Difference between revisions of "Diskless system"

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(Client configuration: removed deprecated nonsense.)
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{{bc|# umount "$root"}}
{{bc|# umount "$root"}}
{{Note|To update the kernel in this setup, you either need to mount {{ic|/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}}
{{Note|To update the kernel in this setup, you either need to mount {{ic|/srv/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}}

Revision as of 08:21, 8 December 2012

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Merge-arrows-2.pngThis article or section is a candidate for merging with PXE.Merge-arrows-2.png

Notes: needs to be rewritten into sub-articles; duplicated information (Discuss in Talk: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.


Install ISC dhcp.

# pacman -Syu dhcp

Configure ISC DHCP.

# vim /etc/dhcpd.conf
allow booting;
allow bootp;


option domain-name-servers;

    filename "pxelinux.0";

    subnet netmask {
        option routers;
Note: next-server should be the address of the TFTP server; everything else should be changed to match your network


# systemctl start dhcpd


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 /srv/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


Copy the tftp unit files in /usr/lib/systemd/system to /etc/systemd/system; 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/

Next we tell tftpd where the tftp root is: /srv/arch/boot.

# vim /etc/systemd/system/tftpd.service
Description=hpa's original TFTP daemon

ExecStart=/usr/sbin/in.tftpd -s /srv/arch/boot/

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.


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
/srv/arch *(rw,fsid=0,no_root_squash,no_subtree_check,async)
Note: If you're worried about data loss in the event of network failure, replace async with sync--additional options can be found in the NFS article.

Next start NFS.

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


Install nbd.

# pacman -Syu nbd

Configure nbd.

# vim /etc/nbd-server/config
    exportname = /srv/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

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 /srv/arch.img
# mkfs.ext4 /srv/arch.img
# mkdir -p /srv/arch
# mount /srv/arch.img /mnt/arch
Note: Creating a separate filesystem is required for NBD but optional for NFS and can be skipped/ignored, but consider the subtree_check option in the latter case.

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

# export root=/srv/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 mkinitcpio-nfs-utils nfs-utils --arch x86_64

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Add the qemu magic (or link) required to chroot i686 from a x86_64 host (Discuss in Talk:Diskless system#)

Replace x86_64 with i686 as appropriate for your target hardware.

Note: If you're using NBD, you'll want to replace nfs-utils with mkinitcpio-nbdAUR; however mkinitcpio-nfs-utils is still required (ipconfig used in early-boot is provided only by the latter).

Next, edit "$root/etc/mkinitcpio.conf" and add nfsv4 to the MODULES array, and add net after udev to the HOOKS array.

Note: net indeed doesn't directly support nfsv4 root, but that is only due to its use of nfsmount; it is, however, luckily trivial to replace it with mount.nfs4
# vim "$root/etc/mkinitcpio.conf"
HOOKS="base udev net autodetect filesystems"

You also need to make trivial modifications to the net hook; see this patch. You'll want to rename your patched version so it doesn't get overwritten when mkinitcpio-nfs-utils is updated on the client installation.

Note: Add nbd after the net hook if you are using NBD; you also should exclude BINARIES

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" \

Client configuration

In addition to the setup mentioned here, you should also set up your hostname, timezone, locale, and keymap, and follow any other relevant parts of the Installation Guide.


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 ip=:::::eth0:dhcp nfsroot=

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

append initrd=initramfs-linux.img ip=:::::eth0:dhcp nbd_host= nbd_name=arch
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

Client boot


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 $root/boot from the client installation to your tftp root (i.e. /srv/boot).

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


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

syslinux.org: pxelinux FAQ