I want to hack around with booting from removable media, but ran into some problems. On one laptop, an HP Notebook - 17-by0062st, I am unable to get grub to even recognize a USB stick present in a default boot. That is to say, I let the machine boot normally from the internal hard drive and press 'c' before grub times out to enter the console. I type
ls at the grub terminal and see
grub> ls (hd0) (hd0,gpt4) (hd0,gpt3) (hd0,gpt2) (hd0,gpt1) (cd0)
The hd0 item with 4 GPT partitions is the internal HDD and is always viewable. I am assuming the cd0 item is my optical drive. It always shows up in the output of
ls, although no disk is in the drive. When I boot with a USB stick in a USB port, there is no additional item as I would expect. The orange light in the USB stick is on, so the motherboard has found it. The USB stick is in a valid state. I can mount it and view the files once I am in my ordinary GNU operating system. Additionally, on a different laptop (a Dell Latitude), the output of
ls included entries for
(hd1) (hd1,msdos1) and I was able to list the files with
ls (hd1,msdos1)/ as expected.
This is an EFI laptop. The old Dell Latitude (that worked) is BIOS. Other than that, I don't know of anything else. Is there an obvious module I can import or a command I can run to get grub to probe for drives again, or something like that?
So the plot has thickened. When I let the laptop boot normally directly into grub, the USB does not show up as described, however, if I press
ESC as it powers on and go into the EFI boot menu and manually select grub, a USB device will be visible. I have verified this for two flash sticks and a WD My Book external HDD. It is almost like when you let it do the default boot sequence it is too fast or something like that, but everything is properly mapped if you go through the boot menu and grub understands where the drive is.
I'll leave this for another day or so in case anyone knows anything about this, but it may be a question I have to send specifically to the grub developers.