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# dracut

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Related articles

- booster
- mkinitcpio
- Unified kernel image

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 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.

## Usage

`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.

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

### 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).

## Advanced configuration

It is important to note that there are two distinct approaches how the various tasks during initial ramdisk phase are performed:

Shell (bash/busybox/dash/ksh) based initial ramdisk
  An init script is started that in turn scans the filesystem of the initial ramdisk for dracut scripts to be executed.

Systemd based (default) initial ramdisk
  Systemd is already started at the beginning of the initial ramdisk phase. The tasks to be executed are detemined by regular systemd unit files. See systemd bootup process.

The concrete variant is determined by the absence or presence of the systemd dracut module. See #dracut modules for more details.

`dracut` can be configured by directly passing arguments on the command line (see dracut(8) § OPTIONS). 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+=" systemd "

You can see more configuration options with dracut.conf(5). Fuller descriptions of each option can be found with dracut(8). We will describe a few common options in what follows.

### dracut modules

dracut uses a modular approach to build the initramfs (see dracut.modules(7)). All of dracut 's builtin modules are located in `/lib/dracut/modules.d` and can be listed with `dracut --list-modules`. Extra modules can be provided by external packages e.g. dracut-sshd-gitAUR. dracut 's built-in modules unfortunately lack documentation, although their names can be self-explanatory.

Some of the modules are active/inactive by default, and can be activated/deactivated with `--add`/`--omit` command line argument or with the `add_dracutmodules+=""`/`omit_dracutmodules+=""` persistent config entry lines.

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

    # ...
    add_dracutmodules+=" dracut modules to activate "
    omit_dracutmodules+=" dracut modules to deactivate "
    # ...

The following table lists dracut modules, required packages (dracut 's optional dependencies) and module descriptions.

Most dracut modules are dependent on other dracut modules. As an example the bluetooth dracut module depends on the dbus dracut module. The table below only lists direct dracut module dependencies, i.e. the required packages for a given module listed in the `module-setup.sh` for the given dracut module.

Dracut modules not meant to be used on Arch Linux (e.g. ifcfg) are intentionally omitted in the table below.

For additional dracut module documentation, see the upstream dracut wiki.

dracut module | Required packages | Description
--- | --- | ---
bluetooth | bluez | Bluetooth (keyboard)
btrfs | btrfs-progs | Scans for Btrfs on block devices
busybox | busybox | Allows use of BusyBox (on your own risk)
crypt | cryptsetup | Support for encrypted Dm-crypt file systems
dash | dash | Allows use of Dash (on your own risk)
dmraid | dmraid, multipath-tools | dmraid dracut module support
mksh | mkshAUR | mksh dracut module support (on your own risk)
multipath | multipath-tools | Multipath dracut module support
dmsquash-live-ntfs | fuse3, ntfs-3g | Live on NTFS
lvm | lvm2 | Support for LVM
mdraid | mdadm | Support MD devices, also known as software RAID devices
memstrack | memstrackAUR | Support memstrack
nvdimm | ndctl | NVDIMM support
plymouth | plymouth | Plymouth boot splash
rescue |  | Includes various utilities for rescue mode (such as ping, ssh, vi, fsck.*)
resume |  | Allows initramfs to resume from low-power state
rngd |  | Starts random generator service on early boot
syslog | rsyslogAUR | Enable logging with Rsyslog
squash | squashfs-tools | Support for building a squashed initramfs
tpm2-tss | tpm2-tools | Trusted Platform Module
base |  | Base module with required utilities
bash | bash | Bash is the preferred interpreter, if there are more available
biosdevname | biosdevnameAUR | Enables BIOS network device renaming
caps |  | Supports dropping capabilities before init
convertfs |  | Merges / into /usr on next boot
crypt-gpg | gnupg | Adds support GPG for crypto operations and SmartCards (may requires GPG keys)
crypt-loop |  | Adds support for encrypted loopback devices (symmetric key)
dbus |  | Virtual package for dbus-broker or dbus-daemon
dbus-broker | dbus-broker | Use dbus-broker as dbus service provider
dbus-daemon | dbus | Use dbus as dbus service provider
debug |  | Enable debug features
dm |  | Adds support of device-mapper
dmsquash-live-autooverlay |  | Creates a partition for overlayfs usage in the free space on the root filesystem's parent block device
dracut-systemd |  | Base systemd dracut module
drm |  | Includes kernel modules that provides DRM support
ecryptfs |  | Adds ecryptfs filesystems support
fido2 |  | Allows to unlock an encrypted filesystem using a FIDO2 security token
fips |  | Enforces FIPS security standard regulations
fs-lib |  | Library for filesystem tools (including fsck.* and mount)
fstab-sys |  | Arranges for arbitrary partitions to be mounted before rootfs
i18n |  | Includes keymaps, console fonts, etc.
img-lib |  | Library to includes various tools for decompressing images
integrity |  | Adds support for Extended Verification Module
kernel-modules |  | Kernel modules for root filesystems and other boot-time devices
kernel-modules-extra |  | Extra out-of-tree kernel modules
lunmask |  | Masks LUN devices to select only ones which required to boot
lvmmerge |  | Merges lvm snapshots
lvmthinpool-monitor |  | Monitor LVM thinpool service
masterkey |  | Masterkey that can be used to decrypt other keys and keyutils
modsign |  | Adds signing kernel modules support
overlayfs |  | Kernel module for overlayfs
pcsc |  | Adds support for PCSC Smart cards
pkcs11 |  | Includes PKCS#11 libraries
pollcdrom |  | Enables CD-ROM polling
qemu |  | Includes kernel modules for QEMU environment
rescue |  | utilities for rescue mode (such as ping, ssh, vi, fsck.*)
rootfs-block |  | Arranges for the block device containing the rootfs to be mounted
securityfs |  | Arranges for the securityfs to be mounted early
selinux |  | Arranges for the selinux policy to be loaded
shutdown |  | Sets up hooks to run on shutdown
systemd |  | Adds systemd as early init initialization system
terminfo |  | Includes a terminfo file
udev-rules |  | Includes udev and some basic rules
uefi-lib |  | Library to include UEFI tools
usrmount |  | Mounts /usr
virtfs |  | Adds virtual filesystems (9p) support
virtiofs |  | Adds virtiofs filesystems support
warpclock |  | Sets kernel's timezone and reset the system time if adjtime is set to LOCAL
watchdog |  | Includes watchdog devices management; works only if systemd not in use
watchdog-modules |  | Includes watchdog kernel modules to be loaded early in booting

Dracut modules that are meant to be used when IP address is expected to be available during early boot.

networking dracut module | Required packages | Description
--- | --- | ---
cifs | cifs-utils | Support for Samba
nbd | nbd | Support network block devices
network-manager | networkmanager | NetworkManager support
nfs | nfs-utils | NFS support - NFSv3 and NFSv4
nvmf | nvme-cli, jq | NVMe over Fibre Channel and NVMe-over Fabrics support (NVMeoF only with dracut-gitAUR)
iscsi | open-iscsi | ISCSI support
ssh-client | openssh | Installs ssh and scp along with config files and specified keys
network-legacy | dhclient, iproute2, iputils | Legacy network support
connman | connman | Support for ConnMan networking
kernel-network-modules |  | Includes and loads kernel modules for network devices
livenet |  | Fetch live updates for SquashFS images
network |  | Virtual module for network service providers
url-lib |  | Library to includes curl and SSL certs
qemu-net |  | Includes network kernel modules for QEMU environment
systemd-network-management |  | Adds network management for systemd. Includes systemd-networkd, systemd-resolved and some othr networking related dracut modules
systemd-networkd |  | Systemd-networkd
net-lib |  | Networking library with ip (only with dracut-gitAUR)

#### TPM2

To make use of systemd 's unlocking of luks2 encrypted volumes using TPM2 through systemd-cryptenroll, install tpm2-tools package and enable the `tpm2-tss` dracut module.

### Early kernel module loading

Dracut enables early loading (at the initramfs stage, via `modprobe`) through its `--force_drivers` command or `force_drivers+=""` config entry line. For example:

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

    # ...
    force_drivers+=" nvidia nvidia_modeset nvidia_uvm nvidia_drm "
    # ...

### Kernel command line options

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/arch/root rootfstype=ext4 rootflags=rw,relatime"

#### Miscellaneous notes

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`
  Warning: `rd.cmdline=ask` may cause an issue where the keyboard is not yet initialized prior to its prompt forcing a hard reset. See dracut-ng issue 164. Fixed in dracut-gitAUR .
- Print informational output even if `quiet` is set: `rd.info`

### Unified kernel image

dracut can produce unified kernel images with the `--uefi` command line option or with the `uefi="yes"` configuration option.

## Tips and tricks

### 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_or_uefi_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.

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"

### Performance considerations

Some considerations to optimize the boot and initramfs creation performance are:

- Understand and configure the fastest compression. If the kernel modules are already compressed, perhaps there is no need to re-compress the initramfs on creation.

- Understand the impact if including systemd into your initramfs. If it slows things down, omit it. If it makes things faster, include it.

- Consider using dracut-cpio (available in dracut-gitAUR ). See the `--enhanced-cpio` option for applicability.

- Minimize the number of kernel modules and dracut modules included in initramfs. As an example: If nfs-utils is installed (but not required to boot), then you need to explicitly omit the nfs dracut module, otherwise network boot will be enabled in the generated initramfs in default configuration - see https://github.com/dracut-ng/dracut-ng/pull/297.

- Consider using busybox instead of bash.

- Consider hostonly.

### 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-ukifyAUR package is the modern way to generate a unified kernel image using systemd-ukify. Unlike the methods below, you can sign your whole kernel image including the initramfs. Using the `uefi_secureboot_cert` and `uefi_secureboot_key` options in your dracut config (dracut.conf(5)).
- The dracut-hookAUR package includes hooks and scripts similar to the below. Alternatively, you may want dracut-uefi-hookAUR or 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

### Bluetooth keyboard support

Dracut will enable the bluetooth module automatically when a bluetooth keyboard is detected. However it is required that dracut is in hostonly mode for this. This seems to not be the default. To enable hostonly mode you can add the following to your dracut configuration:

    hostonly=yes

## Troubleshooting

### 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 "

If applicable to your system, you may also want to see instructions to resume from an encrypted swap partition including the dracut specific instructions.

### LVM / software RAID / LUKS

If the kernel has issues auto discovering and mounting LVM / software RAID / LUKS blocks. You can retry generating an initramfs with the following kernel command line options:

    rd.auto rd.lvm=1 rd.dm=1 rd.md=1 rd.luks=1

### A stop job is running for "brltty"

If you have issues booting or very long shutdown processes while the system waits for `brltty`, add the following to the dracut configuration line:

    omit_dracutmodules+=" brltty "

Alternatively, uninstall brltty if it is not needed.

### No usable keyslot is available

    Cannot use whirlpool hash for keyslot encryption.
    Keyslot open failed.
    No usable keyslot is available.

A failure to boot with a message similar to the above typically will only require the user to include the `crypt` module via `add_dracutmodules`. However, if you continue to get the message after adding it, you may need to adjust your configuration with the following.

    install_items+=" /usr/lib/ossl-modules/legacy.so "

This is because OpenSSL deprecated the whirlpool hash and moved it to that library. Dracut does not automatically gather it when using Arch.

## See also

- Wikipedia:dracut (software)
- Gentoo:Dracut

Category:

- Initramfs