146 lines
6.5 KiB
Plaintext
146 lines
6.5 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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[[#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/EFI/BOOT
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$ cd /boot/efi/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 '\EFI\BOOT\vmlinuz-5.15.55.efi' -u 'root=/dev/sda2'
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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(\EFI\BOOT\vmlinuz-5.15.26.efi)72006f006f0074...
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Boot0001* Linux 5.15.55 HD(1,GPT,d5a44413-...,0x800,0x64000)/File(\EFI\BOOT\vmlinuz-5.15.55.efi)72006f006f0074...
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$ efibootmgr -o 0001,0000
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@]
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-> As in the UEFI installation of SYSLINUX, the subdirectory %fn%EFI/BOOT%%
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of the EFI system partition is the default path where the BIOS expects to
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find a bootloader. This location is more obvious in the @@efibootmgr@@
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commands, since @@efibootmgr@@ is agnostic about the mountpoint of your
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EFI system partition. The two most common ways to shorten what looks like an
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overly-verbose path to the kernel are:
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** mount your EFI system partition somewhere else (and adjust the @@mkdir@@ and @@cd@@ commands as needed).
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** save your kernel closer to the root of the EFI system partition (and change the @@efibootmgr@@ invocation as needed).
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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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