Problem extracting the "initrd" archive in kernel 5.4

Question

I can see my initrd is occupied almost 90 MB of disk but after extracting it via cpio , it contains only a 30 KB microcode :

$ cpio -it < initrd.img-5.4.0-18-generic 
.
kernel
kernel/x86
kernel/x86/microcode
kernel/x86/microcode/AuthenticAMD.bin
62 blocks

I know that there should be a lot of files and tools which are needed by the kernel in the first stage of booting , but I cannot find anything useful in it.

$ file initrd.img-5.4.0-18-generic 
initrd.img-5.4.0-18-generic: ASCII cpio archive (SVR4 with no CRC)

I took a look at here and here and this question but these are too old and don't work for me.My initrd.img is not a gzip archive .
How to extract that file properly?
I use kernel v.5.4.0

Thanks.

Answer 1

initramfs images contain multiple cpio archives; the name of your file suggests you’re using a Ubuntu derivative, so the simplest option for you to list the full contents is to use lsinitramfs:

lsinitramfs initrd.img-5.4.0-18-generic

To extract the contents, use unmkinitramfs:

unmkinitramfs initrd.img-5.4.0-18-generic initramfs

This will extract all the files to the initramfs directory.