grub

4 Articles

Bits of GRUB syntax on pink background

Wake, Boot, Repeat: Remote OS Selection With GRUB And ESP

March 3, 2025 by 14 Comments

What do you do when you need to choose an OS at boot but aren’t physically near your machine? [Dakhnod]’s inventive solution is a mix of GRUB, Wake-on-LAN (WOL), and a lightweight ESP8266 running a simple HTTP server. In the past, [dakhnod] already enlightened us with another smart ESP hack. This one’s a clever combination of network booting and remote control that opens up possibilities beyond the usual dual-boot selector.

At its core, the hack modifies GRUB to fetch its boot configuration over HTTP. The ESP8266 (or any low-power device) serves up a config file defining which OS should launch. The trick lies in adding a custom script that tells GRUB to source an external config:

#!/usr/bin/env cat 
net_dhcp 
source (http,destination_ip_or_host:destination_port)/grub/config

Since GRUB itself makes the HTTP request, the system needs a running web server. That could be a Raspberry Pi, another machine, or the ESP itself. From there, a WOL-enabled ESP button can wake the PC and set the boot parameters remotely.

Is it secure? Well, that depends on your network. An open, unauthenticated web server dishing out GRUB configs is risky, but within a controlled LAN or a VLAN-segmented environment, it’s an intriguing option. Automation possibilities are everywhere — imagine remotely booting test rigs, toggling between OS environments for debugging, or even setting up kiosk machines that reconfigure themselves based on external triggers.

For those looking to take it further, using configfile instead of source allows for more dynamic menu entries, although it won’t persist environment variables. You could even combine it with this RasPi hack to control the uptime of the HTTP server. The balance between convenience and security is yours to strike.

If you’ve got your own wild GRUB customisation, let’s hear it!

An Old Netbook Spills Its Secrets

March 27, 2023 by 35 Comments

For a brief moment in the late ’00s, netbooks dominated the low-cost mobile computing market. These were small, low-cost, low-power laptops, some tiny enough to only have a seven-inch display, and usually with extremely limiting hardware even for the time. There aren’t very many reasons to own a machine of this era today, since even the cheapest of tablets or Chromebooks are typically far more capable than the Atom-based devices from over a decade ago. There is one set of these netbooks from that time with a secret up its sleeve, though: Phoenix Hyperspace.

Hyperspace was envisioned as a way for these slow, low-power computers to instantly boot or switch between operating systems. [cathoderaydude] wanted to figure out what made this piece of software tick, so he grabbed one of the only netbooks that it was ever installed on, a Samsung N210. The machine has both Windows 7 and a custom Linux distribution installed on it, and with Hyperspace it’s possible to switch almost seamlessly between them in about six seconds; effectively instantly for the time. Continue reading “An Old Netbook Spills Its Secrets” →

The TinyPICO board and the rocker switch soldered together showing a complete device, shown being held in the air by a crocodile clip

Simple Hardware Switch For OS Dualbooting, Thanks To RP2040

May 2, 2022 by 43 Comments

Dualbooting your computer can be a chore, the more switching between OSes you have to do – which is why virtualization or having separate computers are the go-to for many. Failing that, we have no choice but to smooth over our dualbooting experience with various workarounds and helpers. [William Somsky] shares one such helper tool with us – an elegant device made with a RP2040-sporting TinyPICO board and a three-way rocker switch, directing GRUB to boot into either Windows or Linux automatically, or leave us with the usual boot menu. This way, you can just flip the switch, hit “reboot” and walk away, coming back to your PC booted into OS of your choice, instead of timing your presence just so that you can catch the boot menu on time.

All you need to do is to solder a rocker switch to your RP2040 board of choice, then flash the RP2040 with code that detects the state of the switch, and creates a mass storage device hosting a file setting a Grub variable to either one of the 0, 1 or 2. [William] describes his journey, fighting mysterious caching problems, but tells us he got it working in the end. Sadly, [William] hasn’t shared the RP2040-side code with us, but he has at least put the Grub’s custom.cfg file in the ‘Files’ section of the Hackaday.io project.

Readily accessible microcontrollers with mass storage functions sure help make such hacks simple – earlier, we’ve seen dualboot switching like this done by modifying assembly code of the MBR. Dualbooting is a hacker’s rite of passage, and certain OSes of late can make it harder than other ones. Even if you don’t want to dualboot your PC, however, you sure can dualboot an Arduino!

Tales From The Sysadmin: Dumped Into The Grub Command Line

November 25, 2019 by 53 Comments

Today I have a tale of mystery, of horror, and of hope. The allure of a newer kernel and packages was too much to resist, so I found myself upgrading to Fedora 30. All the packages had downloaded, all that was left was to let DNF reboot the machine and install all the new packages. I started the process and meandered off to find a cup of coffee: black, and darker than the stain this line of work leaves on the soul. After enough time had elapsed, I returned, expecting the warming light of a newly upgraded desktop. Instead, all that greeted me was the harsh darkness of a grub command line. Something was amiss, and it was bad.

(An aside to the reader, I had this experience on two different machines, stemming from two different root problems. One was a wayward setting, and the other an unusual permissions problem.)

How does the fledgling Linux sysadmin recover from such a problem? The grub command line is an inscrutable mystery to the uninitiated, but once you understand the basics, it’s not terribly difficult to boot your system and try to restore the normal boot process. This depends on what has broken, of course. If the disk containing your root partition has crashed, then sorry, this article won’t help.

In order to get a system booting, what exactly needs to happen? How does booting Linux work, even? Two components need to be loaded into memory: the kernel, and the initramfs. Once these two elements are loaded into memory, grub performs a jump into the kernel code, which takes over and finishes the machine’s boot. There is one more important detail that we care about — the kernel needs to know where to find the root partition. This is typically part of the kernel parameters, specified on the kernel boot line.

When working with an unfamiliar shell, the help command is a good starting point. grub runs in a very limited environment, and running the help command scrolls most of the text off the screen. There is an environment variable that helps out here, enabling output paging:set pager=1.
Continue reading “Tales From The Sysadmin: Dumped Into The Grub Command Line” →