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While installing a linux distro (say centos), the following messages appear on console: Loading vmlinuz.... Loading initrd.imag .......

These files (vmlinuz and initrd.imag) are located under isolinux/ directory inside the ISO. It is clear that "Loading initrd.img" is expanding the given file system with required (small-set of) drivers.

I would like to know what happens exactly (in theory and possibly pointer to what kernel code does it) when "loading vmlinuz" while installing ?

Is there any relation (at code level) when we see the message (Uncompressing kernel...) while booting up (as boot loader comes here after installation completed)?

Thank you.

Sri

kee
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  • I believe those loading messages are from the bootloader and not from the Linux kernel. Furthermore, the bootloader doesn't expand the initrd at all - it just passes a pointer to it to the kernel and the kernel handles the 'unpacking'. – tangrs Oct 01 '13 at 12:02
  • May be a basic question. During installation does the bootloader exists? I assume syslinux/isolinux does the loading. Correct me if wrong. – kee Oct 01 '13 at 13:51
  • No, once it transfers control to the kernel, the bootloader is irrelevant and the kernel usually just overwrites the memory originally used by the bootloader. The `Uncompressing kernel...` message most likely is coming from the kernel decompressor which is part of the kernel image. – tangrs Oct 01 '13 at 13:53
  • "The Uncompressing kernel... message most likely is coming from the kernel". I agree to this. Am also looking to understanding what is happening when installing freshly, where we see the message "Loading vmlinuz". Because nothing would be there at this point, what exactly the "loading vmlinz" does? – kee Oct 01 '13 at 14:16
  • The `Loading vmlinuz` message is probably output by the bootloader as it loads the kernel image from the disc into memory. – tangrs Oct 02 '13 at 01:20

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