Booting Linux from Flash
I like my computers to be as quiet as possible: if a computer is emitting very little sound, that makes it easier to live with. The noise a computer makes is especially important when it's in a home theatre situation, or acting as a media server; if a HTPC is itself throwing out lots of noise, that detracts from the sound of the movie being played.
The ideal case, of course, is for there to be no moving parts: things that move or spin inevitably have friction, and that causes noise. I've tried to eliminate everything that spins from my setup: I have a CPU that doesn't need a fan on the heatsink, and a fanless power supply. However, there's one thing left that is spinning, and that's the hard disk which hosts the Linux installation. Dropping that would make my system truly silent, so I started looking into how that could be done.
The only viable choice for a non-spinning medium to host the operating system is a USB Flash drive: most motherboard BIOSes have the ability to boot from a Flash device, and there's no other medium which is easily available in the sizes required. So the choice was obvious: copy the operating system from hard disk to Flash, and boot it from there.
Unfortunately, it's not quite that easy. In order for the BIOS to understand the Flash disk and boot from it, the disk must be formatted in a very simple format: specifically, good old FAT32. It's quite unacceptable for a Linux root filesystem to be based on FAT32, so a certain process has to be run through:
* Compress the root filesystem down into a disk image
* Boot the Linux kernel from a FAT-formatted Flash disk
* Get the kernel to mount the compressed image
* Continue booting from that image
What you'll need
Each step will require its own tools to get the job done, and I'll be covering the details behind each of these tools when they're used. In the meantime, here's a short list of everything that will be employed:
SquashFS tools:
We'll be using SquashFS to compress the root filesystem into an image, and the SquashFS make-filesystem tool will be needed for that.
SysLinux:
Getting Linux to boot from a FAT-formatted disk is no mean feat, unless you use SysLinux; it makes everything so much easier.
BusyBox:
In order for Linux to boot the filesystem image, it'll need to mount, cd and pivot_root, among other things. BusyBox provides all these tools in one go, as I'll explain in more detail later.
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I like my computers to be as quiet as possible: if a computer is emitting very little sound, that makes it easier to live with. The noise a computer makes is especially important when it's in a home theatre situation, or acting as a media server; if a HTPC is itself throwing out lots of noise, that detracts from the sound of the movie being played.
The ideal case, of course, is for there to be no moving parts: things that move or spin inevitably have friction, and that causes noise. I've tried to eliminate everything that spins from my setup: I have a CPU that doesn't need a fan on the heatsink, and a fanless power supply. However, there's one thing left that is spinning, and that's the hard disk which hosts the Linux installation. Dropping that would make my system truly silent, so I started looking into how that could be done.
The only viable choice for a non-spinning medium to host the operating system is a USB Flash drive: most motherboard BIOSes have the ability to boot from a Flash device, and there's no other medium which is easily available in the sizes required. So the choice was obvious: copy the operating system from hard disk to Flash, and boot it from there.
Unfortunately, it's not quite that easy. In order for the BIOS to understand the Flash disk and boot from it, the disk must be formatted in a very simple format: specifically, good old FAT32. It's quite unacceptable for a Linux root filesystem to be based on FAT32, so a certain process has to be run through:
* Compress the root filesystem down into a disk image
* Boot the Linux kernel from a FAT-formatted Flash disk
* Get the kernel to mount the compressed image
* Continue booting from that image
What you'll need
Each step will require its own tools to get the job done, and I'll be covering the details behind each of these tools when they're used. In the meantime, here's a short list of everything that will be employed:
SquashFS tools:
We'll be using SquashFS to compress the root filesystem into an image, and the SquashFS make-filesystem tool will be needed for that.
SysLinux:
Getting Linux to boot from a FAT-formatted disk is no mean feat, unless you use SysLinux; it makes everything so much easier.
BusyBox:
In order for Linux to boot the filesystem image, it'll need to mount, cd and pivot_root, among other things. BusyBox provides all these tools in one go, as I'll explain in more detail later.
Discuss Add this link to... Bury
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