= Using the GRUB2 boot prompt
[[using-the-grub-2-boot-prompt]]

If improperly configured, *GRUB2* may fail to load and subsequently drop
to a boot prompt. To boot into the system, follow the steps below.

.Procedure

. Load the necessary modules to read your system's partitions (you will also need to load `part_msdos` or `part_gpt`, depending on your partition table).
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* For BTRFS filesystems (Fedora 33 or newer).
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grub> insmod btrfs
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* For LVM filesystems (older than Fedora 33).
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grub> insmod xfs
grub> insmod lvm
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. List the drives which *GRUB2* sees.
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grub> ls
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. Examine the output to understand the partition table of the `/dev/sda` device. The following example shows a DOS partition table with three partitions.
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(hd0) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1)
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A GPT partition table of the `/dev/sda` device with four partitions could look like this.
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(hd0) (hd0,gpt4) (hd0,gpt3)  (hd0,gpt2) (hd0,gpt1)
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. Probe each partition of the drive and locate your `vmlinuz` and `initramfs` files.
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grub> ls (hd0,1)/
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The outcome of the previous command will list the files on `/dev/sda1`. The partition that contains the `/boot` directory is the correct one. There you will search for the full names of the `vmlinuz` and `initramfs` files.

. Follow the <<btrfs-boot-setup, Pre-boot setup for BTRFS>> or the <<lvm-boot-setup, Pre-boot setup for LVM>> to recover your system.

. After the pre-boot setup, boot the system.
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grub> boot
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. To restore the bootloader's functionality, regenerate the *GRUB2* configuration file and reinstall the bootloader, as described in xref:adding-other-operating-systems-grub2[Adding other operating systems to the *GRUB2* menu].

[[btrfs-boot-setup]]
== Pre-boot setup for BTRFS filesystems.

* On BIOS systems.

. Set *GRUB2* root to your `/boot` partition. If your `/boot` partition is `(hd0,msdos1)`, the command will be.
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grub> set root=(hd0,msdos1)
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. Next, select the desired kernel. Set the `/root` partition (e.g. `/dev/sda2`).
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grub> linux /vmlinuz-5.14.10-300.fc35.x86_64 root=/dev/sda2 ro rootflags=subvol=root
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* On UEFI systems.

. Set *GRUB2* root to your EFI system partition. If your EFI system partition is `(hd0,gpt1)`, use this command.
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grub> set root=(hd0,gpt1)
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. Next, select the desired kernel. Find the path to `vmlinuz` and set the `/root` partition (e.g. `/dev/sda3`).
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grub> linux (hd0,gpt2)/vmlinuz-5.14.10-300.fc35.x86_64 root=/dev/sda3 ro rootflags=subvol=root
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. Select the RAM filesystem that will be loaded.
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grub> initrd (hd0,gpt2)/initramfs-5.14.10-300.fc35.x86_64.img
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[[lvm-boot-setup]]
== Pre-boot setup for LVM filesystems.

* On BIOS systems.

. Set *GRUB2* root to your `/boot` partition. If your `/boot` partition is `(hd0,msdos1)`, use this command.
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grub> set root=(hd0,msdos1)
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. Next, select the desired kernel. Set `root` to the logical volume that corresponds to the `/root` directory.
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grub> linux /vmlinuz-3.0.0-1.fc16.i686 root=/dev/mapper/fedora_localhost--live-root
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. Select the RAM filesystem that will be loaded.
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grub> initrd /initramfs-3.0.0-1.fc16.i686.img
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* On UEFI systems.

. Set *GRUB2* root to your EFI system partition. If your EFI system partition is `(hd0,gpt1)`, use this command.
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set root=(hd0,gpt1)
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. Next, select the desired kernel. Find the path to `vmlinuz` and set `root` to the logical volume that corresponds to the `/root` directory.
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linux (hd0,gpt2)/vmlinuz-3.0.0-1.fc16.i686 root=/dev/mapper/fedora_localhost--live-root
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. Select the RAM filesystem that will be loaded.
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initrd (hd0,gpt2)/initramfs-3.0.0-1.fc16.i686.img
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