a screen that looks like this:

If something doesn’t work right, check over your configuration or send me a comment and I try to help. Otherwise your PC should come up into an Ubuntu Desktop logon screen as if it was running from an internal disk drive.

Next article is using the workstation as an X-Terminal for a server (rather than a standalone desktop) and some tuning for performance.

Until next time…

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5 Comments for this entry

  • Casey

    You never explain how to install Ubuntu on diskless machine? Are you supposed to mount the NFS volume before running the installer?

  • Casey

    Nevermind, guess you assume the diskless machine has a disk in it. I think there is a cleaner way. For example you can run the debbootstrap scripts on the NFS machine and do a local install there.

    • admin

      Yes, for my purposes I choose to install ubuntu on the “to be” diskless terminal and copy the filesystem to the server. I have attempted the debbootstrap method a few years back, however I didn’t have any success installing ubuntu-desktop after bringing the basic system up. I should revisit this in a followup article.

  • iconoclast hero

    “sudo cp -Rax * /mnt/server”
    did not preserve permissions… instead i got
    cp: failed to preserve ownership for `/mnt/server/bin/ls’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/lesskey’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/egrep’: Invalid argument
    cp: failed to preserve ownership for /mnt/server/bin/bzegrep: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/bzdiff’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/umount’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/vdir’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/sleep’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/bash’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/bzexe’: Invalid argument
    cp: failed to preserve ownership for `/mnt/server/bin/login’: Invalid argument

    It looks like they’re there but I’m not getting the ownership reserved. I dropped two other tutorials on this because this one looked the best. Hoping not to have to start all over again.

    • admin

      Sorry it took so long to respond – been pretty busy with things other the blogging lately.

      Its possible you don’t have root permissions on the nfs server – make sure that you export your file system with the “no_root_squash” directive.

      Like this:

      /srv/export *(rw,no_root_squash,async,no_subtree_check)

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