PXE - ArchWiki

# PXE

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This article or section is a candidate for moving to Preboot Execution Environment.

Notes: ALSA is named Advanced Linux Sound Architecture. (Discuss in Talk:PXE#)

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- 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

Get the latest official install media from download page.

Next mount the image:

    # mkdir -p /mnt/archiso
    # mount -o loop,ro archlinux-2017.12.01-x86_64.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).

The Arch ISO currently only supports BIOS-style PXE booting. See FS#50188 for more information.

Arch Netboot does support UEFI-style booting if you require that. Rest of this page focuses on the ISO however.

### 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 the dnsmasq package.

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/
    dhcp-option-force=66,192.168.0.1
    enable-tftp
    tftp-root=/mnt/archiso

Start `dnsmasq.service`.

### HTTP

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

First, install the darkhttpd package.

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/

Note that it is important that the server is running on port `80`. If you start darkhttpd without root access it will default to `8080`. The client will try to access port 80 and the boot will fail.

## 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.service -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, where you can select Boot Arch Linux (x86_64) (HTTP).

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 the normal live system root zsh prompt.

### 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 stop `dnsmasq.service` and get a new lease on the install target, as appropriate for your network layout.

You can also kill darkhttpd; the target has already downloaded the root filesystem, so it is 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 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 #Preparation. 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

Install the nbd package and configure it:

    /etc/nbd-server/config

    [generic]
    [archiso]
        readonly = true
        exportname = /srv/archlinux-2017.12.01-x86_64.iso

Start `nbd.service`.

### Existing PXE Server

If you have an existing PXE server with a PXELINUX system setup (e.g. a combination of DHCP and TFTP), you can add the following menu items to your `/tftpboot/pxelinux.cfg/default` file in order to boot Arch via your preferred method:

    LABEL archlinux
            MENU LABEL Arch Linux x86_64
            LINUX /path/to/extracted/Arch/ISO/arch/boot/x86_64/vmlinuz
            INITRD /path/to/extracted/Arch/ISO/arch/boot/intel_ucode.img,/path/to/extracted/Arch/ISO/arch/boot/amd_ucode.img,/path/to/extracted/Arch/ISO/arch/boot/x86_64/archiso.img
            APPEND archisobasedir=arch archiso_http_srv=http://httpserver/path/to/extracted/Arch/ISO/
            SYSAPPEND 3
            TEXT HELP
            Arch Linux 2018.09.01 x86_64
            ENDTEXT

You can replace `archiso_http_srv` with `archiso_nfs_srv` for NFS or `archiso_nbd_srv` for NBD (see usage examples in `arch/boot/syslinux/archiso_pxe.cfg` file resided on ArchLinux iso). Whichever method you choose, you must pass `ip=` parameter to instruct the kernel to bring up the network interface before it attempts to mount the installation medium over the network. Passing `BOOTIF=` is required when there are several wired interfaces on the client side and/or you want resolv.conf to be already configured inside booted archiso. You can use sysappend mask 3 (which is 1+2) to pass these parameters automatically. For available boot parameters see README.bootparams.

### Low memory systems

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.

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

## Troubleshooting

### DHCP interface rename bug

FS#36749 causes default predictable network interface renaming to fail and then dhcp client to fail because of it. A workaround is to add the kernel boot parameter `net.ifnames=0` to disable predictable interface names.

### VirtualBox cannot boot while real machine can

When using VirtualBox to test your configuration, virtual machine is stucked at

       Probing EDD (edd=off to disable)... ok

But pxe booting with real machine works fine. The problem may be because you have set several cpu cores to your client machine, and you set its type as Other and version as Unknown (64 bit). So VirtualBox does not know which paravirtualization interface to use by default. Adding loglevel=7 kernel parameter lets you see that machine was actually stuck at

       [    0.063697] smp: Bringing up secondary CPUs...
       [    0.103768] x86: Booting SMP configuration:

To resolve this, either use one cpu core, or go to machine settings -> System -> Acceleration and set one of the following paravirtualization interface: Minimal, Hyper-V, KVM.

### VirtualBox falls out to EFI shell

Currently VirtualBox does not support PXE booting in UEFI mode. See this. You can try qemu instead. Alternatively you can use VMware Workstation 15.0.2 (it supports uefi pxe boot) or just a real hardware.

Categories:

- Installation process
- Networking
- Boot process

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