jcktrue.dk/content/post/grub-trampoline/index.md

---
title: "GRUB Trampoline"
subtitle: "Install GRUB on a spare drive"
summary: "Using a spare drive to act as a trampoline during the boot process."
date: 2021-05-03T15:28:14+02:00
highlight: true
---
# Background

Due to a BIOS bug in my HP MicroServer I have been forced to applied a workaround. 

The MicroServer Gen8 has a bug that prevents the use of the 5th SATA port as the primary boot device. It will automatically attempt to boot from SATA port 1 if a drive is inserted, then port 2 and so forth. By removing all the fixed drives it is possible to make the system boot from port 5.

It is however possible to boot from the internal USB port or the internal MicroSD slot by default. So to solve this issue we are going to install GRUB onto a spare MicroSD card or a USB stick. The size or quality of the drive should not matter since it is only needed for GRUB to jump to the drive present on the 5th SATA port.

# Steps
## Format the USB/SD Card
First we need to correctly format the new disk as a bootable FAT drive.

{{% callout warning %}}
Be very cautious when formatting storage drives. Executing a command on the wrong drive could have disastrous consequences.
{{% /callout %}}

Find the correct device identifier.


```shell
lsblk
```

Clear the drive by writing all zeros to the drive (for good measure)

```shell
sudo dd if=/dev/zero of=/dev/sdX
```

Format the disk

```shell
sudo fdisk /dev/sdX
```

Fdisk provides a shell where you can enter commands.
- Set the type to "o" for MSDOS
- Set the disk to be bootable "a"
- Make a new primary partition "n" followed by "n" Accept the remaining as default.
- Use "w" to commit the changes and exit the tool.

Now create a filesystem in the newly created partition.

```shell
sudo mkfs -t ext2 /dev/sdX1
```

## Prepare for GRUB install
Create a mount point

```shell
mkdir /tmp/mysub
```

Mount the new partition

```shell
sudo mount /dev/sdX1 /tmp/myusb
```

Create a folder named "boot" on the drive

```shell
sudo mkdir /tmp/myusb/boot
```

## Install GRUB
Install GRUB by running the grub-install script

```shell
sudo grub-install --boot-directory=/tmp/myusb/boot /dev/sdX
```

Update the GRUB configuration

```shell
sudo update-grub --output=/tmp/myusb/boot/grub/grub.cfg
```

## Test
Finally unmount and reboot 
```shell
sudo unmount /tmp/myusb
sudo reboot
```