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---
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lang: en
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layout: doc
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permalink: /doc/uefi-troubleshooting/
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ref: 177
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title: UEFI Troubleshooting
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---
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## Successfully installed in legacy mode, but had to change some xen parameters
**Note**: If you make changes, you must boot from "Partition 1" explicitly from UEFI boot menu.
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**Change the xen configuration on a USB media**
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01. Attach the usb disk, mount the EFI partition (second partition available on the disk)
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02. Open a terminal and enter the command `sudo su -` . Use your preferred text editor (e.g `vi` ) to edit your xen config (`EFI/BOOT/grub.cfg` ):
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```
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vi EFI/BOOT/grub.cfg
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```
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03. Change the `multiboot2 /images/pxeboot/xen.gz` line to add your xen parameters on the boot entry of your choice
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04. Install using your modified boot entry
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**Change xen configuration directly in an iso image**
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01. Set up a loop device (replacing `X` with your ISO's version name): `losetup -P /dev/loop0 Qubes-RX-x86_64.iso`
02. Mount the loop device: `sudo mount /dev/loop0p2 /mnt`
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03. Edit `EFI/BOOT/grub.cfg` to add your params to the `multiboot2 /images/pxeboot/xen.gz` line
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04. Save your changes, unmount and dd to usb device
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## Installation freezes before displaying installer
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If you have an Nvidia card, see [Nvidia Troubleshooting ](https://github.com/Qubes-Community/Contents/blob/master/docs/troubleshooting/nvidia-troubleshooting.md#disabling-nouveau ).
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## Installation from USB stick hangs on black screen
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Some laptops cannot read from an external boot device larger than 8GB. If you encounter a black screen when performing an installation from a USB stick, ensure you are using a USB drive less than 8GB, or a partition on that USB lesser than 8GB and of format FAT32.
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## Installation completes successfully but then system crash/restarts on next boot
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Some Dell systems and probably others have [another bug in UEFI firmware ](http://markmail.org/message/amw5336otwhdxi76 ).
These systems need `efi=attr=uc` enabled at all times.
Although this is enabled by default in the installer, it is disabled after the first stage of a successful install.
You can re-enable it either as part of the install process:
1. Perform installation normally, but don't reboot the system at the end yet.
2. Go to `tty2` (Ctrl-Alt-F2).
3. Execute:
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```
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sed -i -e 's/ucode=scan/\0 efi=attr=uc/' /mnt/sysimage/boot/efi/EFI/qubes/grub.cfg
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```
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4. Go back to `tty6` (Ctrl-Alt-F6) and click `Reboot` .
5. Continue with setting up default templates and logging in to Qubes.
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Or if you have already rebooted after the first stage install and have encountered this issue, by:
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1. Boot Qubes OS install media into [rescue mode ](/doc/uefi-troubleshooting/#accessing-installer-rescue-mode-on-uefi )
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2. Press '3' to go to the shell
3. Find and mount the EFI system partition. (replace `/dev/sda` with your disk name. If unsure, use the `lsblk` command to display a list of disks):
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```
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fdisk -l /dev/sda | grep EFI
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```
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The output should look like this:
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```
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/dev/sda1 2048 1230847 1228800 600M EFI System
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```
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Then mount it:
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```
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mkdir -p /mnt/sysimage/boot/efi
mount /dev/sda1 /mnt/sysimage/boot/efi
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```
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4. Execute:
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```
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sed -i -e 's/ucode=scan/\0 efi=attr=uc/' /mnt/sysimage/boot/efi/EFI/qubes/grub.cfg
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```
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5. Type `reboot` .
6. Continue with setting up default templates and logging in to Qubes.
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## Boot device not recognized after installing
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Some firmware will not recognize the default Qubes EFI configuration.
As such, it will have to be manually edited to be bootable.
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1. Boot Qubes OS install media into [rescue mode ](/doc/uefi-troubleshooting/#accessing-installer-rescue-mode-on-uefi )
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2. Press '3' to go to the shell
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3. Find and mount the EFI system partition. (replace `/dev/sda` with your disk name. If unsure, use the `lsblk` command to display a list of disks):
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```
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fdisk -l /dev/sda | grep EFI
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```
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The output should look like this:
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```
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/dev/sda1 2048 1230847 1228800 600M EFI System
```
Then mount it:
```
mkdir -p /mnt/sysimage/boot/efi
mount /dev/sda1 /mnt/sysimage/boot/efi
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```
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4. Copy `grubx64.efi` to the fallback path:
```
cp /mnt/sysimage/boot/efi/EFI/qubes/grubx64.efi /mnt/sysimage/boot/efi/EFI/BOOT/bootx64.efi
```
5. Type `reboot`
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## "Qubes" boot option is missing after removing / attaching a disk or updating the BIOS
1. Boot Qubes OS install media into [rescue mode ](/doc/uefi-troubleshooting/#accessing-installer-rescue-mode-on-uefi )
2. Press '3' to go to the shell
3. Create boot entry in EFI firmware (replace `/dev/sda` with your disk name and `-p 1` with `/boot/efi` partition number):
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```
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efibootmgr -v -c -u -L Qubes -l /EFI/qubes/grubx64.efi -d /dev/sda -p 1
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```
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## Accessing installer Rescue mode on UEFI
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Choose "Rescue a Qubes OS system" from grub2 boot menu.