Diskless nodes/es

Este CÓMO le ayudará a crear y poner en marcha nodos sin disco en Gentoo Linux

Acerca de este CÓMO
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.

¿Qué es una máquina sin disco?
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.

Antes de empezar
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.

Acerca de los núcleos
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 HOWTO.

Configurar el núcleo maestro
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:

Si se necesita filtrado de paquetes, añada el resto como módulos más tarde. Asegúrese de leer el Manual de seguridad Gentoo Capítulo 12 acerca de los Cortafuegos para saber cómo configurarlo de manera adecuada.

Una vez haya reconfigurado el núcleo, necesitará reconstruirlo:

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.

Acerca del núcleo esclavo
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.

Para evitar cualquier confusión y desperdicio de tiempo es una buena idea hacer una copia de seguridad del fichero de configuración del núcleo maestro tecleando:

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:

Ahora entremos a la interfaz visual de configuración tecleando:

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:

Configurar un sistema de ficheros esclavo preliminar
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 author 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:

Este sistema de ficheros no está listo aún porque necesita varios puntos de montaje y directorios. Para crearlos, teclee:

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.

Acerca del servidor DHCP
DHCP son las iniciales (en inglés) de Protocolo Dinámico de Configuración del Anfitrión. El servidor DHCP es la primera máquina con la que el esclavo se comunicará en el momento del arranque PXE. El propósito principal del servidor DHCP es el de asignar las direcciones IP. El servidor DHCP puede asignar direcciones IP basándose en la dirección MAC Ethernet del anfitrión. Una vez que el esclavo tiene su dirección IP, el servidor DHCP le dirá donde conseguir su sistema de ficheros inicial y el núcleo.

Antes de empezar
There are several things to make sure of, that they are working properly before beginning. First check the network connectivity:

Asegúrese de tener un dispositivo "eth0" funcionando. La salida de la orden anterior debe parecerse algo a esto:

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

Instalar el servidor 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.

Configurar el servidor DHCP
There is only one configuration file that needs to be edited before starting the DHCP server:. Copy and edit the provided sample file:

La disposición general con sangrías del fichero se asemeja a esta:

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:

Iniciar el servidor 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:

Solucionar problemas con el servidor 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:

Acerca del servidor DHCP
TFTP son las (en inglés) siglas del Protocolo Trivial de Transferencia de Archivos. El servidor TFTP les va a dar a los esclavos el núcleo y un sistema de fichero inicial. Todos los núcleos esclavos y sistemas de ficheros deben estar almacenados en el servidor TFTP, así que es una buena idea hacer que el maestro también sea el servidor TFTP.

Instalar el servidor TFTP
Un servidor tftp altamente recomendado está disponible en el paquete tftp-hpa. Este servidor lo escribió el autor de SYSLINUX y funciona muy bien con pxelinux. Para instalarlo simplemente escriba:

Configurar el servidor 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.

Iniciar el servidor TFTP
Para iniciar el servidor tftp, escriba:

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:

Acerca 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:

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

Esto creará el fichero de configuración por defecto del cargador de arranque. El binario buscará en el directorio un fichero cuyo nombre sea la dirección IP del cliente en hexadecimal. Si no lo encuentra, eliminará el dígito más a la derecha del nombre del fichero y lo volverá a intentar hasta que se terminen los dígitos. Las versiones a partir de la 2.05 de syslinux realizan en primer lugar una búsqueda de un fichero cuyo nombre sea la dirección MAC. Si no se encuentra, ejecuta la rutina ya descrita. Si no se localiza ningún fichero, se utiliza.

Comencemos con el fichero :

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.

Acerca de 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.

Configurar 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.

Crear la imagen de arranque. La siguiente orden creará la imagen ELF de arranque capaz de pasar el dhcp y la dirección del directorio raíz al núcleo. También obliga al núcleo a buscar en la red un servidor dhcp.

Solucionar problemas en el proceso de arranque por red
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.

Acerca del servidor 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.

Acerca de Portmapper
Algunos servicios cliente/servidor no escuchan en un puerto en particular, en cambio utilizan RPCs (llamadas a procedimientos remotos). Cuando se inicializa un servicio, escucha en un puerto al azar y luego registra este puerto en la utilidad Portmapper. NFS utiliza RPCs y por lo tanto requiere tener a Portmapper corriendo antes de su inicio.

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:

Instalar el servidor NFS
El paquete NFS se puede instalar mediante portage escribiendo:

Este paquete instalará la utilidad portmapping, el servidor nfs, y las utilidades nfs del cliente y automáticamente gestionará la inicialización de las dependencias.

Configurar el servidor NFS
There are three major configuration files that will have to be edited:

El fichero especifica como, a quién y qué se debe exportar a través de NFS. Se debe modificar el fstab del esclavo para que pueda montar el sistema de ficheros NFS que el maestro está exportando.

Un fichero típico del maestro se parece a esto:

El primer campo indica el directorio que será exportado y el siguiente indica a quién y cómo. Este campo puede dividirse en dos partes: a quién se le debe permitir montar ese directorio en particular, y qué puede hacer el cliente con él:  de solo lectura,   de lectura y escritura;   y   son importantes para clientes sin disco que escriben en el disco de manera que no sean "apretados" al hacer pedidos de E/S. El fichero fstab del esclavo,, debe ser similar a este:

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.

Iniciar el servidor 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:

Copiar los ficheros que faltan
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.

Configurar la red sin disco
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.

Guiones de inicialización
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.

Ahora es un buen momento para iniciar los esclavos y cruzar los dedos. ¿Funciona? Felicidades, ahora es un orgulloso poseedor de un(os) nodo(s) sin disco.