UbuntuHelp:DisklessUbuntuHowto
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目录
What is diskless booting?
Diskless booting is using a remote system or systems to store the kernel and the filesystem that will be used on other computer(s).
Why do it?
Imagine my case I admin about 25 public workstations for a local library, if they want something changed across the board I can either go sit at each PC and spend X minutes on it, adding up to who knows how many hours, or I can simply make the change at any one of the 25 systems and have it effect every system equally. The same goes for updates and many other operations. It really eases support issues.
How is this different than ThinClientHowto?
Thin clients use some of the same principals but they also connect to a remote X session, which means everything runs on the remote server, all applications will consume the servers resources, such as RAM and CPU cycles. Diskless Booting simply uses the remote server for storage and still runs all applications on the local client station. This works better if you have full powered PC's to work with, and are working with a large number of clients that would require too much CPU and RAM to run all their applications on one server. It is different enough to have multiple machines mounting the same root filesystem as opposed to simply being a remote monitor and keyboard to warrant a separate how-to I think. Oliver Grawert says :- you could have achieved this easier by following the thin client howto, remove the ltsp-client package from the chroot and install ubuntu-desktop (or whatever desktop you want) there, would save you a lot of configuration work ;)
How does it work?
There are a lot of parallels to ThinClientHowto, diskless booting requires a DHCP server which a bootable PXE network card will query to get its configuration and location of the file to tftp from the server, after booting the PXE image the client will tftp and boot the kernel image(with args specified in the pxe config), those args will tell the kernel how to configure itself, and the path to mount the NFS share where it's / directory is located.
Requirements
- An Ubuntu system with (preferably) nfs-kernel-server and tftpd server (the server)
- At least one PXE-bootable system (the client)
- It helps to have the client set up in its final configuration before you start
- Enough disk space on the server to hold the client filesystem
- A fast network connection between the client and the server
- A DHCP server which is capable of supporting PXE clients, or a separate network segment where you can run a dedicated DHCP server
- A good understanding of Linux
Getting Started
Naming Conventions
Client: A diskless system that you wish to boot via a network connection
<
>Server: An always-on system which will provide the neccesary files to allow the client to boot over the network
Set up your Server
- Install the required packages
sudo apt-get install dhcp3-server tftpd-hpa syslinux nfs-kernel-server initramfs-tools
- Configure your DHCP server
<
>You need to set up the DHCP server to offer /tftpboot/pxelinux.0 as a boot file as a minimum. You also assign a fixed IP to the machine you want to boot with PXE (the client). A range of other options are also available but are beyond the scope of this article. Your dhcpd.conf might look like this assuming your subnet is 192.168.2.0
allow booting;
allow bootp;
subnet 192.168.2.0 netmask 255.255.255.0 {
range 192.168.2.xxx 192.168.2.xxx;
option broadcast-address 192.168.2.255;
option routers 192.168.2.xxx;
option domain-name-servers 192.168.2.xxx;
filename "/pxelinux.0";
}
# force the client to this ip for pxe.
# This is only necessary assuming you want to send different images to different computers.
host pxe_client {
hardware ethernet xx:xx:xx:xx:xx:xx;
fixed-address 192.168.2.xxx;
}
NOTE 1: You will need to replace the 'xx:xx:xx:xx:xx:xx' and the '192.168.2.xxx' with your own values
<
>NOTE 2: the filename is a relative path to the root of the tftp server.
- Configure the TFTP Server
<
>We need to set tftp-hpa to run in daemon mode and to use /tftpboot as its root directory.
<
>Here is an example /etc/default/tftpd-hpa file
#Defaults for tftpd-hpa RUN_DAEMON="yes" OPTIONS="-l -s /tftpboot"
- Configure your tftp root directory
- Create directories
sudo mkdir -p /tftpboot/pxelinux.cfg
- Copy across bootfile
sudo cp /usr/lib/syslinux/pxelinux.0 /tftpboot
- Create default configuration file /tftpboot/pxelinux.cfg/default
LABEL linux KERNEL vmlinuz-2.6.15-23-686 APPEND root=/dev/nfs initrd=initrd.img-2.6.15-23-686 nfsroot=192.168.2.2:/nfsroot ip=dhcp rw
NOTE1: your nfs server IP address, kernel name, and initrd name will likely be different. If you have a preconfigured system the names should be the names of the kernel and initrd (see below) on the client system <
>NOTE2: to find the vmlinuz typeuname -r<
>NOTE3: There are more options available such as MAC or IP identification for multiple config files see syslinux/pxelinux documentation for help.- Set permissions
sudo chmod -R 777 /tftpboot
NOTE:If the files do not have the correct permissions you will receive a "File Not Found" or "Permission Denied" error.
- Start the tftp-hpa service:
sudo /etc/init.d/tftp-hpa start
- Configure OS root
- Create a directory to hold the OS files for the client
sudo mkdir /nfsroot
- configure your /etc/exports to export your /nfsroot
/nfsroot 192.168.2.xxx(rw,no_root_squash,async)
NOTE: The '192.168.2.xxx' should be replaced with either the client IP or hostname for single installations, or wildcards to match the set of servers you are using.
- sync your exports
sudo exportfs -rv
Creating your NFS installation
There are a few ways you can go about this:
- debbootstrap (as outlined at Installation/OnNFSDrive)
- copying the install from your server
- install [xk]ubuntu on the client from CD, after you've got your system installed and working on the network mount the /nfsroot and copy everything from your working system to it.
This tutorial will focus on the last option. The commands in this section should be carried out on the client machine unless it is explicitly noted otherwise. You should ensure that the following package is installed on the client
nfs-common- Copy current kernel version to your home directory.
<
>uname -r will print your kernel version, and ~ is shorthand for your home directory.cp /boot/vmlinuz-`uname -r` ~
- Create an initrd.img file
- Change the BOOT flag to nfs in /etc/initramfs-tools/initramfs.conf
# # BOOT: [ local | nfs ] # # local - Boot off of local media (harddrive, USB stick). # # nfs - Boot using an NFS drive as the root of the drive. # BOOT=nfs
- Change the MODULES flag to netboot in /etc/initramfs-tools/initramfs.conf
# # MODULES: [ most | netboot | dep | list ] # # most - Add all framebuffer, acpi, filesystem, and harddrive drivers. # # dep - Try and guess which modules to load. # # netboot - Add the base modules, network modules, but skip block devices. # # list - Only include modules from the 'additional modules' list # MODULES=netboot
NOTE: if you have anything in /etc/initramfs-tools/conf.d/driver-policy, this line will be ignored.
- Run mkinitramfs
<
>Some people prefer to append the kernel version to the end of the initrd.img file just to keep track of things. Since we just found which version our kernel is, run the commandmkinitramfs -o /home/<USERNAME>/initrd.img-2.6.20-16-generic
NOTE: you can also accomplish the same result as above with:
update-initramfs -c -k 2.6.20-16-generic -b /home/<USERNAME>
but this has the advantage of choosing the kernel version specified instead of using the most recent installed
- Copy OS files to the server
mount -tnfs -onolock 192.168.1.2:/nfsroot /mnt cp -ax /. /mnt/. cp -ax /dev/. /mnt/dev/.
NOTE: If the client source installation you copied the files from should remain bootable and usable from local hard disk, restore the former BOOT=local and MODULES=most options you changed in /etc/initramfs-tools/initramfs.conf. Otherwise, the first time you update the kernel image on the originating installation, the initram will be built for network boot, giving you "can't open /tmp/net-eth0.conf" and "kernel panic". Skip this step if you no longer need the source client installation.
- Copy kernel and initrd to tftp root.
<
>Run these commands ON THE SERVERcp /nfsroot/home/<USERNAME>/<vmlinuz-xxxx> /tftpboot/ cp /nfsroot/home/<USERNAME>/<initrd.img-xxxx> /tftpboot/
- Modify /nfsroot/etc/network/interfaces
<
>When booting over the network, the client will already have carried out a DHCP discovery before the OS is reached. For this reason you should ensure the OS does not try to reconfigure the interface later. <
>You should set your network interface to be "manual" not "auto" or "dhcp". Below is an example file.# This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # The primary network interface, commented out for NFS root #auto eth0 #iface eth0 inet dhcp iface eth0 inet manual
NOTE: For Ubuntu 7.04 (Feisty Fawn) it seems the /etc/network/interfaces needs a little tweak, in order *not* to have the NetworkManager fiddle with the interface since it's already configured (see also bug #111227 : "NFS-root support indirectly broken in Feisty")
- Configure fstab
<
>/nfsroot/etc/fstab contains the information the client will use to mount file systems on boot, edit it to ensure it looks something like this ('note no swap')# /etc/fstab: static file system information. # # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc defaults 0 0 /dev/nfs / nfs defaults 1 1 none /tmp tmpfs defaults 0 0 none /var/run tmpfs defaults 0 0 none /var/lock tmpfs defaults 0 0 none /var/tmp tmpfs defaults 0 0 /dev/hdc /media/cdrom0 udf,iso9660 user,noauto 0 0
NOTE: if you have entries for other tmpfs that's fine to leave them in there
Alternative to the above method
An alternative to parts 1, 2, 3 and 4 exists, if you are copying your nfsroot to the same server as your tftp server. To use the alternative, do not copy your vmlinux-2.#.#-#-generic file to your home directory. Do part 2(a) and then do
sudo mkinitramfs -o /boot/initrd.img-Xwhere of course X is your kernel version ('2.6.20-16-generic' from the mkinitramfs example shown above). Do part 3. On The Server Instead of copying your kernel and initrd into the tftp folder as suggested in part 4, cd into the boot folder in the root of the machine that your just copied over in part 3. If you followed part 3 exactly, this will be in /nfsroot/boot/. Create a symlink called 'vmlinuz' what points to your current kernel version in that same directory. Create another symlink called 'initrd.img' that points to the initrd.img that your are currently using (same version as your kernel). Create one more symlink called 'config' that points to the config your using. You will likely need to create these symlinks with sudo. They will help keep your tftp configuration simple and can help ease system upgrades, all you have to do is upgrade the 'vmlinuz', 'initrd.img', and 'config' symlinks to point to the new files. cd into your tftp directory, and create symlinks to the 'vmlinuz', 'initrd.img', and 'config' symlinks you just created. If you will be doing this for more than one machine, you may want to add the name of the machine to the symlink in this directory so that you can tell them apart. From here, continue at part 5 of the above instructions. When you finish the from part 5 onward of the above instructions you should have a booting machine in the same state as you would had you followed them from part 1 onwards.Setup your client
Enter your BIOS settings and configure your system to boot from LAN If you have options for different LAN boot methods choose PXE
Now What?
Reboot your client PC it should get it's net config from the DHCP server, download the pxelinux image, download and boot the kernel, mount your root fs and continue to boot just as if it were using its internal HD, only now you can yank that HD out and use it for something else, that machine doesn't need it any more :)
Adding a swap file
In case you do need or want to set up a swapfile, here's what I did to get one working:
sudo apt-get install dphys-swapfile
this package sets up a swap file at /var/swap that is 2x your current ram. however, it still doesn't setup the swapfile on its own, though it does try. to get the swap file working the rest of the way, do:
sudo losetup /dev/loop0 /var/swap sudo swapon /dev/loop0
then, run top and you will see you have a swap file. however, put in as much ram as you need for what you are going to run, and just look at your swap file as "in case of emergency", because it is not efficient as a ram or a regular swap file, but should keep something from crashing. I'm running mythtv on top of a full feisty desktop, and tried it with 256mb ram, and myth-frontend would crash when i would try to bring it up. with the swap file, it would launch, but would take a while. i added an additional 256mb to bring the total to 512mb and it runs flawless, and i add the swap file just in case. i just make a script for it to set up the swap file at boot.
Static IP
As described in #175324 ipconfig have problems with DHCP relays. Static IP is configured by parameter:
ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
<client-ip> IP address of the client. If empty, the address will either be determined by RARP/BOOTP/DHCP. What protocol is used de- pends on the <autoconf> parameter. If this parameter is not empty, autoconf will be used. <server-ip> IP address of the NFS server. If RARP is used to determine the client address and this parameter is NOT empty only replies from the specified server are accepted. To use different RARP and NFS server, specify your RARP server here (or leave it blank), and specify your NFS server in the `nfsroot' parameter (see above). If this entry is blank the address of the server is used which answered the RARP/BOOTP/DHCP request. <gw-ip> IP address of a gateway if the server is on a different subnet. If this entry is empty no gateway is used and the server is assumed to be on the local network, unless a value has been received by BOOTP/DHCP. <netmask> Netmask for local network interface. If this is empty, the netmask is derived from the client IP address assuming classful addressing, unless overridden in BOOTP/DHCP reply. <hostname> Name of the client. If empty, the client IP address is used in ASCII notation, or the value received by BOOTP/DHCP. <device> Name of network device to use. If this is empty, all devices are used for RARP/BOOTP/DHCP requests, and the first one we receive a reply on is configured. If you have only one device, you can safely leave this blank. <autoconf> Method to use for autoconfiguration. If this is either 'rarp', 'bootp', or 'dhcp' the specified protocol is used. If the value is 'both', 'all' or empty, all protocols are used. 'off', 'static' or 'none' means no autoconfiguration.
Gotchas
- Remember to use -o nolock when first mounting your NFS or have portmapper running or you'll end up with a long (nearly 2 min) hang mounting the remote NFS.
- If you are going to have multiple systems share this root you need to make sure some directories like /var/run, /var/lock and /tmp are mounted in tmpfs so different systems won't be conflicting into each other.
- You probably also want to mount /media in tmpfs space if you don't want every workstation having access to every other workstations storage media.
- Think of things in cron like slocate - do you really want 25 computers trying to updatedb at 4AM all on the same HD?
- Don't forget graphics drivers, conflicts can arise if your machines use varying graphics cards.
- Do you really want all of the machines trying to append to the same log file? Maybe have each machine send their logs to a central log server, or mount the log directories over NFS.
- With this setup under 8.10 to get any NFS directories to mount in the fstab on boot, you need to add ASYNCMOUNTNFS=no to /etc/default/rcS (because otherwise /etc/init.d/mountnfs.sh expects /etc/network/ifup.d/ scripts to take care of it (which don't run for manual interfaces))
- If you intend to use AutoFS to automatically mount/unmount directories on a diskless system, you may run into this small bump in the road. There is a one-liner fix in the autofs init.d script to get you going again.
- Beware of poorly programed applications which crash hard with errors indicating there is already another instance of itself running if you ever have a hard crash and have to use the reboot/power button. Many applications, including Firefox, Thunderbird, Skype and many others don't handle such crashes cleanly and will give you such errors if you ever find yourself in this situation. To remedy it, you must _manually_ go through their config folders (for example, firefox uses ~/.mozilla/firefox/XXX.default/.) and delete all of the locks. For Firefox and related browsers, you may also have to delete several of the .sqlite files in order to get your history, in-browser search bar and such features to work properly again; as for which ones, you'll have to use trial and error to figure it out (or, rm -rf *.sqlite does it too, but assures you obliterate everything at the same time). Also while your looking for locks to remove in the respective config folders, look for and delete files such as .nfs00000000e000e47e0000000a ; These were left by the crashed instance of the application and do not directly get in your way but its cruft you don't want sitting around.
Credits
For the feisty interfaces fix and locating your current kernel: http://developer.novell.com/wiki/index.php/HOWTO:_Convert_Ubuntu_to_Diskless For the tftp-hpa config - dodox in the forums: http://ubuntuforums.org/showthread.php?t=236518
