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--- initramfs [2013/06/04 10:07] – paulsmith
+++ initramfs [2013/06/04 10:13] (current) – paulsmith
@@ Line 1: / Line 1: @@
+====== initramfs ======
+===== 1. Create structure =====
+<code>
+mkdir /usr/src/initramfs
+cd /usr/src/initramfs
+mkdir -p bin lib dev etc mnt/root proc root sbin sys
+</code>
+===== 2. Build busybox =====
+<code>
+USE="static" emerge --root=/usr/src/initramfs/ -v busybox
+</code>
+===== 3. Copy minimal device nodes =====
+<code>
+cp -a /dev/{null,console,tty,sd??} /usr/src/initramfs/dev/
+</code>
+===== 4. Create /usr/src/initramfs/init =====
+<code>
+#!/bin/busybox sh
+# Mount the /proc and /sys filesystems.
+mount -t proc none /proc
+mount -t sysfs none /sys
+#setup mdev
+echo /sbin/mdev > /proc/sys/kernel/hotplug
+/sbin/mdev -s
+# Do your stuff here.
+echo "This script mounts rootfs and boots it up, nothing more!"
+rescue_shell() {
+    echo "Something went wrong. Dropping you to a shell."
+    busybox --install -s
+    exec /bin/sh
+}
+uuidlabel_root() {
+    for cmd in $(cat /proc/cmdline) ; do
+        case $cmd in
+        root=*)
+            dev=${cmd#root=}
+            type=${dev%%=*}
+            if [ $type = "LABEL" ] || [ $type = "UUID" ] ; then
+                mount -o ro $(findfs "$dev") /mnt/root
+            else
+                mount -o ro ${dev} /mnt/root
+            fi
+            ;;
+        esac
+    done
+}
+# Mount the root filesystem.
+uuidlabel_root || rescue_shell
+# Clean up.
+umount /proc
+umount /sys
+# Boot the real thing.
+exec switch_root /mnt/root /sbin/init
+</code>
+<code>
+chmod +x /usr/src/initramfs/init
+</code>
+===== 5. Installing options =====
+====== 5.1. Built into kernel (my prefered way) ======
+<code>
+cd /usr/src/linux
+make menuconfig
+General setup  --->
+  [*] Initial RAM filesystem and RAM disk (initramfs/initrd) support
+  (/usr/src/initramfs) Initramfs source file(s)
+make -j4 && make modules_install
+</code>
+====== 5.2. Build a initrd for grub ======
+cd /usr/src/initramfs/
+find . -print0 | cpio --null -ov --format=newc | gzip -9 > /boot/initramfs.cpio.gz
+edit grub < 1.0(add the initrd line):
+<code>
+  title Gentoo
+  root (hd0,0)
+  kernel /kernel64
+  initrd /initramfs.cpio.gz
+</code>
+edit grub > 2
+<code>
+menuentry 'Gentoo 64 Linux (UUID)' {
+        root=hd0,1
+        linux /boot/kernel64 root=UUID=d2e3c17f-75db-4c95-87ce-760c8e41e2ca
+        initrd  /boot/initramfs.cpio.gz
+}
+</code>