Diskless system

Contrast to the official installation guide, which concentrates on an arch installation on local storage, here the installation is to be placed on network storage.

Server configuration

You will need a DHCP server to setup networking, as well as a TFTP server to transfer the boot image (a requirement of all PXE option roms). Unlike PXE which is designed for quick-and-dirty/temporary setups to boot installation media, here you're actually doing a network installation, which is more-permanent, and thus calls for doing things properly.

DHCP

Install ISC dhcp.

# pacman -Syu dhcp

Configure ISC DHCP.

# vim /etc/dhcpd.conf

allow booting;
allow bootp;

authoritative;

option domain-name-servers 10.0.0.1;

group 
{
    next-server 10.0.0.1;
    filename "pxelinux.0";

    subnet 10.0.0.0 netmask 255.255.255.0 {
        option routers 10.0.0.1;
        range 10.0.0.128 10.0.0.254;
    }
}

Note: next-server should be the address of the TFTP server; everything else should be changed to match your network

Start ISC DHCP.

# systemctl start dhcpd

TFTP

The TFTP server will be used to transfer the kernel, initramfs, and pxelinux to the client.

Install tftp-hpa.

# pacman -Syu tftp-hpa

Note: Change /mnt/arch/boot to /mnt/boot if you're going to use NBD, because you'll be unable to mount your root filesystem while in use

Configuration

Copy the tftp unit files in /usr/lib/systemd to /etc/systemd; the former gets overwritten when systemd is updated. The systemd article talks in more detail about customizing unit files.

# cp /usr/lib/systemd/system/tftpd.s* /etc/systemd/system/

# vim /etc/systemd/system/tftpd.service

[Unit]
Description=hpa's original TFTP daemon

[Service]
ExecStart=/usr/sbin/in.tftpd -s /mnt/arch/boot/
StandardInput=socket
StandardOutput=inherit
StandardError=journal

Start tftpd :

# systemctl enable tftpd.socket
# systemctl start tftpd.socket

Network storage

The primary difference between using NFS and NBD is while with both you can in fact have multiple clients using the same installation, with NBD (by the nature of manipulating a filesystem directly) you'll need to use the copyonwrite mode to do so, which ends up discarding all writes on client disconnected. In some situations however, this might be highly desirable.

NFS

Install nfs-utils on the server.

# pacman -Syu nfs-utils

You'll need to add the root of your arch installation to your NFS exports.

# vim /etc/exports

/mnt/arch *(rw,fsid=0,no_root_squash,no_subtree_check,async)

Next start NFS.

# systemctl start nfsd.service rpc-idmapd.service rpc-mountd.service rpcbind.service

Or if you still use sysvinit,

# rc.d start rpcbind nfs-common nfs-server

Additional information can be found in the NFS article.

NBD

Install nbd.

# pacman -Syu nbd

Configure nbd.

# vim /etc/nbd-server/config

[generic]
[arch]
    exportname = /mnt/arch.img
    copyonwrite = false

Note: Set copyonwrite to true if you want to have multiple clients using the same NBD share simultaneously; refer to man 5 nbd-server for more details.

Start nbd.

# systemctl start nbd

Or if you still use sysvinit,

# rc.d start nbd-server

Client installation

Directory setup

Create a sparse file of at least 5 gigabytes, and create an ext4 filesystem on it (you can of course also use a real block device or LVM if you so desire).

# truncate -s 5G /mnt/arch.img
# mkfs.ext4 /mnt/arch.img
# mkdir -p /mnt/arch
# mount /mnt/arch.img /mnt/arch

Note: Creating a separate filesystem is required for NBD but optional for NFS and can be skipped/ignored

First, create a directory that will contain the Arch installation; replace /mnt/arch with wherever you'd like to put your installation.

# export root=/mnt/arch
# mkdir -p "$root/{proc,sys,run,tmp}"
# mkdir -p "$root/dev/{pts,shm}"

This also creates the directories that will be used for the API filesystem mountpoints later. Next we create the directory that pacman stores its database.

# mkdir -p "$root/var/lib/pacman"

Bootstrapping installation

Note: You can also use arch-chroot and pacstrap from arch-install-scripts rather than chroot and pacman directly

Mount the Linux API filesystems.

# mount -t proc proc "$root/proc" -o nosuid,noexec,nodev
# mount -t sysfs sys "$root/sys" -o nosuid,noexec,nodev
# mount -t devtmpfs udev "$root/dev" -o mode=0755,nosuid
# mount -t devpts devpts "$root/dev/pts" -o mode=0620,gid=5,nosuid,noexec

Install the essential packages needed.

# pacman -Syu --root "$root" --dbpath "$root/var/lib/pacman" base base-devel --arch x86_64

Replace x86_64 with i686 as appropriate for your target hardware.

You'll need to install either mkinitcpio-nfs-utils or mkinitcpio-nbd^AUR depending on whether you are using NFS or NBD.

Next, edit "$root/etc/mkinitcpio.conf" and add nfsv3 to the MODULES array, and add net after udev to the HOOKS array.

# vim "$root/etc/mkinitcpio.conf"

MODULES="nfsv3"
HOOKS="base udev net autodetect filesystems"

Note: Add nbd after the net hook if you are using NBD.

The initramfs now needs to be rebuilt; the easiest way to do this is chroot.

# chroot "$root" /bin/bash
(chroot) # mkinitcpio -p linux
(chroot) # exit

Finally, cleanup by unmounting all of the virtual filesystems we mounted earlier.

# umount \
    "$root/dev/pts" \
    "$root/dev" \
    "$root/sys" \
    "$root/proc"

Client configuration

In addition to the setup mentioned here, you should also set up your hostname, timezone, locale, and keymap.

Pxelinux

Install syslinux.

# pacman -Syu syslinux

Copy the pxelinux bootloader (provided by the syslinux package) to the boot directory of the client.

# cp /usr/lib/syslinux/pxelinux.0 "$root/boot"
# mkdir "$root/boot/pxelinux.cfg"

We also created the pxelinux.cfg directory, which is where pxelinux searches for configuration files by default. Because we don't want to discriminate between different host MACs, we then create the default configuration.

# vim "$root/boot/pxelinux.cfg/default"

default linux

label linux
kernel vmlinuz-linux
append initrd=initramfs-linux.img rootfstype=nfs root=/dev/nfs nfsroot=10.0.0.1:/mnt/arch,v4,rsize=16384,wsize=16384 ip=:::::eth0:dhcp

Or if you are using NBD, use the following append line:

# append initrd=initramfs-linux.img root=/dev/nbd0 nbd_host=10.0.0.1 nbd_name=arch ip=:::::eth0:dhcp

Note: You will need to change nbd_host and/or nfsroot, respectively, to match your network configuration (the address of the NFS/NBD server)

The pxelinux configuration syntax identical to syslinux; refer to the upstream documentation for more information.

The kernel and initramfs will be transferred via TFTP, so the paths to those are going to be relative to the TFTP root. Otherwise, the root filesystem is going to be the NFS mount itself, so those are relative to the root of the NFS server.

VFS mountpoints

Add hacks to your fstab for the root filesystem and devpts.

# vim "$root/etc/fstab"

none    /           none
none    /dev/pts    devpts    gid=5,mode=620    0 0

Late-boot networking

This is to prevent the client from trying to reconnect the network and killing itself. Any disconnect of the network and your client will freeze.

One way to fix this is by running dhcpcd with the -s option to use the existing lease obtained in early-boot instead of requesting a new one.

# vim "$root/etc/conf.d/dhcpcd"

DHCPCD_ARGS=" -s $(ifconfig eth0 | grep -o '[0-9]*\.[0-9\.]*' | head -n1)"

# vim "$root/etc/rc.conf"

NETWORK_PERSIST="yes"

Client boot

NBD

If you're using NBD, you'll need to umount the arch.img before/while you boot your client.

This makes things particularly interesting when it comes to kernel updates. You can't have your client filesystem mounted while you're booting a client, but that also means you need to use a kernel separate from your client filesystem in order to build it.

You'll need to first copy /boot from the client installation (make sure your TFTP root matches this).

# cp -r "$root/boot" /mnt/boot

You'll then need to umount $root before you start the client.

# umount "$root"

Note: To update the kernel in this setup, you either need to mount /mnt/boot using NFS in fstab on the client (prior to doing the kernel update) or mount your client filesystem after the client has disconnected from NBD

References

kernel.org: Mounting the root filesystem via NFS (nfsroot)

syslinux.org: pxelinux FAQ