PXE - ArchWiki

# PXE

Related articles

- Diskless System

From Wikipedia:Preboot Execution Environment:

  The Preboot eXecution Environment (PXE, also known as Pre-Execution Environment; sometimes pronounced "pixie") is an environment to boot computers using a network interface independently of data storage devices (like hard disks) or installed operating systems.

In this guide, PXE is used to boot the installation media with an appropriate option-rom that supports PXE on the target. This works well when you already have a server set up.

## Preparation

Download the latest official install media from here.

Next mount the image:

    # mkdir -p /mnt/archiso
    # mount -o loop,ro archlinux-2013.11.01-dual.iso /mnt/archiso

## Server setup

You will need to setup a DHCP, TFTP, and HTTP server to configure networking, load pxelinux/kernel/initramfs, and finally load the root filesystem (respectively).

### Network

Bring up your wired NIC, and assign it an address appropriately.

    # ip link set eth0 up
    # ip addr add 192.168.0.1/24 dev eth0

### DHCP + TFTP

You will need both a DHCP and TFTP server to configure networking on the install target and to facilitate the transfer of files between the PXE server and client; dnsmasq does both, and is extremely easy to set up.

Install dnsmasq from official repositories.

Configure dnsmasq:

    # /etc/dnsmasq.conf

    port=0
    interface=eth0
    bind-interfaces
    dhcp-range=192.168.0.50,192.168.0.150,12h
    dhcp-boot=/arch/boot/syslinux/lpxelinux.0
    dhcp-option-force=209,boot/syslinux/archiso.cfg
    dhcp-option-force=210,/arch/
    enable-tftp
    tftp-root=/mnt/archiso

Start the `dnsmasq` systemd service.

### HTTP

Thanks to recent changes in archiso, it is now possible to boot from HTTP (archiso_pxe_http initcpio hook) or NFS (archiso_pxe_nfs initcpio hook); among all alternatives, darkhttpd is by far the most trivial to setup (and the lightest-weight).

First, install darkhttpd from official repositories.

Then start darkhttpd using our `/mnt/archiso` as the document root:

    # darkhttpd /mnt/archiso

    darkhttpd/1.8, copyright (c) 2003-2011 Emil Mikulic.
    listening on: http://0.0.0.0:80/

## Installation

For this portion you will need to figure out how to tell the client to attempt a PXE boot; in the corner of the screen along with the normal post messages, usually there will be some hint on which key to press to try PXE booting first. On an IBM x3650 F12 brings up a boot menu, the first option of which is Network; on a Dell PE 1950/2950 pressing F12 initiates PXE booting directly.

### Boot

Looking at journald on the PXE server will provide some additional insight to what exactly is going on during the early stages of the PXE boot process:

    # journalctl -u dnsmasq -f

    dnsmasq-dhcp[2544]: DHCPDISCOVER(eth1) 00:1a:64:6a:a2:4d
    dnsmasq-dhcp[2544]: DHCPOFFER(eth1) 192.168.0.110 00:1a:64:6a:a2:4d
    dnsmasq-dhcp[2544]: DHCPREQUEST(eth1) 192.168.0.110 00:1a:64:6a:a2:4d
    dnsmasq-dhcp[2544]: DHCPACK(eth1) 192.168.0.110 00:1a:64:6a:a2:4d
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/pxelinux.0 to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/whichsys.c32 to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso_pxe_choose.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/ifcpu64.c32 to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso_pxe_both_inc.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso_head.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso_pxe32.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso_pxe64.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/archiso_tail.cfg to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/vesamenu.c32 to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/syslinux/splash.png to 192.168.0.110

After you load `pxelinux.0` and `archiso.cfg` via TFTP, you will (hopefully) be presented with a syslinux boot menu with several options, two of which are of potential usefulness to us.

Select either Boot Arch Linux (x86_64) (HTTP) or Boot Arch Linux (i686) (HTTP) depending on your CPU architecture.

Next the kernel and initramfs (appropriate for the architecture you selected) will be transferred, again via TFTP:

    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/x86_64/vmlinuz to 192.168.0.110
    dnsmasq-tftp[2544]: sent /mnt/archiso/arch/boot/x86_64/archiso.img to 192.168.0.110

If all goes well, you should then see activity on darkhttpd coming from the PXE-target; at this point the kernel would be loaded on the PXE-target, and in init:

    1348347586 192.168.0.110 "GET /arch/aitab" 200 678 "" "curl/7.27.0"
    1348347587 192.168.0.110 "GET /arch/x86_64/root-image.fs.sfs" 200 107860206 "" "curl/7.27.0"
    1348347588 192.168.0.110 "GET /arch/x86_64/usr-lib-modules.fs.sfs" 200 36819181 "" "curl/7.27.0"
    1348347588 192.168.0.110 "GET /arch/any/usr-share.fs.sfs" 200 63693037 "" "curl/7.27.0"

After the root filesystem is downloaded via HTTP, you will eventually end up at a root zsh prompt with that fancy grml config.

### Post-boot

Unless you want all traffic to be routed through your PXE server (which will not work anyway unless you set it up properly), you will want to kill dnsmasq and get a new lease on the install target, as appropriate for your network layout.

    # systemctl stop dnsmasq.service

You can also kill darkhttpd; the target has already downloaded the root filesystem, so it's no longer needed. While you are at it, you can also unmount the installation image:

    # umount /mnt/archiso

At this point you can follow the official installation guide.

## Alternate Methods

As implied in the syslinux menu, there are several other alternatives:

### NFS

You will need to set up an NFS server with an export at the root of your mounted installation media, which would be `/mnt/archiso` if you followed the earlier sections of this guide. After setting up the server, add the following line to your `/etc/exports` file:

    /etc/exports

    /mnt/archiso 192.168.0.0/24(ro,no_subtree_check)

If the server was already running, re-export the filesystems with `exportfs -r -a -v`.

The default settings in the installer expect to find the NFS at `/run/archiso/bootmnt`, so you will need to edit the boot options. To do this, press Tab on the appropriate boot menu choice and edit the `archiso_nfs_srv` option accordingly:

    archiso_nfs_srv=${pxeserver}:/mnt/archiso

Alternatively, you can use `/run/archiso/bootmnt` for the entire process.

After the kernel loads, the Arch bootstrap image will copy the root filesystem via NFS to the booting host. This can take a little while. Once this completes, you should have a running system.

### NBD

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Install nbd and configure it:

    # vim /etc/nbd-server/config

    [generic]
    [archiso]
        readonly = true
        exportname = /srv/archlinux-2013.02.01-dual.iso

### Low memory

Note: As this requires loop-mounting squashfs from a mounted remote filesystem, `copytoram=n` and `archiso_pxe_http` are mutually exclusive.

The `copytoram` initramfs option can be used to control whether the root filesystem should be copied to ram in its entirety in early-boot.

It highly recommended to leave this option alone, and should only be disabled if entirely necessary (systems with less than ~256MB physical memory). Append `copytoram=n` to your kernel line if you wish to do so.

Categories:

- Getting and installing Arch
- Networking
- Boot process