Diskless nodes/fr

This HOWTO will help with creating and setting up diskless nodes with Gentoo Linux.

À propos de ce guide
This HOWTO will help setting up diskless workstations based on the Gentoo Linux distribution. This is guide is intended to make the process as user friendly as possible and cater to the Linux newbie, because everyone was at a certain point :) While an experienced user could easily tie the multiple HOWTOs available on diskless nodes and networking together it's hoped that this guide can ease the installation for all interested users, geeks or not.

Qu'est-ce qu'une machine sans disque ?
A diskless machine is a PC without any of the usual boot devices such as hard disks, floppy drives or CD-ROMs. The diskless node boots off the network and needs a server that will provide it with storage space as a local hard disk would. From now on the server will be the master, while the diskless machine gets called the slave (what's in a name :). The slave node needs a network adapter that supports PXE booting or Etherboot; check Etherboot.org for support listings. Most modern cards support PXE and many built-in adapters on motherboards will also work.

Before starting
Gentoo should be installed on the master node and enough space on the master to store the file systems of the slave nodes that are going to be hosted. Also make sure there is one interface to the internet separated from the local area connection.

À propos des noyaux
The kernel is the software that sits between the hardware and all other software that is loaded on the machine, essentially the heart of a kernel based operating system. When a computer is started, the BIOS executes the instructions found at the reserved boot space of the hard drive. These instructions are typically a boot loader that loads a kernel. After a kernel has been loaded all processes are handled by the kernel.

For more information on kernels and kernel configuration check out the kernel article.

Configurer le noyau du maître
The master kernel can be as large and as customized as desired but there are a few required kernel options that need to be selected. Go into the kernel configuration menu by typing:

There should be a grey and blue GUI that offers a safe alternative to manually editing the file. If the kernel is currently functioning well it might be a good idea to save the current configuration file by exiting the GUI and typing:

Go into the following sub-menus and make sure the listed items are checked as built-in (and NOT as modular). The options show below are taken from the 2.6.10 kernel version. If a different version is used, the text or sequence might differ. Just make sure to select at least those shown below.

If access to internet through the master node is required and/or a secure firewall is needed make sure to add support for iptables:

If packet filtering is required, add the rest as modules later. Make sure to read the Gentoo Security Handbook Chapter about Firewalls on how to set this up properly.

After the master kernel has been re-configured, it needs to be rebuilt:

Then add an entry for that new kernel into or  depending on which bootloader that is being used and make the new kernel the default one. Now that the new bzImage has been copied into the boot directory all that has to be done is to reboot the system in order to load these new options.

À propos du noyau de l'esclave
It is recommended that the slave kernel be compiled without any modules, since loading and setting them up via remote boot is a difficult and unnecessary process. Additionally, the slave kernel should be as small and compact as possible in order to efficiently boot from the network. The slave's kernel is going to be compiled in the same place where the master was configured.

Pour éviter toute confusion et toute perte de temps, il vaut mieux garder une copie de la configuration du noyau maître comme ceci :

The slave's kernel is now to be configured in the same fashion as the master's kernel. If a fresh configuration file is needed it can be recovered from the default file by typing:

Ensuite, utilisez l'interface de configuration en tapant :

Make sure to select the following options as built-in and NOT as kernel modules:

Now the slave's kernel needs to be compiled. Be careful here not to overwrite or mess up the modules (if any) that have been built for the master:

Now create the directory on the master that will be used to hold slaves' files and required system files. The is used but any location preferred may be chosen here. Now copy the slave's bzImage into the directory:

Configurer un système de fichiers préliminaire pour l'esclave
The master and slave filesystems can be tweaked and changed a lot. Right now the only point of interest is in getting a preliminary filesystem of appropriate configuration files and mount points. First it's required to create a directory within for the first slave. Each slave needs its own root file system because sharing certain system files will cause permission problems and hard crashes. These directories can be called anything the administrator deems appropriate but the article suggests using the slaves IP addresses as they are unique and not confusing. The static IP of the first slave will be, for instance,  :

Various configuration files in need to be altered to work on the slave. Copy the master's directory onto the new slave root by typing:

Le système de fichiers est encore incomplet, il lui manque différents points de montage. Pour les créer tapez :

Most of these "stubs" should be recognizable; stubs like,  or  will be populated when the slave starts, the others will be mounted later. The file should also be changed to reflect the hostname of the slave. Binaries, libraries and other files will be populated later in this HOWTO right before attempting to boot the slave.

Even though is populated by   later on, the  entry needs to be created. If not, the error message "unable to open initial console" will be encountered.

À propos du serveur DHCP
DHCP signifie Dynamic Host Configuration Protocol (protocole dynamique de configuration des hôtes). Le serveur DHCP est le premier ordinateur contacté par les nœuds esclaves quand ils démarrent par le système PXE via le réseau. La principale fonction d'un serveur DHCP est d'attribuer des adresses IP. Un tel serveur peut attribuer des adresses en se basant sur les adresses MAC des cartes réseau (N.D.T. : l'adresse MAC est censée être unique pour chaque carte sur le marché et est attribuée par le constructeur). Une fois l'adresse attribuée, le serveur DHCP indique au nœud esclave où il peut obtenir son noyau et son système de fichiers préliminaire.

Before getting started
There are several things to make sure of, that they are working properly before beginning. First check the network connectivity:

Make sure there is an eth0 device running. It should look something like this:

It's important that it says MULTICAST, if it doesn't then the kernel will have to be recompiled to include multicast support.

Installer le serveur DHCP
If the network does not already have a DHCP server installed, one needs to be installed now:

If the network already has a DHCP server installed, edit the configuration file to get the PXE boot to function correctly.

Configurer le serveur
There is only one configuration file that needs to be edited before starting the DHCP server:. Copy and edit the provided sample file:

Le fichier de configuration est organisé et indenté comme ceci :

The  block is optional and should be used for IPs that are required to be assigned that belong to the same network topology. At least one  must be declared and the optional   block allows options to be grouped between items. A good example of looks like this:

The IP address after  will be asked for the specified. This IP address should be the IP of the tftp server, usually the same as the master's IP address. The  is relative to the  directory (this is due to the tftp server specific options which will be covered later). Inside the  block, the   option specifies a MAC address, and   assigns a fixed IP address to that particular MAC address. There is a pretty good man page on with options that are beyond the scope of this HOWTO. The man page can be read by typing:

Démarrer le serveur DHCP
Before starting the dhcp initialization script edit the file so that it looks something like this:

The  variable is the device that the DHCP server will be running on, in this case. Adding more arguments to the  variable can be useful for a complex network topology with multiple Ethernet cards. To start the dhcp server type:

To add the dhcp server to the start-up scripts type:

Dépanner le serveur DHCP
To see if a node boots, take a look at. If the node successfully boots, the file should have some lines at the bottom looking like this:

If the following message is encountered it probably means there is something wrong in the configuration file but that the DHCP server is broadcasting correctly.

Every time after changing the configuration file the DHCP server must be restarted. To restart the server type:

À propos du serveur TFTP
TFTP signifie « Trivial File Transfer Protocol ». Le serveur TFTP va fournir un noyau et un système de fichiers aux nœuds esclaves. Tous les noyaux des esclaves et leur système de fichiers seront stockés sur le serveur TFTP. Il est donc recommandé de l'installer sur le nœud maître.

Installer le serveur TFTP
Un serveur TFTP reconnu est celui compris dans le paquet tftp-hpa. Il se trouve qu'il a été écrit par le même auteur que SYSLINUX et ils fonctionnent très bien ensemble. Faites :

Configurer le serveur TFTP
Edit. The tftproot directory needs to specified with  and any command line options with. It should look something like this:

The  option indicates that this server listens in stand alone mode so inetd does not have to be run. The  indicates that log/error messages should be verbose. The  specifies the root of the tftp server.

Démarrer le serveur TFTP
Pour démarrer le serveur tftp tapez :

This should start the tftp server with the options that were specified in the. If this server is to be automatically started at boot type:

À propos de PXELINUX
This section is not required if only Etherboot is being used. PXELINUX is the network bootloader equivalent to LILO or GRUB and will be served via TFTP. It is essentially a tiny set of instructions that tells the client where to locate its kernel and initial filesystem and allows for various kernel options.

Before getting started
Now the file pxelinux.0 is required, which comes in the SYSLINUX package by H. Peter Anvin. This package can be installed by typing:

Configurer PXELINUX
Before starting the tftp server pxelinux needs to be set up. First copy the pxelinux binary into the directory:

Cela va créer un fichier de configuration par défaut pour syslinux. Le binaire cherche son fichier de configuration dans le répertoire. Il commence par chercher un fichier dont le nom est l'adresse IP attribuée au nœud écrite en hexadécimal. Si un tel fichier n'existe pas, enlève successivement le chiffre le plus à droite et regarde si un fichier correspondant existe jusqu'à ce qu'il trouve un fichier ou qu'il n'y ait plus de chiffre. Les version 2.05 et ultérieures de syslinux recherchent d'abord un fichier nommé d'après l'adresse MAC. Si ce fichier n'existe pas, la routine de recherche présentée ci-haut est effectuée. En dernier recours, le fichier est utilisé.

Démarrons avec le fichier file:

The  tag directs pxelinux to the kernel bzImage that was compiled earlier. The  tag appends kernel initialisation options. Since the slave kernel was compiled with , the nfsroot will be specified here. The first IP is the master's IP and the second IP is the directory that was created in to store the slave's initial filesystem.

À propos d'Etherboot
Etherboot boots network boot images from a TFTP server. As the PXE this is equivalent to LILO or GRUB. The  utility enables the creation of different images using different options.

Before getting started
The  (utility for making tagged kernel images useful for netbooting) package is needed to create the Etherboot images. This tool will create a preconfigured kernel image from the original kernel. This contains the boot options as shown further down.

Configurer Etherboot
In this section a simple etherboot image will be created. As the dhcp server gives out the clients root-path in the "option root-path" dhcp.conf, this does not have to be included here. More details can be found in the mknbi manual.

Pour créer une image ELF sur laquelle démarrer qui sait passer les paramètres DHCP et la racine à utiliser au noyau tout en forçant le noyau à demander une adresse IP via DHCP, faites :

Dépanner le processus de démarrage sur réseau
There are a few things that can be done to debug the network boot process. Primarily a tool called  can be used. To install  type:

Now various network traffic can be listened to, to make sure the client/server interactions are functioning. If something isn't working there are a few things that could be checked. First make sure that the client/server is physically connected properly and that the networking cables are not damaged. If the client/server is not receiving requests on a particular port make sure that there is no firewall interference. To listen to interaction between two computers type:

The  command can also be configured to listen on particular port such as the tftp port by typing:

A common error that might be received is: "PXE-E32: TFTP open time-out". This is probably due to firewall issues. If  is being used, it might be worth checking  and  and make sure that they are configured properly. The client should be allowed to connect to the server.

À propos du serveur NFS
NFS stands for Network File System. The NFS server will be used to serve directories to the slave. This part can be somewhat personalized later, but right now all that is wanted is a preliminary slave node to boot diskless.

À propos de Portmapper
Certains services ne sont pas toujours liés au même port, mais utilisent le système d'appel de fonction à distance (les RPC en anglais pour « Remote Procedure Call »). Dans ce cas, lorsqu'un service démarre, il écoute sur un port disponible choisi au hasard et il s'inscrit dans la liste de tels services tenue par le programme portmapper. NFS utilise ce mécanisme et a besoin que le programme portmapper soit actif avant de démarrer.

Before starting
The NFS Server needs kernel level support so if the kernel does not have this, the master's kernel needs to be recompiled. To double check the master's kernel configuration type:

The output should look something like this if the kernel has been properly configured:

Installer le serveur NFS
Le paquet NFS est installé via Portage comme ceci :

Ce paquet comprend le programme portmapper, le serveur nfs et les utilitaires pour les clients NFS. Les dépendances lors de l'initialisation sont automatiquement résolues.

Configurer le serveur NFS
There are three major configuration files that will have to be edited:

Le fichier indique comment, à qui et quoi exporter via NFS. Le fichier /etc/fstab des nœuds esclaves sera modifié pour monter les systèmes de fichiers exportés par le maître.

Le fichier   typique du maître devrait ressembler à ceci :

Le premier champ indique le nom du répertoire à exporter et le suivant spécifie à qui et comment. Le « qui » indique quel nœud peut monter ce répertoire via le réseau et le « comment » liste ce que le nœud peut faire. L'option  interdit l'écriture (=read-only) et   l'autorise. Les options  et no_  sont importantes pour les clients sans disque qui écrivent sur le disque, de manière à ce qu'ils ne soient pas squashés lors qu'ils font des requêtes d'entrée/sortie. Le fichier fstab de l'esclave, : devrait ressembler à ceci :

In this example, master is just the hostname of the master but it could easily be the IP of the master. The first field indicates the directory to be mounted and the second field indicates where. The third field describes the filesystem and should be NFS for any NFS mounted directory. The fourth field indicates various options that will be used in the mounting process (see mount(1) for info on mount options). Some people have had difficulties with soft mount points so here they are made hard mounts, a look into various options should be done to make the cluster more efficient.

The last file that should be edited is which describes a few options for nfs when it is initialised and looks like this:

The  should be changed to the number of diskless nodes on the network.

Démarrer le serveur NFS
The nfs server should be started with its init script located in by typing:

If this script is to be started every time the system boots simply type:

Copier les fichiers manquants
Now the slave's file system will be made in sync with the master's and provide the necessary binaries while still preserving slave specific files.

L'utilisation de rsync -avz, au lieu de cp, permet de copier les liens symboliques et les permissions de fichiers.

Configurer le réseau des nœuds sans disque
In order to prevent the networking initscript from killing the connection to the NFS server, an option needs to be added to on the diskless client's filesystem.

Scripts d'initialisation
Init scripts for slaves are located under for services needed on the diskless nodes. Each slave can be set up and customized here, it all depends on what each slave is meant to do.

Now is a good time to boot the slave and cross some fingers. It works? Congratulations, you are now the proud owner of (a) diskless node(s).