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content/2015/02/25/single-uefi-executable-for-kernelinitrdcmdline.md

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+title = "Single UEFI executable for kernel+initrd+cmdline"
+date = 2015-02-25T15:55:16+00:00
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+
+Lately Kay Sievers and David Herrmann created a UEFI
+[loader stub](http://cgit.freedesktop.org/gummiboot/tree/src/efi/stub.c), which starts a linux kernel
+with an initrd and a kernel command line, which are COFF sections of the executable.
+This enables us to create single UEFI executable with a standard distribution kernel,
+a custom initrd and our own kernel command line attached.
+
+<!-- more -->
+
+Of course booting a linux kernel 
+directly from the UEFI has been possible before with the kernel EFI stub. But to add an initrd and 
+kernel command line, this had to be specified at kernel compile time.
+
+To demonstrate this feature 
+and have a useful product, I created a shell script, which creates a "rescue" image on Fedora with 
+the rescue kernel and rescue initrd. The kernel command line "rd.auto" instructs dracut to assemble 
+all devices, while waiting 20 seconds for device appearance "rd.retry=20" and drop to a final shell 
+because "root=/dev/failme" is specified (which does not exist of course). Now in this shell you can 
+fsck your devices, mount them and repair your system.
+
+The shell script can be downloaded and viewed on 
+[github](https://github.com/haraldh/mkrescue-uefi).
+
+To run the script, you will need to install gummiboot >= 46 and binutils. 
+```console
+# yum install gummiboot binutils
+```
+
+Run the script: 
+```console
+# bash mkrescue-uefi.sh BOOTX64.EFI
+```
+ 
+Copy `BOOTX64.EFI` to e.g. a USB stick to `EFI/BOOT/BOOTX64.EFI` in the FAT boot partition 
+and point your BIOS to boot from the USB stick. Voilà!
+
+A rescue USB stick with just one file! :-)