Why initrd is required?

Asked by: Deonte Cartwright I
Score: 4.3/5 (62 votes)

initrd provides the capability to load a RAM disk by the boot loader. This RAM disk can then be mounted as the root file system and programs can be run from it. Afterwards, a new root file system can be mounted from a different device.

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Beside the above, What is the use of initramfs?

Detailed Description. 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.

Also question is, What is the difference between initrd and initramfs?. 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.

In respect to this, 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.

Do I need a initramfs?

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.

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How do I stop initramfs?

Better just use the files directly from disk or flash. If your buffer cache is big enough they will stay in the buffer cache after the initial load anyway (and if your buffer cache is small you probably cannot afford to use initramfs at all).

How do I get rid of initramfs error?

Fix Busybox Initramfs Error On Ubuntu Linux
  1. To solve initramfs error on Ubuntu Linux, you need to repair the filesystem in the corrupted partition using fsck command like below: (initramfs) fsck /dev/sda1 -y. ...
  2. Now the fsck command will start to fix all bad blocks automatically in the filesystem.

How do I create an Initrd image for a custom kernel?

Here is a summary of the steps:
  1. Copy the resulting compiled kernel into your /boot directory using the name that resulted from your earlier changes to the Makefile. Here is an example: ...
  2. Edit /etc/lilo. ...
  3. Make a new initial ramdisk, initrd image (see the section called Making an initrd image) if needed.
  4. Run /sbin/lilo.

Where is initramfs stored?

Initramfs stands for Initial Random-Access Memory File System. On modern Linux systems, it is typically stored in a file under the /boot directory. The kernel version for which it was built will be included in the file name. A new initramfs is generated every time a new kernel is installed.

What does dracut stand for?

dracut is an event driven initramfs infrastructure. dracut (the tool) is used to create an initramfs image by copying tools and files from an installed system and combining it with the dracut framework, usually found in /usr/lib/dracut/modules. d.

What type of file is the initrd image file?

In the case of desktop or server Linux systems, the initrd is a transient file system. Its lifetime is short, only serving as a bridge to the real root file system. In embedded systems with no mutable storage, the initrd is the permanent root file system.

Is initramfs part of kernel?

The Linux kernel mounts the contents of initramfs as the initial root filesystem, before the real root (e.g. on your hard drive) is mounted. This initial root contains files needed to mount the real root filesystem and initialize your system—the most important bits being kernel modules.

What does vmlinuz stand for?

vmlinuz: vmlinuz is the name of the Linux kernel executable. vmlinuz is a compressed Linux kernel, and it loads the OS into memory so that the server becomes usable. vmlinuz = Virtual Memory LINUx gZip = Compressed Bootable Linux kernel Executable.

What is Rootfs image?

A rootfs image is just a file system image, that hosts at least an init system. For instance, our getting started guide uses an EXT4 FS image with OpenRC as an init system. Note that, whichever file system you choose to use, support for it will have to be compiled into the kernel, so it can be mounted at boot time.

How do you resolve a dracut error?

To resolve this issue, one or both of the following may be required, followed by rebuilding the initial ramdisk:
  1. Repair the LVM filter in /etc/lvm/lvm. conf to ensure it accepts the device associated with the root filesystem.
  2. Ensure that the root VG and LV paths references in the GRUB configuration are correct.

How do you debug a dracut problem?

This can be obtained by running the command dmsetup ls --tree. A list of block device attributes including vol_id compatible mode. This can be obtained by running the commands blkid and blkid -o udev. Turn on dracut debugging (see the 'debugging dracut' section), and attach all relevant information from the boot log.

How do you inspect initramfs?

How to inspect initramfs
  1. extract the microcode by cd path/to/initrd/; cpio -i </initrd. img and read the STDERR display (in my case 48).
  2. extract the basic initrd by cd path/to/initrad/; dd if=/initrd. img of=initrd. img bs=512 skip=48; zcat initrd. img |cpio -i (adjust skip values matching the cpio STDERR output).

How do I create a ramdisk image?

Making a generic ram disk
  1. Make sure ram disk support is compiled in your kernel. ...
  2. Create a ramdisk device if one does not already exist in /dev: ...
  3. Zero out the space you need on the ramdisk device: ...
  4. Make a file system on the ram disk, specifying the size: ...
  5. Mount the ram disk as you would a regular device:

What is sbin init?

The /sbin/init program (also called init ) coordinates the rest of the boot process and configures the environment for the user. When the init command starts, it becomes the parent or grandparent of all of the processes that start up automatically on the system.

How is a kernel made?

The open-source NASM, or the Net-Wide Assembler, will assemble the assembly code into a file format called object code. The object file generated is an intermediate step to produce the executable binary or program. ... All object code (created from your ASM and C files) will form bits and pieces of your kernel.

What is Busybox used for?

Busybox allows you or programs to perform actions on your phone using Linux (copied from Unix) commands. Android is basically a specialized Linux OS with a Java compatible (Dalvik) machine for running programs.

How do I run fsck from Initramfs?

For 17.10 or older...
  1. boot to the GRUB menu.
  2. choose Advanced Options.
  3. choose Recovery mode.
  4. choose Root access.
  5. at the # prompt, type sudo fsck -f /
  6. repeat the fsck command if there were errors.
  7. type reboot.

How long does it take to run fsck?

I would expect 5 hours for the fsck to complete.

Why is Ubuntu booting to Initramfs?

The “initramfs” error can affright you, but luckily this error has a very easy and straightforward solution. This error occurs when your memory got corrupted, especially the drive containing the operating system, and does not let it boot. To fix it, simply use the “file system consistency check” or “fsck” utility.

What is Initramfs in Kali?

Initramfs is the initial tmpfs-based file system in the RAM that doesn't use a separate block device. Like the initrd, it contains tools and scripts to mount file systems prior to calling init located in the root file system.