# dracut

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Related articles

- booster
- mkinitcpio

dracut creates an initial image used by the kernel for preloading the block device modules (such as IDE, SCSI or RAID) which are needed to access the root filesystem. Upon installing linux, you can choose between mkinitcpio and dracut. dracut is used by Fedora, RHEL, Gentoo, and Debian, among others. Arch uses mkinitcpio by default.

You can read the full project documentation for dracut in the kernel documentation.

## Installation

Install the dracut package, or dracut-gitAUR for the latest development version.

Tip: If dracut works on your machine after you test it, you can uninstall mkinitcpio.

## Configuration

If you wish to always execute dracut with a certain set of flags, you can save a specified configuration in a `.conf` file in `/etc/dracut.conf.d/`. For example:

    /etc/dracut.conf.d/myflags.conf

    hostonly="yes"
    compress="lz4"
    add_drivers+=" i915 "
    omit_dracutmodules+=" network iscsi "

You can see more configuration options with dracut.conf(5). Fuller descriptions of each option can be found with dracut(8).

### Kernel command line options

Note: Man page documentation poorly explains injecting files, and reads as if `/etc/cmdline.d` could/should be on your system. It (`/etc/cmdline.d`) is part of the initramfs filesystem, and dracut does not recognize a created system `/etc/cmdline.d` - thus creating this directory is pointless.

You can force dracut to use kernel command line parameters in the initramfs environment. Be aware that you should use the UUID naming scheme for specifying block devices.

It is not necessary to specify the root block device for dracut. From dracut.cmdline(7):

  The root device used by the kernel is specified in the boot configuration file on the kernel command line, as always.

However, it may be useful to set some parameters early, and you can enable additional features like prompting for additional command line parameters. See dracut.cmdline(7) for all options. Here are some example configuration options:

- Resume from a swap partition: `resume=UUID=80895b78-7312-45bc-afe5-58eb4b579422`
- Prompt for additional kernel command line parameters: `rd.cmdline=ask`
- Print informational output even if "quiet" is set: `rd.info`

Kernel command line options can be placed in a `*.conf` file in `/etc/dracut.conf.d/`, and set via the `kernel_cmdline=` flag. Dracut will automatically source this file and create a `01-default.conf` file and place it inside the initramfs directory `/etc/cmdline.d/`. For example, your kernel command line options file could look like:

    /etc/dracut.conf.d/cmdline.conf

    kernel_cmdline="rd.luks.uuid=luks-f6c738f3-ee64-4633-b6b0-eceddb1bb010 rd.lvm.lv=arch/root  rd.lvm.lv=arch/swap  root=/dev/mapper/arch-root rootfstype=ext4 rootflags=rw,relatime"

This file is also sourced by Dracut for unified kernel images. The resulting file (both initramfs.img and uefi.efi files) can be viewed with `lsinitrd` utilizing the `--unpackearly` option, eg:

`lsinitrd --unpackearly /boot/EFI/Arch/Arch.efi /etc/cmdline.d/01-default.conf | less`

## Usage

Note: The files created through these commands embed any installed Microcode images.

dracut is easy to use and typically does not require user configuration, even when using non-standard setups, like LVM on LUKS.

To generate an initramfs for the running kernel:

    # dracut --hostonly --no-hostonly-cmdline /boot/initramfs-linux.img

To generate a fallback initramfs run:

    # dracut /boot/initramfs-linux-fallback.img

`/boot/initramfs-linux.img` refers to the output image file. If you are using the non-regular kernel, consider changing the file name. For example, for the linux-lts kernel, the output file should be named `/boot/initramfs-linux-lts.img`. However, you can name these files whatever you wish as long as your boot loader configuration uses the same file names.

### Additional options

The `--force` flag overwrites the image file if it is already present.

The `--kver` option specifies which kernel to use. The argument to this option must match the name of a directory present in `/usr/lib/modules`.

More flags can be found with dracut(8).

## Tips and tricks

This article or section needs expansion.

Reason: Add instructions for creating a unified kernel image using the `--uefi` option. (Discuss in Talk:Dracut#Unified kernel image)

### View information about generated image

You can view information about a generated initramfs image, which you may wish to view in a pager:

    # lsinitrd /path/to/initramfs_image | less

This command will list the arguments passed to dracut when the image was created, the list of included dracut modules, and the list of all included files.

### Change compression program

To reduce the amount of time spent compressing the final image, you may change the compression program used.

Warning:

- Make sure your kernel has your chosen decompression support compiled in, otherwise you will not be able to boot. You must also have the chosen compression program package installed.
- The upstream Linux kernel does not support zstd compressed initramfs before version 5.9. linux-zen supports it since version 5.8

Simply add any one of the following lines (not multiple) to your dracut configuration:

    compress="cat"
    compress="gzip"
    compress="bzip2"
    compress="lzma"
    compress="xz"
    compress="lzo"
    compress="lz4"
    compress="zstd"

gzip is the default compression program used. `compress="cat"` will make the initramfs with no compression.

You can also use a non-officially-supported compression program:

    compress="program"

### Generate a new initramfs on kernel upgrade

It is possible to automatically generate new initramfs images upon each kernel upgrade. The instructions here are for the default linux kernel, but it should be easy to add extra hooks for other kernels.

Tip: The dracut-hookAUR package includes hooks and scripts similar to the below. Alternatively, you may want dracut-hook-uefiAUR instead, if you want an initramfs image that is an EFI executable (i.e. `esp/EFI/Linux/linux-kernel-machine_id-build_id.efi`). EFI binaries in this directory are automatically detected by systemd-boot and therefore do not need an entry in `/boot/loader/loader.conf`.

As the command to figure out the kernel version is somewhat complex, it will not work by itself in a pacman hook. So create a script anywhere on your system. For this example it will be created in `/usr/local/bin/`.

The script will also copy the new `vmlinuz` kernel file to `/boot/`, since the kernel packages do not place files in `/boot/` anymore.[1]

    /usr/local/bin/dracut-install.sh

    #!/usr/bin/env bash

    args=('--force' '--no-hostonly-cmdline')

    while read -r line; do
    	if [[ "$line" == 'usr/lib/modules/'+([^/])'/pkgbase' ]]; then
    		read -r pkgbase < "/${line}"
    		kver="${line#'usr/lib/modules/'}"
    		kver="${kver%'/pkgbase'}"

    		install -Dm0644 "/${line%'/pkgbase'}/vmlinuz" "/boot/vmlinuz-${pkgbase}"
    		dracut "${args[@]}" --hostonly "/boot/initramfs-${pkgbase}.img" --kver "$kver"
    		dracut "${args[@]}" --no-hostonly "/boot/initramfs-${pkgbase}-fallback.img" --kver "$kver"
    	fi
    done

    /usr/local/bin/dracut-remove.sh

    #!/usr/bin/env bash

    while read -r line; do
    	if [[ "$line" == 'usr/lib/modules/'+([^/])'/pkgbase' ]]; then
    		read -r pkgbase < "/${line}"
    		rm -f "/boot/vmlinuz-${pkgbase}" "/boot/initramfs-${pkgbase}.img" "/boot/initramfs-${pkgbase}-fallback.img"
    	fi
    done

You need to make the scripts executable. If you wish to add or remove flags, you should add them to your dracut configuration.

The next step is creating pacman hooks:

    /etc/pacman.d/hooks/90-dracut-install.hook

    [Trigger]
    Type = Path
    Operation = Install
    Operation = Upgrade
    Target = usr/lib/modules/*/pkgbase

    [Action]
    Description = Updating linux initcpios (with dracut!)...
    When = PostTransaction
    Exec = /usr/local/bin/dracut-install.sh
    Depends = dracut
    NeedsTargets

    /etc/pacman.d/hooks/60-dracut-remove.hook

    [Trigger]
    Type = Path
    Operation = Remove
    Target = usr/lib/modules/*/pkgbase

    [Action]
    Description = Removing linux initcpios...
    When = PreTransaction
    Exec = /usr/local/bin/dracut-remove.sh
    NeedsTargets

You should stop mkinitcpio from creating and removing initramfs images as well, either by removing mkinitcpio or with the following commands:

    # ln -sf /dev/null /etc/pacman.d/hooks/90-mkinitcpio-install.hook
    # ln -sf /dev/null /etc/pacman.d/hooks/60-mkinitcpio-remove.hook

## Troubleshooting

### Spaces in kernel parameters

dracut does not support quoted values with spaces in the `root=` and `resume=` kernel parameters. For example `root="PARTLABEL=Arch Linux"`. See dracut issue 720.

You will need to specify the parameters using a different block device naming scheme like UUID.

### Hibernation

If resuming from hibernation does not work, you may need to configure dracut to include the `resume` module. You will need to add a configuration file:

    /etc/dracut.conf.d/resume-from-hibernate.conf

    add_dracutmodules+=" resume "

## See also

- Wikipedia:dracut (software)
- Gentoo:Dracut

Category:

- Initramfs

Hidden category:

- Pages or sections flagged with Template:Expansion