On Fri, Jan 31, 2003 at 12:42:22PM -0800, nate wrote: > Matt Price said: > > hi there, > > > > can someone help me figure out what exactly initrd is, and why > > kernels use it? I have looked through the docs, and I understand that > > it's thefile used for an initial ramdisk in some cases, but I don't > > understand why it would be used in some cases and not in others. So for > > inst ance, the demudi kernel I just installed seems to demand the use of > > initrd, and I take it GRUB needs an anitrd argument to load the kernel. > > But why don't my own self-compiled kernels require an initrd argument at > > boot (nor have an initrd file anywhere in /boot, as far as I can tell)? > > the initrd image usually holds a small basic set of drivers used to > get the system to a basic working state(disk controllers, filesystem > drivers, perhaps raid or LVM as well), so it can mount the root filesystem > and access the 'rest' of the drivers. > > I haven't looked into it much but I think it's primarily used so that > you can still use modules in the kernel, having everything built into > the kernel doesn't always work(some drivers may conflict, or may require > certain options to be passed to them to work). If you build your own > kernel for your own hardware, which it seems that you do(I do too) you > probably don't need initrd(I don't use it myself), since you can just build > your drivers directly into the kernel.
Even then it may be needed. Let's pretend you want your root filesystem on an LVM partition which in turn rests on a software RAID device. 1) The kernel boots. 2) RAID is built in, so the md devices autostart. Cool. 3) You activate the LVM groups. Oh wait, you need to mount /proc first. Where are you going to mount it? Uh ... In this scenario you must have an initrd to provide a small root fs on a ramdisk. vgchange and vgscan (+ libraries) must be included. Now step three goes like this: 3) mount initrd, mount /proc 4) Run vgscan 5) run vgchange to activate volume groups. 6) mount root filesystem using pivot_root. 7) continue the boot process ... HTH, -- Nathan Norman - Incanus Networking mailto:[EMAIL PROTECTED] A good plan today is better than a perfect plan tomorrow. -- Gen. George S. Patton, Jr. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
