117 lines
4.3 KiB
Markdown
117 lines
4.3 KiB
Markdown
# PXE-booting with iPXE
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## UEFI
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iPXE supports UEFI and so do we. This requires the ``ipxe.efi`` boot image.
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Instructions how to copy the necessary grub files to the tftp server:
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https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/installation_guide/chap-installation-server-setup#sect-network-boot-setup-uefi
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(alternatively one can also copy the files from the /boot/efi/EFI/redhat/ directory of an installed system)
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```
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[root@ tmp]# cd /tmp
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[root@ tmp]# curl -OL http://repos.psi.ch/rhel9/iso/rhel-baseos-9.1-x86_64-dvd/BaseOS/Packages/shim-x64-15.6-1.el9.x86_64.rpm
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% Total % Received % Xferd Average Speed Time Time Time Current
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Dload Upload Total Spent Left Speed
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100 471k 100 471k 0 0 92.0M 0 --:--:-- --:--:-- --:--:-- 92.0M
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[root@lx-repos-01 tmp]# curl -LO http://repos.psi.ch/rhel9/iso/rhel-baseos-9.1-x86_64-dvd/BaseOS/Packages/grub2-efi-x64-2.06-46.el9.x86_64.rpm
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% Total % Received % Xferd Average Speed Time Time Time Current
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Dload Upload Total Spent Left Speed
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100 1333k 100 1333k 0 0 8550k 0 --:--:-- --:--:-- --:--:-- 8550k
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[root@ tmp]# rpm2cpio shim-x64-15.6-1.el9.x86_64.rpm | cpio -dimv
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./boot/efi/EFI/BOOT/BOOTX64.EFI
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./boot/efi/EFI/BOOT/fbx64.efi
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./boot/efi/EFI/redhat/BOOTX64.CSV
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./boot/efi/EFI/redhat/mmx64.efi
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./boot/efi/EFI/redhat/shim.efi
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./boot/efi/EFI/redhat/shimx64-redhat.efi
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./boot/efi/EFI/redhat/shimx64.efi
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9232 blocks
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[root@ tmp]# rpm2cpio grub2-efi-x64-2.06-46.el9.x86_64.rpm | cpio -dimv
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./boot/efi/EFI/redhat/grubx64.efi
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./boot/grub2/fonts
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./boot/grub2/fonts/unicode.pf2
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./boot/grub2/grubenv
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./boot/loader/entries
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./etc/dnf/protected.d/grub2-efi-x64.conf
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./etc/grub2-efi.cfg
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./etc/grub2.cfg
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9612 blocks
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[root@ tmp]# ls boot/efi/EFI/redhat/
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BOOTX64.CSV grubx64.efi mmx64.efi shim.efi shimx64.efi shimx64-redhat.efi
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[root@ tmp]# ls -la boot/efi/EFI/redhat/
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total 6088
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drwxr-xr-x. 2 root root 122 Mar 1 16:16 .
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drwxr-xr-x. 4 root root 32 Mar 1 16:16 ..
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-rwx------. 1 root root 108 Jun 7 2022 BOOTX64.CSV
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-rwx------. 1 root root 2524792 Aug 25 2022 grubx64.efi
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-rwx------. 1 root root 856528 Jun 7 2022 mmx64.efi
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-rwx------. 1 root root 946736 Jun 7 2022 shim.efi
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-rwx------. 1 root root 946736 Jun 7 2022 shimx64.efi
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-rwx------. 1 root root 938808 Jun 7 2022 shimx64-redhat.efi
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[root@ tmp]#
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```
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## Process
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When a system PXE boots, the DHCP server will boot either pxelinux in legacy
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mode or grub on UEFI. It is still possible to load ipxe from either of these.
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With the right option, the boot process is pointed to ``sysdb.psi.ch`` and one
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of the following boot images:
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- `ipxe.efi` for systems using UEFI
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- `ipxe.lkrn` for all other systems
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The system downloads the image and executes it.
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The image contains a small iPXE script, which makes iPXE retrieve its actual
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configuration from a web service running (usually) on `sysdb.psi.ch`.
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Specifically, it queries the URL
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`https://sysdb.psi.ch/ipxe/v1/config?mac=<MAC>`, where `<MAC>` is the MAC
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address of the interface used by iPXE.
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The web service on ``sysdb.psi.ch`` will generate the iPXE configuration on the
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fly, depending on whether the system is supposed to be reinstalled and if so,
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which distribution it is supposed to use. The menu offers other options as well,
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e.g. an interactive iPXE shell and a memory test.
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## Sequence Diagram of the UEFI Boot Process
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## Sequence Diagram of the BIOS (Legacy) Boot Process
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## Building the iPXE boot image
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The steps for building an iPXE image are
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1. Clone `git@git.psi.ch:linux-infra/ipxe-build.git`
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2. Change into the new directory
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3. Run the `refresh-ipxe.sh` script. This will check out the iPXE source code
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mirror from `git.psi.ch`.
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4. Run the `build.sh` script. This will use the named configurations in the
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`ipxe-build` repository to compile two iPXE images: `src/bin/ipxe.lkrn`
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(legacy boot) and `src/bin-x86_64-efi/ipxe.efi` (UEFI).
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As described above, we use an iPXE boot image with an embedded script looking
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roughly like the following
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```
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#!ipxe
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dhcp && goto dhcp_succeeded
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shell
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#prompt for network info
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:dhcp_succeeded
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chain http://sysdb.psi.ch/ipxe/v1/config?mac=${netX/mac}
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```
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