Use Generic Kernel with an Initrd

An initrd allows to use the smaller generic kernel instead of the huge kernel

This page is about initrd with the lilo boot loader. For EFI systems refer to Install Initrd on an UEFI boot system

Doc source: slackware/README.initrd

It seems better to generally use mkinitrd_command_generator.sh to create an initrd. See below at KVM. The rest of this section is obsolete.

On a locally available (with phsical access to keyboard and display) machine with ext4 on / the following should suffice:

cp -a /boot /boot.bak
cd /boot
mkinitrd -c -k 3.14.18-smp -m ext4 # use your kernel version here!

Now Edit lilo.conf :

image = /boot/vmlinuz -> image = /boot/vmlinuz-generic-smp
add initrd = /boot/initrd.gz

There is no need to update symlinks in /boot if you made sure, your lilo.conf point to the right generic kernel verion

An finally run lilo

According to linuxquestions the virtio kernel modules are necessary for KVM in the initrd.gz. A simple call like described in README.initrd, eg mkinitrd -c -k 3.10.17 -m ext4 will not include the virtio modules (tested) ⇒ Use /usr/share/mkinitrd/mkinitrd_command_generator.sh. In http://docs.slackware.com/howtos:slackware_admin:systemupgrade mkinitrd_command_generator.sh is mentioned as well

Check if you made a copy of /boot and generate the command which generates an initrd:

cd /boot # just to have everything togehter in /boot
/usr/share/mkinitrd/mkinitrd_command_generator.sh -k 4.4.14 > generated_mkinitrd_command-4.4.14

Important: Append the kernel version number to the name of the initrd output file in generated_mkinitrd_command-4.4.14 in order to not overwrite the existing initrd for the old proved kernel!

Now generate the initrd:

chmod +x generated_mkinitrd_command-4.4.14
./generated_mkinitrd_command-4.4.14

Fix lilo.conf and reinstall lilo:

cd /etc
cp lilo.conf lilo.conf.bak

The output of

/usr/share/mkinitrd/mkinitrd_command_generator.sh -l /boot/vmlinuz-generic-4.4.14

may be included in lilo.conf, to create a section for the new kernel (before the old kernel)

There is no need to update symlinks in /boot if you made sure, your lilo.conf point to the right kernel version. Finally run lilo:

lilo

To use the recommended generic instead of the huge kernel you have to build an initrd. This section is based on slackware-13.1/README.initrd

Make a copy of /boot dir to be on the save side: cp -a /boot /boot.org

Create the initial ramdisk filesystem /boot/initrd.gz with

mkinitrd -c -k 2.6.33.4-smp -m ext3 -f ext3 -r /dev/sda2

In this example we have an ext3 root „/“ partition on /dev/sda2 (see ls -al /dev/root) for a kernel of version 2.6.33.4-smp (See uname -r).
Or

mkinitrd -c -k 2.6.33.4-smp -m reiserfs

for Reiserfs, or

mkinitrd -c -k 2.6.33.4-smp -m ext4 -f ext4 -r /dev/sda2

for ext4 on /dev/sda2

It is not necessary to change the symlinks in /boot

Add a new image-section at the beginning of the image sections to /etc/lilo.config:

image = /boot/vmlinuz-generic-smp-2.6.33.4-smp
  initrd  = /boot/initrd.gz
  root= /dev/sda2
  label = LinuxGeneric
  read-only

Run lilo and restart.