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doc: Document new bootloader grub-efi-netboot-bootloader.

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* doc/guix.texi (Bootloader Configuration)[bootloader]: Add
grub-efi-netboot-bootloader.
[target]: Document TFTP root directory for grub-efi-netboot-bootloader.

Signed-off-by: Danny Milosavljevic <dannym@scratchpost.org>
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Stefan 2020-09-20 00:55:56 +02:00 • committed by Danny Milosavljevic
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@ -28682,7 +28682,15 @@ The type of a bootloader configuration declaration.
@cindex BIOS, bootloader
The bootloader to use, as a @code{bootloader} object. For now
@code{grub-bootloader}, @code{grub-efi-bootloader},
@code{extlinux-bootloader} and @code{u-boot-bootloader} are supported.
@code{grub-efi-netboot-bootloader}, @code{extlinux-bootloader} and
@code{u-boot-bootloader} are supported.
@cindex ARM, bootloaders
@cindex AArch64, bootloaders
Available bootloaders are described in @code{(gnu bootloader @dots{})}
modules. In particular, @code{(gnu bootloader u-boot)} contains definitions
of bootloaders for a wide range of ARM and AArch64 systems, using the
@uref{https://www.denx.de/wiki/U-Boot/, U-Boot bootloader}.
@vindex grub-efi-bootloader
@code{grub-efi-bootloader} allows to boot on modern systems using the
@ -28694,12 +28702,52 @@ when you boot it on your system.
@code{grub-bootloader} allows you to boot in particular Intel-based machines
in ``legacy'' BIOS mode.
@cindex ARM, bootloaders
@cindex AArch64, bootloaders
Available bootloaders are described in @code{(gnu bootloader @dots{})}
modules. In particular, @code{(gnu bootloader u-boot)} contains definitions
of bootloaders for a wide range of ARM and AArch64 systems, using the
@uref{https://www.denx.de/wiki/U-Boot/, U-Boot bootloader}.
@vindex grub-efi-netboot-bootloader
@code{grub-efi-netboot-bootloader} allows you to boot your system over network
through TFTP. In combination with an NFS root file system this allows you to
build a diskless Guix system.
The installation of the @code{grub-efi-netboot-bootloader} generates the content
of the TFTP root directory at @code{target}
(@pxref{Bootloader Configuration, @code{target}}), to be served by a TFTP server.
You may want to mount your TFTP server directory onto @code{target} to move the
required files to the TFTP server automatically.
If you plan to use an NFS root file system as well (actually if you mount the
store from an NFS share), then the TFTP server needs to serve the file
@file{/boot/grub/grub.cfg} and other files from the store (like GRUBs background
image, the kernel (@pxref{operating-system Reference, @code{kernel}}) and the
initrd (@pxref{operating-system Reference, @code{initrd}})), too. All these
files from the store will be accessed by GRUB through TFTP with their normal
store path, for example as
@file{tftp://tftp-server/gnu/store/…-initrd/initrd.cpio.gz}.
Two symlinks are created to make this possible. The first symlink is
@code{target}@file{/efi/Guix/boot/grub/grub.cfg} pointing to
@file{../../../boot/grub/grub.cfg},
where @code{target} may be @file{/boot}. In this case the link is not leaving
the served TFTP root directory, but otherwise it does. The second link is
@code{target}@file{/gnu/store} and points to @file{../gnu/store}. This link
is leaving the served TFTP root directory.
The assumption behind all this is that you have an NFS server exporting the root
file system for your Guix system, and additionally a TFTP server exporting your
@code{target} directory—usually @file{/boot}—from that same root file system for
your Guix system. In this constellation the symlinks will work.
For other constellations you will have to program your own bootloader installer,
which then takes care to make necessary files from the store accessible through
TFTP, for example by copying them into the TFTP root directory at @code{target}.
It is important to note that symlinks pointing outside the TFTP root directory
may need to be allowed in the configuration of your TFTP server. Further the
store link exposes the whole store through TFTP. Both points need to be
considered carefully for security aspects.
Beside the @code{grub-efi-netboot-bootloader}, the already mentioned TFTP and
NFS servers, you also need a properly configured DHCP server to make the booting
over netboot possible. For all this we can currently only recommend you to look
for instructions about @acronym{PXE, Preboot eXecution Environment}.
@item @code{target}
This is a string denoting the target onto which to install the
@ -28710,7 +28758,9 @@ The interpretation depends on the bootloader in question. For
the bootloader @command{installer} command, such as @code{/dev/sda} or
@code{(hd0)} (@pxref{Invoking grub-install,,, grub, GNU GRUB Manual}). For
@code{grub-efi-bootloader}, it should be the mount point of the EFI file
system, usually @file{/boot/efi}.
system, usually @file{/boot/efi}. For @code{grub-efi-netboot-bootloader},
@code{target} should be the mount point corresponding to the TFTP root
directory of your TFTP server.
@item @code{menu-entries} (default: @code{()})
A possibly empty list of @code{menu-entry} objects (see below), denoting