initrd in desktop

README.adoc

@@ -1526,12 +1526,26 @@ The main ingredients to get this working are:
 +
 It is also possible to compress that image with other options.
 * `qemu -initrd`: make QEMU put the image into memory and tell the kernel about it.
-* `CONFIG_BLK_DEV_INITRD=y`: Compile the kernel with initrd support
+* `CONFIG_BLK_DEV_INITRD=y`: Compile the kernel with initrd support, see also: https://unix.stackexchange.com/questions/67462/linux-kernel-is-not-finding-the-initrd-correctly/424496#424496
 +
 Buildroot forces that option when `BR2_TARGET_ROOTFS_CPIO=y` is given
 
 https://unix.stackexchange.com/questions/89923/how-does-linux-load-the-initrd-image asks how the mechanism works in more detail.
 
+==== initrd in desktop distros
+
+Most modern desktop distributions have an initrd in their root disk to do early setup.
+
+The rationale for this is described at: https://en.wikipedia.org/wiki/Initial_ramdisk
+
+One obvious use case is having an encrypted root filesystem: you keep the initrd in an unencrypted partition, and then setup decryption from there.
+
+I think GRUB then knows read common disk formats, and then loads that initrd to memory with a `/boot/grub/grub.cfg` directive of type:
+
+    initrd	/initrd.img-4.4.0-108-generic
+
+Related: https://stackoverflow.com/questions/6405083/initrd-and-booting-the-linux-kernel
+
 ==== initramfs
 
 initramfs is just like initrd, but you also glue the image directly to the kernel image itself.