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On Fri 19 August 2011 13:12:25 frares@×××××.com did opine thusly: |
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> I the case I don't need a initram, I guess that the grub line for |
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> parameter passing to the kernel would be empty. Am I wrong? |
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Yes. |
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Using or not using kernel parameters has nothing to do with whether |
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you use an initramfs or not. |
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It's the initrd line in grub you do not need. |
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> |
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> I was just looking on how to build my own initram. What is it |
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> supposed to do anyway? |
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First, it's initramfs (the previous incarnation was initrd). You |
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should use the correct name. |
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An initramfs is a filesystems image stored on disk in a place that |
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grub can find. It contains a kernel, essential drivers and other bits |
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and pieces. When booting, grub finds the image, bangs it into memory |
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and instructs the cpu to start executing at a known point. |
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Why is this useful? |
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For Gentoo it usually isn't (there are times when it is - see below). |
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Binary distros like Ubuntu and Fedora absolutely require this. These |
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distros do not know what hardware you have and what drivers you |
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require, so they supply drivers for everything. But Ubuntu cannot |
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possibly compile into the kernel every possible driver you might need |
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to boot as the list would be huge (every known floppy, CD, USB, every |
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known MFM, IDE, SATA, SCSI, netboot, Fibre and more driver for a |
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start), so what they do instead is probe the hardware at boot time, |
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find out what you have, and load the driver modules you DO need. |
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This is the problem. The kernel wants to load disk drivers so that it |
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can access the disk and continue booting. Where are the drivers? Well, |
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they are on the disk. Oops, circular problem. |
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The difficulty is not finding and loading drivers, it's how do you get |
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the disk driver off the disk before you have the disk driver in |
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memory? (think chicken and egg here). |
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|
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An initramfs solves this nicely. Grub shoved a disk image into memory |
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when it booted. The kernel knows how to access it's memory it doesn't |
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need a driver for that. And now the files containing the needed |
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drivers are on a virtual disk *in memory*. The kernel loads them, and |
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can now access the real physical disks. |
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Lots more complicated stuff then happens, like getting rid of the |
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virtual filesystem from the initramfs and mounting the real filesystem |
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from disk at /, but that's beyond the scope of this mail. |
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Gentoo mostly doesn't need any of this because you do know your |
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hardware and can just compile your disk drivers into the kernel - this |
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is the very thing that Ubuntu cannot do. |
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Some Gentoo users still need an initramfs, such as booting off drives |
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in a RAID configuration. They need the RAID drivers first to read the |
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disks so use an initramfs to fix this little problem exactly as Ubunut |
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fixes their problem. |
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Make sense? |
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-- |
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alan dot mckinnon at gmail dot com |
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