[2024-feb-29] Sad news: Eric Layton aka Nocturnal Slacker aka vtel57 passed away on Feb 26th, shortly after hospitalization. He was one of our Wiki's most prominent admins. He will be missed.

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howtos:slackware_admin:linux_kernel_options_for_uefi_and_elilo [2014/02/07 01:37 (UTC)] – Added external links section metaschimahowtos:slackware_admin:linux_kernel_options_for_uefi_and_elilo [2021/01/11 07:07 (UTC)] (current) – fix for mmcblk louigi600
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       * EFI Variable Support via sysfs (CONFIG_EFI_VARS [=n])       * EFI Variable Support via sysfs (CONFIG_EFI_VARS [=n])
 as it is deprecated in favor of CONFIG_EFIVAR_FS, because it has a 1024-byte variable size limit, and because it can [[https://lkml.org/lkml/2013/4/16/473|cause data inconsistency issues]]. as it is deprecated in favor of CONFIG_EFIVAR_FS, because it has a 1024-byte variable size limit, and because it can [[https://lkml.org/lkml/2013/4/16/473|cause data inconsistency issues]].
-However, if you do disable this, you will need a fork of the ''efibootmgr'' program that supports the new EFI Variable filesystem found at: +However, if you do disable this, you will need a fork of the ''efibootmgr'' program that supports the new EFI Variable filesystem.
-https://github.com/vathpela/efibootmgr/tree/libefivars+
 </note> </note>
 +==== Using the new EFI variable filesystem ====
 +In order to use the new EFI variable filesystem interface, you need to remove the old ''efibootmgr'' program and replace it with a new one that supports the EFI variable filesystem.
 +  - Download and install: https://github.com/vathpela/efivar
 +  - Download and install: https://github.com/rhboot/efibootmgr
 +  - Run:<code>
 +modprobe efivarfs
 +mount -t efivarfs efivarfs /sys/firmware/efi/efivars
 +efibootmgr
 +</code>
 ==== The EFI System Partition (ESP) ==== ==== The EFI System Partition (ESP) ====
 In order to boot from UEFI you need to create an EFI System Partition (ESP) using ''gdisk'' or ''cgdisk'' instead of the old ''fdisk'' and ''cfdisk''. The Slackware [[ftp://mirrors.usc.edu/pub/linux/distributions/slackware/slackware64-14.1/README_UEFI.TXT|README_UEFI.TXT]] recommends a size of 100M, which is also the minimum partition size (except for 4K native drives, where it is 260M). You also need to set the partition hex code to ''EF00'', which identifies it as the ESP. In order to boot from UEFI you need to create an EFI System Partition (ESP) using ''gdisk'' or ''cgdisk'' instead of the old ''fdisk'' and ''cfdisk''. The Slackware [[ftp://mirrors.usc.edu/pub/linux/distributions/slackware/slackware64-14.1/README_UEFI.TXT|README_UEFI.TXT]] recommends a size of 100M, which is also the minimum partition size (except for 4K native drives, where it is 260M). You also need to set the partition hex code to ''EF00'', which identifies it as the ESP.
 ==== UEFI and ELILO ==== ==== UEFI and ELILO ====
-During the install procedure of Slackware 14.1 for ELILO (the ''eliloconfig'' script), the following happens and is required for booting from UEFI using ELILO.+During the install procedure of Slackware 14.1 or above for ELILO (the ''eliloconfig'' script), the following happens and is required for booting from UEFI using ELILO.
  
   - The EFI System Partition (ESP) is located and mounted. On a running system it is usually found already mounted at ''/boot/efi''. This is a special FAT partition that is basically the UEFI firmware replacement of what the MBR was for BIOS. However, it can not only hold a bootloader (all the MBR was capable of), but also config files, the kernel, and other things you might want to access using the UEFI firmware.   - The EFI System Partition (ESP) is located and mounted. On a running system it is usually found already mounted at ''/boot/efi''. This is a special FAT partition that is basically the UEFI firmware replacement of what the MBR was for BIOS. However, it can not only hold a bootloader (all the MBR was capable of), but also config files, the kernel, and other things you might want to access using the UEFI firmware.
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     - The kernel, usually titled ''vmlinuz''     - The kernel, usually titled ''vmlinuz''
   - A boot entry variable is registered in the UEFI firmware using ''efibootmgr''. The exact command that is run is <code bash>   - A boot entry variable is registered in the UEFI firmware using ''efibootmgr''. The exact command that is run is <code bash>
-EFI_DEVICE=$(mount | grep vfat | grep -w /boot/efi | cut -b 1-8) +EFIDISK=$(df  /boot/efi/ |awk 'END{printf("%s\n",$1)}') 
-EFI_PARTITION=$(mount | grep vfat | grep -w /boot/efi | cut -f 1 -d ' ' | cut -b 9-)+EFI_DEVICE=$(sed 's%[0-9]\+$%%;s%\([0-9]\)p%\1%' <<< $EFIDISK) 
 +EFI_PARTITION=$(sed 's%.*[a-z]\([0-9]\+\)$%\1%' <<< $EFIDISK)
 efibootmgr -q -c -d $EFI_DEVICE -p $EFI_PARTITION -l "\\EFI\\Slackware\\elilo.efi" -L "Slackware" efibootmgr -q -c -d $EFI_DEVICE -p $EFI_PARTITION -l "\\EFI\\Slackware\\elilo.efi" -L "Slackware"
 </code> so if ''mount'' outputs <code>/dev/sda1 on /boot/efi type vfat (rw)</code>EFI_DEVICE would be ''/dev/sda'' and EFI_PARTITION would be ''1'', each components of ''/dev/sda1'', which is the ESP. </code> so if ''mount'' outputs <code>/dev/sda1 on /boot/efi type vfat (rw)</code>EFI_DEVICE would be ''/dev/sda'' and EFI_PARTITION would be ''1'', each components of ''/dev/sda1'', which is the ESP.
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 ==== Updating your UEFI firmware ==== ==== Updating your UEFI firmware ====
 As all UEFI firmware has a flashing utility built-in, it is now much easier to update the firmware. All you have to do is copy the new firmware onto the ESP and the UEFI firmware should recognize it when you go to the flashing utility menu. However, remember that flashing the firmware can still potentially brick the system, especially if it is interrupted during the flashing process. As all UEFI firmware has a flashing utility built-in, it is now much easier to update the firmware. All you have to do is copy the new firmware onto the ESP and the UEFI firmware should recognize it when you go to the flashing utility menu. However, remember that flashing the firmware can still potentially brick the system, especially if it is interrupted during the flashing process.
 +<note important>
 +Updating your UEFI firmware may reset your settings and prevent you from booting unless you plan ahead.
 +</note>
 +==== My UEFI settings were reset and I can't boot, or planning ahead to avoid surprises ====
 +This can happen either after updating the UEFI firmware or after replacing the CMOS battery. There are three main ways to fix it:
 +  - Probably the easiest and most convenient way is to use the default boot location. Note that some UEFI firmwares do NOT support the default boot location, so this will not work. However, if it does, you won't have to worry about the system not booting again. To do this you can boot into the Slackware install DVD, mount the ESP and copy the files to the following places:
 +    - ''elilo.efi'' -> ''/EFI/boot/bootx64.efi''
 +    - ''elilo.conf'' -> ''/EFI/boot/elilo.conf''
 +    - ''vmlinuz'' -> ''/EFI/boot/vmlinuz''
 +  - You can boot into the Slackware install DVD, run through the menus, and reinstall elilo.
 +  - You can download and install one of the following EFI shells to the root directory of your ESP (that is ''/'' NOT ''/EFI'').
 +    - [[https://svn.code.sf.net/p/edk2/code/trunk/edk2/ShellBinPkg/UefiShell/X64/Shell.efi|This version supports only UEFI version 2 and up]]
 +    - [[http://dl.dropbox.com/u/17629062/Shell2.zip | This version may support earlier UEFI versions]]
 +    - Boot into the shell and run: <code>bcfg boot add 0 fs0:\EFI\Slackware\elilo.efi Slackware</code>
 ==== External Links ==== ==== External Links ====
 [[http://blog.uncooperative.org/blog/2014/02/06/the-efi-system-partition/|A comprehensive analysis of the ESP and default boot behavior.]] [[http://blog.uncooperative.org/blog/2014/02/06/the-efi-system-partition/|A comprehensive analysis of the ESP and default boot behavior.]]

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