What is difference between initrd and initramfs?

In sum, ramfs is just file opened and loaded into memory, isn’t it? Both initrd and ramfs are zipped at compile time, but the difference is, initrd is a block device unpacked to be mounted by the kernel at booting, while ramfs is unpacked via cpio into memory.

Why is initrd needed?

The initrd contain the modules required to understand the root filesystem, and thus be able to access the normal store of kernel modules. If your kernel is compiled with all that code built-in, rather than as modules, then an initrd shouldn’t be required.

What is vmlinuz and initrd?

The vmlinuz and initrd files are in a /boot directory. This directory is special — it is reserved for boot files, and the bootloader knows to look for this directory. It is generally a separate partition of the primary disk where the operating system is installed.

What initrd means?

The initial RAM disk (initrd) is an initial root file system that is mounted prior to when the real root file system is available. The initrd is bound to the kernel and loaded as part of the kernel boot procedure.

What is initrd IMG?

LINUX supports what is known as an initrd image ( initial rAM disk image). This is a small, +1.5 megabyte file system that is loaded by LILO and mounted by the kernel instead of the real file system. The kernel mounts this file system as a RAM disk, executes the file /linuxrc, and then only mounts the real file system.

What is Cpio initramfs?

The basic initramfs is the root filesystem image used for booting the kernel provided as a compressed cpio archive. This basic initramfs image may be prepended with an uncompressed cpio archive holding the microcode data loaded very early in the boot process.

Is initramfs necessary?

For many users, an initramfs system is of no concern. Their system uses a simple partitioning schema with no exotic drivers or setups (like encrypted file systems), so the Linux kernel is entirely capable of handing over control to the init binary on their system. But for many systems, an initramfs is mandatory.

How do I boot without initrd?

Booting the Linux Kernel Without an initrd/initramfs

  1. Remove initrd/initramfs support from the linux kernel.
  2. Remove UUIDs from kernel command line parameters and /etc/fstab .
  3. Build all modules into the linux kernel.
  4. Tell the bootloader where root is located and what filesystem it’s using.

What is difference between Vmlinux and vmlinuz?

vmlinux: A non-compressed and non-bootable Linux kernel file format, just an intermediate step to producing vmlinuz . vmlinuz: A compressed and bootable Linux kernel file.

How is initrd loaded?

The loading of initrd is handled by the boot loader (GRUB, LILO, etc.). Boot loaders only need BIOS routines to load data from the boot medium. If the boot loader is able to load the kernel, it can also load the initial ramdisk. Special drivers are not required.

What is initramfs in Linux?

Initramfs is used as the first root filesystem that your machine has access to. It is used for mounting the real rootfs which has all your data. The initramfs carries the modules needed for mounting your rootfs. But you could always compile your kernel to have these modules.

What is inside initrd?

The initrd contains various executables and drivers that permit the real root file system to be mounted, after which the initrd RAM disk is unmounted and its memory freed. In many embedded Linux systems, the initrd is the final root file system.