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+
+Slackware initrd mini HOWTO
+by Patrick Volkerding, volkerdi@slackware.com
+Sun Jul 12 23:23:24 CDT 2009
+
+This document describes how to create and install an initrd, which may be
+required to use the 2.6 kernel. Also see "man mkinitrd".
+
+1. What is an initrd?
+2. Why to I need an initrd?
+3. How do I build the initrd?
+4. Now that I've built an initrd, how do I use it?
+
+
+1. What is an initrd?
+
+Initrd stands for "initial ramdisk". An initial ramdisk is a very small
+Linux filesystem that is loaded into RAM and mounted as the kernel boots,
+and before the main root filesystem is mounted.
+
+2. Why do I need an initrd?
+
+The usual reason to use an initrd is because you need to load kernel
+modules before mounting the root partition. Usually these modules are
+required to support the filesystem used by the root partition (ext3,
+reiserfs, xfs), or perhaps the controller that the hard drive is attached
+to (SCSI, RAID, etc). Essentially, there are so many different options
+available in modern Linux kernels that it isn't practical to try to ship
+many different kernels to try to cover everyone's needs. It's a lot more
+flexible to ship a generic kernel and a set of kernel modules for it.
+
+3. How do I build the initrd?
+
+The easiest way to make the initrd is to use the mkinitrd script included
+in Slackware's mkinitrd package. We'll walk through the process of
+upgrading to the generic 2.6.29.6 Linux kernel using the packages
+found in Slackware's slackware/a/ directory.
+
+First, make sure the kernel, kernel modules, and mkinitrd package are
+installed (the current version numbers might be a little different, so
+this is just an example):
+
+ installpkg kernel-generic-2.6.29.6-i686-2.txz
+ installpkg kernel-modules-2.6.29.6-i686-2.txz
+ installpkg mkinitrd-1.3.4-i486-3.txz
+
+Change into the /boot directory:
+
+ cd /boot
+
+Now you'll want to run "mkinitrd". I'm using reiserfs for my root
+filesystem, and since it's an IDE system the reiserfs module will be
+the only one I need to load:
+
+ mkinitrd -c -k 2.6.29.6 -m reiserfs
+
+This should do two things. First, it will create a directory
+/boot/initrd-tree containing the initrd's filesystem. Then it will
+create an initrd (/boot/initrd.gz) from this tree. If you wanted to,
+you could make some additional changes in /boot/initrd-tree/ and
+then run mkinitrd again without options to rebuild the image. That's
+optional, though, and only advanced users will need to think about that.
+
+Here's another example: Build an initrd image using Linux 2.6.29.6
+kernel modules for a system with an ext3 root partition on /dev/hdb3.
+Note that you need the mbcache, jbd, and ext3 modules to use ext3:
+
+ mkinitrd -c -k 2.6.29.6 -m mbcache:jbd:ext3 -f ext3 -r /dev/hdb3
+
+
+4. Now that I've built an initrd, how do I use it?
+
+Now that you've got an initrd (/boot/initrd.gz), you'll want to load
+it along with the kernel at boot time. If you use LILO for your boot
+loader you'll need to edit /etc/lilo.conf and add a line to load the
+initrd. Here's an example section of lilo.conf showing how this is
+done:
+
+# Linux bootable partition config begins
+image = /boot/vmlinuz-generic-2.6.29.6
+ initrd = /boot/initrd.gz
+ root = /dev/hda6
+ label = Lnx26296
+ read-only
+# Linux bootable partition config ends
+
+The initrd is loaded by the "initrd = /boot/initrd.gz" line.
+Just add the line right below the line for the kernel image you use.
+Save the file, and then run LILO again ('lilo' at the command line).
+You'll need to run lilo every time you edit lilo.conf or rebuild the
+initrd.
+
+Other bootloaders such as syslinux also support the use of an initrd.
+See the documentation for those programs for details on using an
+initrd with them.
+
+
+---------
+
+Have fun!