259 lines
12 KiB
Plaintext
259 lines
12 KiB
Plaintext
! Appendix
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!! Troubleshooting
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Many common problems are answered in the FAQ document, so if you experience
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problems please check whether the [[http://crux.nu/Main/Faq | CRUX FAQ]]
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contains answers to your questions already.
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If you have further questions, there's a dedicated mailing list for CRUX, and an
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IRC channel. Actual information about these can be found on the [[Community]]
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page.
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[[#grubcfg-manually]]
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!! Writing a grub config file by hand
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If %fn%grub-mkconfig%% does not work (eg., because you saved the kernel image
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under a non-standard name), a grub.cfg file can be created manually. For more
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information see the GRUB manual at [[http://www.gnu.org/software/grub/manual/]].
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A simple example configuration might look like the following:
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[@
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# Display the menu for 10 seconds
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set timeout=10
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# Boot the first entry by default
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set default=0
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# Boot entries follow
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# Default CRUX boot entry
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menuentry "CRUX 3.7" {
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linux (hd0,msdos2)/boot/vmlinuz-5.15.55 root=/dev/sda2 quiet
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}
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# Single-user recovery entry
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menuentry "CRUX 3.7 single-user mode" {
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linux (hd0,msdos2)/boot/vmlinuz-5.15.55 root=/dev/sda2 quiet single
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}
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# Memory test entry
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menuentry "MemTest86+ 4.20" {
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linux16 (hd0,msdos2)/boot/memtest86+-4.20.bin
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}
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@]
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Save the manual configuration file as '''/boot/grub/grub.cfg'''.
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[[#syslinux-install]]
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!! SYSLINUX installation notes
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The venerable bootloader LILO has been dropped as of CRUX version 3.7; most
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users will find it straightforward to adopt GRUB instead. This section presents
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another option, the SYSLINUX bootloader.
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!!! Precaution
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Installing a new boot manager is like modifying the partition table using fdisk
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or installing a new system kernel. Please create a rescue boot disk first!
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!!! Installation -- UEFI booting
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If your motherboard supports the UEFI boot mode, then installation of syslinux
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is as simple as copying a few files to the EFI system partition (mounted at
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%fn%/boot/efi%% in the example commands below) and writing a configuration that
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tells syslinux where to find your kernel. First confirm that EFI variables are
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visible to the currently-running kernel; if you run @@efivar -l@@ and see a list
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of %fn%universally-unique-identifier-VariableName%%s, then the following
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commands should be sufficient.
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$ mkdir -p /boot/efi/BOOT
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$ cd /boot/efi/BOOT
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$ cp /usr/share/syslinux/efi64/ldlinux.e64 .
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$ cp /usr/share/syslinux/efi64/syslinux.efi BOOTX64.EFI
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$ cp /usr/src/linux-5.15.55/arch/x86/boot/bzImage vmlinuz-5.15.55
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$ vi syslinux.cfg
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-> Remember to change %fn%/boot/efi%% to the actual mount point of your EFI
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system partition.
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-> Observe that the EFI bootloader was given a generic name in the fourth line
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above. If you had saved it in fn%/boot/efi/BOOT%% using the original filename
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provided by the '''syslinux''' package, then it would have been necessary to run
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@@efibootmgr@@ to inform the BIOS about this new bootloader-like object. See
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[[#EFI-stub-install | "EFI Stub installation"]] for an example of using
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@@efibootmgr@@ to create new boot entries.
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-> The fifth command puts a copy of the kernel (renamed to show version
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information) in the working directory. The final command starts the vi editor on
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a buffer that will be written to %fn%syslinux.cfg%%, which must contain a line
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giving the path to the kernel image. See the [[#syslinux-cfg| "SYSLINUX
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configuration file template"]] for details.
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!!! Installation -- Legacy (MBR) booting
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If your motherboard does not support UEFI boot mode (or if you disabled it
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deliberately), then installing syslinux will require you to overwrite the master
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boot record (MBR). The '''syslinux''' package provides two different binary
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blobs that can occupy the designated MBR area of the hard disk. To determine
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which binary blob is appropriate, you will need to remember what kind of
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partition table you wrote when you initialized your disk for CRUX. The older DOS
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(MBR) partition table is supported by %fn%/usr/share/syslinux/mbr.bin%%, while
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the newer GPT (GUID) partition table is supported by
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%fn%/usr/share/syslinux/gptmbr.bin%%. You can run @@fdisk -l /dev/sda@@
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(replacing ''sda'' with your actual device) to remind yourself what the existing
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partition table looks like. An identification of the exact partition type (DOS
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or GPT) will appear next to ''Disklabel type:'' in the fdisk output.
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Once you determine the binary blob that will work with your partition table, run
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the commands that will copy that binary blob into the master boot record.
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'''Remember to replace ''sda'' with your actual device. The first command sets
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''INSTALLDIR'' as the path to a directory on a vfat or ext2/3/4 filesystem
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('''which must be flagged as bootable in the partition table'''). In this
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example we use a path that minimizes the hassle when toggling your BIOS between
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UEFI and legacy boot methods. A less confusing option is commented out, for
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BIOSes that truly have no UEFI capability.'''
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$ INSTALLDIR=/boot/efi/EFI/BOOT # or /boot/syslinux
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$ PTYPE=$(fdisk -l /dev/sda | grep "^Disklabel type" | cut -d " " -f3)
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$ [ "$PTYPE" = "gpt" ] && BINBLOB=gptmbr.bin || BINBLOB=mbr.bin
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$ mkdir -p $INSTALLDIR
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$ cd $INSTALLDIR
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$ cp /usr/share/syslinux/ldlinux.c32 .
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$ extlinux --install $INSTALLDIR
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$ dd bs=440 count=1 conv=notrunc if=/usr/share/syslinux/$BINBLOB of=/dev/sda
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$ vi syslinux.cfg
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-> The @@extlinux@@ command takes a ''directory under a mounted partition'' as
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its argument, rather than a device node. Upstream documentation begins with an
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example of calling the @@syslinux@@ command with the ''device node'' as its
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argument, which assumes that the partition is not mounted. Because you're
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already creating files on this partition, we demonstrate the command that won't
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require you to unmount the partition before running it.
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The @@extlinux@@ command is also smart enough to set its argument (the ''install
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target'') as the directory to be searched for configuration files, so you can
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proceed to launch the editor on %fn%syslinux.cfg%% (see the next section for a
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template) without changing directory.
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[[#syslinux-cfg]]
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!!! Template for a SYSLINUX configuration file
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Now that the SYSLINUX bootloader is successfully installed, you need to tell it
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where to find your kernel and the root filesystem.
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[@
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default CRUX-3.7
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prompt 1
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timeout 10
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label CRUX-3.7
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say "Now booting into CRUX"
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kernel vmlinuz-5.15.55
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append root=/dev/sda2 rw quiet
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@]
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When giving the location of a kernel image, relative paths are interpreted in
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reference to the %fn%syslinux.cfg%% file. In the example above, if
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@@extlinux@@ assigned %fn%/boot/efi/EFI/BOOT/%% as the preferred location for
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%fn%syslinux.cfg%%, the kernel would have to be copied to
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%fn%/boot/efi/EFI/BOOT/vmlinuz-5.15.55%%.
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[[#EFI-stub-install]]
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!! EFI Stub installation notes
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GRUB and SYSLINUX offer the most familiar experience for users coming from LILO.
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After a one-time interaction with the BIOS and the Master Boot Record, all
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subsequent updates to the GRUB or SYSLINUX configuration only involve editing a
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flat-text file. Although with LILO you had to run @@/sbin/lilo@@ after editing
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its flat-text config, for GRUB and SYSLINUX you never have to touch the contents
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of the bootsector or the NVRAM after the initial installation; changes to their
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flat-text config files are automatically detected.
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A third way to boot into your CRUX system involves direct interaction with the EFI
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variables, letting the Linux kernel image provide the required EFI bootloader
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code. This option has a workflow that might remind you of running @@/sbin/lilo@@
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after building and installing each new kernel.
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-> Note: this type of booting only works in UEFI mode, and when your kernel has
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been built with ''CONFIG_EFI_STUB=y''. Legacy MBR booting is not supported with
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this method.
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As with GRUB and SYSLINUX, the kernel has to be told which device to use as a
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root filesystem. Most modern BIOSes allow you to append options like
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''root=/dev/sda2'' to the line that boots the kernel, but some buggy UEFI
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implementations do not honor such appended options. To be safe, you can
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customize the boot options during the kernel configuration process (the
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@@make menuconfig@@ step), at the expense of making it harder to put the disk in
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an external enclosure and boot from USB (when you want to travel lightly). If
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you leave the boot options empty during kernel configuration, and the BIOS does
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not honor your appended options, you might have to boot from a rescue disk to
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get back into your system and fix things.
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* Copy your built kernel to a subdirectory of the EFI system partition
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(mounted at %fn%/boot/efi%%). For maximum compatibility, save it with the
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extension %fn%.efi%%.
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[@
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$ mkdir -p /boot/efi/BOOT
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$ cd /boot/efi/BOOT
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$ cp /usr/src/linux-5.15.55/arch/x86/boot/bzImage vmlinuz-5.15.55.efi
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@]
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* Next, create a boot entry telling the BIOS about the kernel image you just saved.
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$ efibootmgr -c -d /dev/sda -L 'Linux 5.15.55' -l '\BOOT\vmlinuz-5.15.55.efi' -u 'root=/dev/sda2'
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-> For maximum portability, you can also identify the root filesystem using its
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partition UUID. Run @@ls -l /dev/disk/by-partuuid/@@ to discover the UUID of the
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known partitions, and then modify the @@efibootmgr@@ arguments to use the
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identifier of the root partition. '''Note: this option is more fragile than
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specifying the root partition using its device node, because of the delay in
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scanning all partitions to construct the list of their UUIDs. If you encounter
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an error when booting your CRUX system this way, you will have to use the
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installation media (or another rescue disk) to recreate the EFI boot entry with
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device node instead, or with an additional boot option that gives the kernel more
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time to enumerate the partitions.'''
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$ efibootmgr -c -d /dev/sda -L 'Linux 5.15.55' -l '\BOOT\vmlinuz-5.15.55.efi' -u 'root=PARTUUID=c3259ad5-...'
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* Finally, change the boot order so that the newly-created boot entry is the
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first one tried. Start by finding the number assigned to the newly-created
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entry, and then use that number to specify the desired boot order. EXAMPLE:
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[@
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$ efibootmgr
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BootCurrent: 0000
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Timeout: 1 seconds
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BootOrder: 0000,0001
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Boot0000* Linux 5.15.26 HD(1,GPT,d5a44413-...,0x800,0x64000)/File(\BOOT\vmlinuz-5.15.26.efi)72006f006f0074...
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Boot0001* Linux 5.15.55 HD(1,GPT,d5a44413-...,0x800,0x64000)/File(\BOOT\vmlinuz-5.15.55.efi)72006f006f0074...
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$ efibootmgr -o 0001,0000
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@]
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[[#initramfs]]
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!! Notes on Initramfs
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A common scenario that prevents the usual practice of booting a slimmed-down
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kernel containing only the drivers for the root filesystem (and then loading
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modules to initialize other hardware) is that the root filesystem is not a
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physical volume, but rather a logical volume inside an encryption layer like
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LUKS. To handle this situation, you will need to go beyond the kernel building
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process outlined above, and also create a compressed filesystem image (called an
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''initramfs'') that contains the lvm2 and cryptsetup packages (and the drivers
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for usb input devices, if you chose not to compile them into the kernel).
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Creating such an initramfs was once an intricate procedure, but tools like
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'''dracut''' make it much simpler these days.
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If running @@dracut@@, and saving the initramfs alongside the kernel in the EFI
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system partition, had been the only deviations from the usual CRUX installation
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procedure, then one section of the appendix would suffice to explain how to do
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full-disk encryption in CRUX. But preparation for this setup begins at the
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partitioning stage, when you need to call commands from the '''lvm2''' and
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'''cryptsetup''' packages before creating and mounting your filesystems. So this
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section of the appendix just points to a separate document, where an
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[[CRUX-3.7-Encrypted.txt | outline for installing CRUX with full-disk encryption]]
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is given from beginning to end. Even if full-disk encryption is not your desired
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endpoint and you just want to learn more about highly-modular kernel configs,
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the need for an initramfs is easier to motivate by considering a specific use
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case like full-disk encryption. Studying the upstream documentation for any
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unfamiliar command in the linked outline (eg., %fn%cryptsetup%%, %fn%pvcreate%%,
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or %fn%dracut%%) is an excellent way to distinguish the functions performed by
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the various components.
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