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All details on this page supplied by:-

https://majek.sh/en/initrd-in-slackware/

Install everything, setup lilo, timezones etc as usual. At the end DON’T reboot at the end of setup – system isn’t finished yet!

Now, it’s time to prepare new initrd.

Chroot to /mnt (where new system should be already mounted)
Make copy of default mkinitrd config:


cp /etc/mkinitrd.conf.sample /etc/mkinitrd.conf


Edit new /etc/mkinitrd.conf with your favourite editor and set few options:

uncomment and set MODULE_LIST and ROOTFS to type of your root filesystem, for example


ROOTFS="ext3"


MODULE_LIST="ext3"


You don’t need to worry about all related modules, they will be added automatically.

if you use software raid, uncomment and set


RAID="1"
if you use lvm or encryption, uncomment and set


LVM="1"

I strongly recommend to set SOURCE_TREE and OUTPUT_IMAGE to some more unique names, for example


SOURCE_TREE="/boot/initrd-tree-3.10.12"


OUTPUT_IMAGE="/boot/initrd-3.10.12.gz"


You don’t have to do this if you don’t want to play with custom kernels etc.

make new initrd with mkinitrd -F


add initrd image to lilo.conf adding it just after ‘image’ line, so it will look like this:

<file init.img>
image = /boot/vmlinuz-generic-3.10.12
 initrd = /boot/initrd-3.10.12.gz
get out of chroot and rebuild lilo with:
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
lilo -r /mnt
</file>

Right now you could reboot system and enjoy new Slackware with initrd:-)

What’s an advantage of this way instead of running mkinitrd with many bizarre options? See next part.

Normal usage
Sometimes you need to change kernel, upgrade or something like that.

There are 2 ways of maintaining Slackware with initrd:

Use one initrd for all kernels
Use separate initrd for every kernel or even every entry in lilo
One initrd for all
At start, make sure that you have commented out CLEAR_TREE or set it to 0 in mkinitrd.conf!

After installation of new kernel and running still from old one, you need to to set KERNEL_VERSION to version of your new kernel, for example

KERNEL_VERSION="3.17.4"
Then just run mkinitrd -F
That’s all about initrd – now image has required modules for both/all your kernels.
Of course you need new entry in lilo.conf for new kernel with exactly the same initrd as old one.
If you are making kernel upgrade (replace old kernel package) you don’t even need to touch lilo.conf. But in both cases, you must run lilo at the end.

From time to time, you could clean initrd tree from old modules from kernel you don’t use anymore. In this case just remove all directory with that modules from /boot/initrd-tree/lib/modules/old-kernel-version and regenerate initrd using as usual mkinitrd -F. And rerun lilo of course 🙂

Now, you probably see advantage of using mkinitrd.conf instead of remembering all those weird switches you used last time to generate this image.

Separate initrd for every kernel
This way have a little sense if you only use one root filesystem and only stock kernel which you sometimes only upgrade.

Separate initrd is even easier than ‘one for all’ attitude.
One drawback is that mkinitrd with -F flag only reads one default /etc/mkinitrd.conf file, so each time you have to copy saved configuration back to this file.
So, for first kernel you should customize at least SOURCE_TREE, OUTPUT_IMAGE and KERNEL_VERSION. Generate new initrd with mkinitrd -F, then make backup of mkinitrd.conf to for example mkinitrd.conf.3.10.17.
For next kernel with different options customize mkinitrd.conf again, create new initrd, make backup and so on.
That way you could have different initrds and saved all options to regenerate each of them. It’s safe attitude as playing with new kernel and initrd configuration you always have working old one.

all content below here from:-

https://www.thegeekstuff.com/2009/07/how-to-view-modify-and-recreate-initrd-img/


How to View, Modify and Recreate initrd.img
by SASIKALA on JULY 10, 2009
Question: How do I view, modify and recreate the new initrd.img on Ubuntu, Debian, CentOS, Fedora, Red-Hat, Arch Linux, or SUSE distributions?


1. How To View Content Of initrd.img file?
initrd.img is in gzip format.  So move initrd.img to initrd.gz as shown below.

# cp /tftpboot/el5/initrd.img  .

# ls
cdrom   initrd.img

# mv initrd.img initrd.gz
Unzip the initrd.gz file as shown below.

# gunzip initrd.gz

# ls
cdrom  initrd
After unziping the initrd.gz file, the initrd is further in cpio ‘newc’ format. So extract the files from initrd using cpio ‘newc’ format as shown below.
Note: info cpio will give more information about ‘newc’ format.

# mkdir tmp2

# cd tmp2/

# cpio -id < ../initrd
16524 blocks
Now you can view the content of initrd.img file

# ls
bin  dev  etc  init  modules proc  sbin  selinux  sys  tmp  var
2. How To Modify Content of Image and Recreate New Image?
After extracting the file as shown below, make appropriate modification to any of those files. Then pack the files back into the archive using the following commands. Pack the modified files back to cpio ‘newc’ format.

# find . | cpio --create --format='newc' > /tmp/newinitrd
16524 blocks

# ls /tmp/
cdrom  initrd  newinitrd  tmp2

# ls -l /tmp/newinitrd
-rw-r--r-- 1 root root 8460288 Jul  2 14:50 /tmp/newinitrd
Gzip the archive file.

# gzip newinitrd

# ls
cdrom  initrd  newinitrd.gz  tmp2

# ls -l newinitrd.gz
-rw-r--r--  1 root root 6649867 Jul  2 14:50 newinitrd.gz
Move file as an image file. You can use the newinitrd.img as your new boot image.

# mv newinitrd.gz newinitrd.img

# ls -l newinitrd.img
-rw-r--r-- 1 root root 6649867 Jul  2 14:50 newinitrd.img

all content below here from:-

https://access.redhat.com/solutions/24029

How to unpack/uncompress and repack/re-compress an initial ramdisk (initrd/initramfs) boot image file on RHEL 5,6 ?
 SOLUTION VERIFIED - Updated August 7 2024 at 7:03 AM - English 
Environment
Red Hat Enterprise Linux 6
Red Hat Enterprise Linux 5
Note: For RHEL7 and RHEL8, refer to How to extract the contents of initramfs image on RHEL7?

Issue
How do I unpack or uncompress, and then repack or re-compress, an initrd or initramfs boot image file?
How do I modify the contents of an initrd or initramfs?
How do I view an initrd or initramfs?
Resolution
First, create a temporary work directory and switch into it. This will be the location where the initramfs/initrd contents will be viewed, edited, and re-compressed if required:

Raw
mkdir /tmp/initrd
cd /tmp/initrd
Identify compression format of the image
Use the file command on the initramfs/initrd to identify the compression format:

Raw
file /boot/initramfs-$(uname -r).img
The $(uname -r) will use the file for the current kernel version. You may also specify a specific file, such as:

Raw
file /boot/initramfs-2.6.32-754.el6.x86_64.img
The most common is a gzip-format image which displays as:

Raw
# file /boot/initramfs-$(uname -r).img
/boot/initramfs-2.6.32-754.el6.x86_64.img: gzip compressed data
However, there may also be an XZ/LZMA-format image which displays as:

Raw
# file /boot/initramfs-$(uname -r).img
/boot/initramfs-2.6.32-754.el6.x86_64.img: LZMA compressed data
Select the appropriate instructions below to extract or repack the correct image type for your system.

gzip format - Extract / Uncompress
Uncompress and extract the contents of the image in the /boot/ directory:

Raw
zcat /boot/initrd-$(uname -r).img | cpio -idmv
gzip format - Repack / Recompress
Still in the working directory, find all files and add them to a new boot image file:

Raw
find . | cpio -o -c -R root:root | gzip -9 > /boot/new.img
xz/LZMA format - Extract / Uncompress
Uncompress and extract the contents of the image in the /boot/ directory:

Raw
xz -dc < /boot/initrd-$(uname -r).img | cpio -idmv
xz/LZMA format - Repack / Recompress
Still in the working directory, find all files and add them to a new boot image file:

Raw
find . 2>/dev/null | cpio -o -c -R root:root | xz -9 --format=lzma > /boot/new.img
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