dracut

Harald Hoyer

This work is licensed under the Creative Commons Attribution/Share-Alike License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

2010

Table of Contents

1. Introduction

Definition
Rationale
Implementation
Mount preparations

2. User Manual

Creating an initramfs Image

Inspecting the Contents
Adding dracut Modules
Omitting dracut Modules
Adding Kernel Modules

Boot parameters

Specifying the root Device
Keyboard Settings
Blacklisting Kernel Modules
Speeding up the Boot Process
Injecting custom Files

Network Boot

Reducing the Image Size
NFS Root Device
iSCSI Root Device
FCoE Root Device

Troubleshooting

Identifying your problem area
Information to include in your report
Debugging dracut

3. Developer Manual

dracut Components

Boot Process Stages

Basic Setup
Hook: cmdline
Hook: pre-udev
Start Udev
Hook: pre-trigger
Trigger Udev
Main Loop
Hook: pre-mount
Hook: mount
Hook: pre-pivot
Cleanup and switch_root

Network Infrastructure

Writing a Module

check()
depends()
install()
installkernel()
Creation Functions
Initramfs Functions
Network Modules

A. Man Pages

dracut

dracut — create initial ramdisk images for preloading modules

dracut.conf

dracut.conf — configuration file(s) for dracut

dracut.kernel

dracut.kernel — dracut kernel command line options

Chapter 1. Introduction

This section is a modified version of http://en.wikipedia.org/wiki/Initrd, which is licensed under the Creative Commons Attribution/Share-Alike License.

Table of Contents

Definition
Rationale
Implementation
Mount preparations

Definition

An initial ramdisk is a temporary file system used in the boot process of the Linux kernel. initrd and initramfs refer to slightly different schemes for loading this file system into memory. Both are commonly used to make preparations before the real root file system can be mounted.

Rationale

Many Linux distributions ship a single, generic kernel image that is intended to boot as wide a variety of hardware as possible. The device drivers for this generic kernel image are included as loadable modules, as it is not possible to statically compile them all into the one kernel without making it too large to boot from computers with limited memory or from lower-capacity media like floppy disks.

This then raises the problem of detecting and loading the modules necessary to mount the root file system at boot time (or, for that matter, deducing where or what the root file system is).

To further complicate matters, the root file system may be on a software RAID volume, LVM, NFS (on diskless workstations), or on an encrypted partition. All of these require special preparations to mount.

Another complication is kernel support for hibernation, which suspends the computer to disk by dumping an image of the entire system to a swap partition or a regular file, then powering off. On next boot, this image has to be made accessible before it can be loaded back into memory.

To avoid having to hardcode handling for so many special cases into the kernel, an initial boot stage with a temporary root file system—now dubbed early user space—is used. This root file system would contain user-space helpers that would do the hardware detection, module loading and device discovery necessary to get the real root file system mounted.

Implementation

An image of this initial root file system (along with the kernel image) must be stored somewhere accessible by the Linux bootloader or the boot firmware of the computer. This can be:

The root file system itself
A boot image on an optical disc
A small ext2/ext3 or FAT-formatted partition on a local disk (a boot partition)
A TFTP server (on systems that can boot from Ethernet)

The bootloader will load the kernel and initial root file system image into memory and then start the kernel, passing in the memory address of the image.

Depending on which algorithms were compiled statically into it, the kernel can currently unpack initrd/initramfs images compressed with gzip, bzip2 and LZMA.

Mount preparations

dracut can generate a customized initrams image which contains only whatever is necessary to boot some particular computer, such as ATA, SCSI and filesystem kernel modules (host-only mode).

dracut can also generate a more generic initramfs image (default mode).

dracut's initramfs starts only with the device name of the root file system (or its UUID) and must discover everything else at boot time. A complex cascade of tasks must be performed to get the root file system mounted:

Any hardware drivers that the boot process depends on must be loaded. All kernel modules for common storage devices are packed onto the initramfs and then udev pulls in modules matching the computer's detected hardware.
On systems which display a boot rd.splash screen, the video hardware must be initialized and a user-space helper started to paint animations onto the display in lockstep with the boot process.
If the root file system is on NFS, dracut does then:
- Bring up the primary network interface.
- Invoke a DHCP client, with which it can obtain a DHCP lease.
- Extract the name of the NFS share and the address of the NFS server from the lease.
- Mount the NFS share.
If the root file system appears to be on a software RAID device, there is no way of knowing which devices the RAID volume spans; the standard MD utilities must be invoked to scan all available block devices with a raid signature and bring the required ones online.
If the root file system appears to be on a logical volume, the LVM utilities must be invoked to scan for and activate the volume group containing it.
If the root file system is on an encrypted block device:
- Invoke a helper script to prompt the user to type in a passphrase and/or insert a hardware token (such as a smart card or a USB security dongle).
- Create a decryption target with the device mapper.

dracut uses udev, an event-driven hotplug agent, which invokes helper programs as hardware devices, disk partitions and storage volumes matching certain rules come online. This allows discovery to run in parallel, and to progressively cascade into arbitrary nestings of LVM, RAID or encryption to get at the root file system.

When the root file system finally becomes visible:

Any maintenance tasks which cannot run on a mounted root file system are done.
The root file system is mounted read-only.
Any processes which must continue running (such as the rd.splash screen helper and its command FIFO) are hoisted into the newly-mounted root file system.

The final root file system cannot simply be mounted over /, since that would make the scripts and tools on the initial root file system inaccessible for any final cleanup tasks. On an initramfs, the initial root file system cannot be rotated away. Instead, it is simply emptied and the final root file system mounted over the top.

Chapter 2. User Manual

Creating an initramfs Image

To create a initramfs image, the most simple command is:

# dracut

This will generate a general purpose initramfs image, with all possible functionality resulting of the combination of the installed dracut modules and system tools. The image is /boot/initramfs-<kernel version>.img and contains the kernel modules of the currently active kernel with version <kernel version>.

If the initramfs image already exists, dracut will display an error message, and to overwrite the existing image, you have to use the --force option.

# dracut --force

If you want to specify another filename for the resulting image you would issue a command like:

# dracut foobar.img

To generate an image for a specific kernel version, the command would be:

# dracut foobar.img 2.6.40-1.rc5.f20

A shortcut to generate the image at the default location for a specific kernel version is:

# dracut '' 2.6.40-1.rc5.f20

If you want to create lighter, smaller initramfs images, you may want to specify the --host-only or -H option. Using this option, the resulting image will contain only those dracut modules, kernel modules and filesystems, which are needed to boot this specific machine. This has the drawback, that you can't put the disk on another controller or machine, and that you can't switch to another root filesystem, without recreating the initramfs image. The usage of the --host-only option is only for experts and you will have to keep the broken pieces. At least keep a copy of a general purpose image (and corresponding kernel) as a fallback to rescue your system.

Inspecting the Contents

To see the contents of the image created by dracut, you can use the lsinitrd tool.

# lsinitrd /boot/initramfs-$(uname -r).img | less

To display the contents of a file in the initramfs also use the lsinitrd tool:

# lsinitrd /boot/initramfs-$(uname -r).img  /etc/ld.so.conf
include ld.so.conf.d/*.conf

Adding dracut Modules

Some dracut modules are turned off by default and have to be activated manually. You can do this by adding the dracut modules to the configuration file /etc/dracut.conf or /etc/dracut.conf.d/myconf.conf. See the man page dracut.conf(5). You can also add dracut modules on the command line by using the -a or --add option:

# dracut --add bootchart initramfs-bootchart.img

To see a list of available dracut modules, use the --list-modules option:

# dracut --list-modules

or, if you have a dracut version earlier than 008, issue the command:

# for mod in /usr/share/dracut/modules.d/*; do echo ${mod##*/??}; done

Omitting dracut Modules

Sometimes you don't want a dracut module to be included for reasons of speed, size or functionality. To do this, either specify the omit_dracutmodules variable in the dracut.conf or /etc/dracut.conf.d/myconf.conf configuration file (see man page dracut.conf(5)), or use the -o or --omit option on the command line:

# dracut -o "multipath lvm" no-multipath-lvm.img

Adding Kernel Modules

If you need a special kernel module in the initramfs, which is not automatically picked up by dracut, you have the use the --add-drivers option on the command line or the drivers vaiable in the /etc/dracut.conf or /etc/dracut.conf.d/myconf.conf configuration file (see man page dracut.conf(5)):

# dracut --add-drivers mymod initramfs-with-mymod.img

Boot parameters

The generated initramfs.img file normally does not contain any system configuration files (except for some special exceptions), so the configuration has to be done on the kernel command line. With this flexibility, you can easily boot from a changed root partition, without the need to recompile the initramfs image. So, you could completly change your root partition (move it inside a md raid with encryption and LVM on top), as long as you specify the correct filesystem LABEL or UUID on the kernel command line for your root device, dracut will find it and boot from it.

The kernel command line usually can be configured in /boot/grub/grub.conf, if grub is your bootloader and it also can be edited in the real boot process in the grub menu.

The kernel command line can also be provided by the dhcp server with the root-path option. See the section called “Network Boot”.

For a full reference of all kernel command line parameters, see the dracut.conf(5) or dracut(8) man page.

Specifying the root Device

This is the only option dracut really needs to boot from your root partition. Because your root partition can live in various environments, there are a lot of formats for the root= option. The most basic one is root=<path to device node>:

root=/dev/sda2

Because device node names can change, dependent on the drive ordering, you are encouraged to use the filesystem identifier (UUID) or filesystem label (LABEL) to specify your root partition:

root=UUID=19e9dda3-5a38-484d-a9b0-fa6b067d0331

root=LABEL=myrootpartitionlabel

To see all UUIDs or LABELs on your system, do:

# ls -l /dev/disk/by-uuid

# ls -l /dev/disk/by-label

If your root partition is on the network see the section called “Network Boot”.

Keyboard Settings

If you have to input passwords for encrypted disk volumes, you might want to set the keyboard layout and specify a display font.

A typical german kernel command would contain:

vconsole.font=latarcyrheb-sun16 vconsole.keymap=de-latin1-nodeadkeys locale.LANG=de_DE.UTF-8

Setting these options can override the setting stored on your system, if you use a modern init system, like systemd.

For dracut versions prior to version 008 the line would look like:

LANG=de_DE.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=de-latin1-nodeadkeys

Blacklisting Kernel Modules

Sometimes it is required to prevent the automatic kernel module loading of a specific kernel module. To do this, just add rd.blacklist=<kernel module name>, with <kernel module name> not containing the .ko suffix, to the kernel command line. For example:

rd.blacklist=mptsas rd.blacklist=nouveau

The option can be specified multiple times on the kernel command line.

Speeding up the Boot Process

If you want to speed up the boot process, you can specify as much information for dracut on the kernel command as possible. For example, you can tell dracut, that you root partition is not on a LVM volume or not on a raid partition, or that it lives inside a specific crypto LUKS encrypted volume. By default, dracut searches everywhere. A typical dracut kernel command line for a plain primary or logical partition would contain:

rd.luks=0 rd.lvm=0 rd.md=0 rd.dm=0

on systems with dracut version prior to 008 the line would look like:

rd_NO_LUKS rd_NO_LVM rd_NO_MD rd_NO_DM

This turns off every automatic assembly of LVM, MD raids, DM raids and crypto LUKS.

Of course, you could also omit the dracut modules in the initramfs creation process, but then you would lose the posibility to turn it on on demand.

Injecting custom Files

To add your own files to the initramfs image, you have several possibilities.

The --include option let you specify a source path and a target path. For example

# dracut --include cmdline-preset /etc/cmdline initramfs-cmdline-pre.img

will create an initramfs image, where the file cmdline-preset will be copied inside the initramfs to /etc/cmdline. --include can only be specified once.

# mkdir rd.live.overlay
# mkdir rd.live.overlay/etc
# mkdir rd.live.overlay/etc/conf.d
# echo "ip=auto" >> rd.live.overlay/etc/cmdline
# echo export TESTVAR=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
# echo export TESTVAR=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
# tree rd.live.overlay/
rd.live.overlay/
└── etc
    ├── cmdline
    └── conf.d
        └── testvar.conf
# dracut --include rd.live.overlay / initramfs-rd.live.overlay.img

This will put the contents of the rd.live.overlay directory into the root of the initramfs image.

The --install option let you specify several files, which will get installed in the initramfs image at the same location, as they are present on initramfs creation time.

# dracut --install 'strace fsck.ext3 ssh' initramfs-dbg.img

This will create an initramfs with the strace, fsck.ext3 and ssh executables, together with the libraries needed to start those. The --install option can be specified multiple times.

Network Boot

If your root partition is on a network drive, you have to have the network dracut modules installed to create a network aware initramfs image.

On a Red Hat Enterprise Linux or Fedora system, this means, you have to install the dracut-network rpm package:

# yum install dracut-network

The resulting initramfs image can be served by a boot manager residing on your local hard drive or it can be served by a PXE/TFTP server.

How to setup your PXE/TFTP server can be found in the Red Hat Enterprise Linux Storage Administration Guide.

If you specify rd.ip=auto on the kernel command line, then dracut asks a dhcp server about the ip adress for the machine. The dhcp server can also serve an additional root-path, which will set the root device for dracut. With this mechanism, you have static configuration on your client machine and a centralized boot configuration on your TFTP/DHCP server. If you can't pass a kernel command line, then you can inject /etc/cmdline, with a method described in the section called “Injecting custom Files”.

Reducing the Image Size

To reduce the size of the initramfs, you should create it with by ommitting all dracut modules, which you know, you don't need to boot the machine.

You can also specify the exact dracut and kernel modules to produce a very tiny initramfs image.

For example for a NFS image, you would do:

# dracut -m "nfs network  base" initramfs-nfs-only.img

Then you would boot from this image with your target machine and reduce the size once more by creating it on the target machine with the --host-only option:

# dracut -m "nfs network base" --host-only initramfs-nfs-host-only.img

This will reduce the size of the initramfs image significantly.

NFS Root Device

iSCSI Root Device

FCoE Root Device

Troubleshooting

If the boot process does not succeed, you have several options to debug the situation. Some of the basic operations are covered here. For more information you should also visit: http://fedoraproject.org/wiki/How_to_debug_Dracut_problems

Identifying your problem area

Remove ''rhgb'' and ''quiet'' from the kernel command line
Add ''rd.shell'' to the kernel command line. This will present a shell should dracut be unable to locate your root device
Add ''rd.shell rd.debug'' to the kernel command line so that dracut shell commands are printed as they are executed
With dracut >= 002-11, you can inspect the rd.debug output with:
```
# less /run/initramfs/init.log
# dmesg | less
```

Information to include in your report

All bug reports

In all cases, the following should be mentioned and attached to your bug report:

The exact kernel command-line used. Typically from the bootloader configuration file (e.g. /etc/grub.conf) or from /proc/cmdline.
A copy of your disk partition information from /etc/fstab, which might be obtained booting an old working initramfs or a rescue medium.
A device listing from device-mapper. 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 -p
# blkid -p -o udev
```
Turn on dracut debugging (see the 'debugging dracut' section), and attach all relevant information from the boot log. This can be obtained by running the command
```
# dmesg|grep dracut
```
If you use a dracut configuration file, please include /etc/dracut.conf and all files in /etc/dracut.conf.d/*.conf

Logical Volume Management related problems

As well as the information from the section called “All bug reports” include the following information:

Include physical volume information by running the command:
```
# lvm pvdisplay
```
Include volume group information by running the command:
```
# lvm vgdisplay
```
Include logical volume information by running the command:
```
# lvm lvdisplay
```

Software RAID related problems

As well as the information from the section called “All bug reports”, include the following information:

If using software RAID disk partitions, please include the output of
```
# cat /proc/mdstat
```

Network root device related problems

This section details information to include when experiencing problems on a system whose root device is located on a network attached volume (e.g. iSCSI, NFS or NBD). As well as the information from the section called “All bug reports”, include the following information:

Please include the output of

# /sbin/ifup <interfacename>
# ip addr show

Debugging dracut

Configure a serial console

Successfully debugging dracut will require some form of console logging during the system boot. This section documents configuring a serial console connection to record boot messages.

First, enable serial console output for both the kernel and the bootloader.
Open the file /etc/grub.conf for editing. Below the line ''timeout=5'', add the following:
```
serial --unit=0 --speed=9600
terminal --timeout=5 serial console
```
Also in /etc/grub.conf, add the following boot arguemnts to the ''kernel'' line:
```
console=tty0 console=ttyS0,9600
```

When finished, the /etc/grub.conf file should look similar to the example below.

default=0
timeout=5
serial --unit=0 --speed=9600
terminal --timeout=5 serial console
title Fedora (2.6.29.5-191.fc11.x86_64)
  root (hd0,0)
  kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 console=ttyS0,9600
  initrd /dracut-2.6.29.5-191.fc11.x86_64.img

More detailed information on how to configure the kernel for console output can be found at http://www.faqs.org/docs/Linux-HOWTO/Remote-Serial-Console-HOWTO.html#CONFIGURE-KERNEL.

Redirecting non-interactive output

You can redirect all non-interactive output to /dev/kmsg and the kernel will put it out on the console when it reaches the kernel buffer by doing

# exec >/dev/kmsg 2>&1 </dev/console

Using the dracut shell

Dracut offers a shell for interactive debugging in the event dracut fails to locate your root filesystem. To enable the shell:

Add the boot parameter ''rd.shell'' to your bootloader configuration file (e.g. /etc/grub.conf)

Remove the boot arguments ''rhgb'' and ''quiet''

A sample /etc/grub.conf bootloader configuration file is listed below.

default=0
timeout=5
serial --unit=0 --speed=9600
terminal --timeout=5 serial console
title Fedora (2.6.29.5-191.fc11.x86_64)
  root (hd0,0)
  kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 rd.shell
  initrd /dracut-2.6.29.5-191.fc11.x86_64.img

If system boot fails, you will be dropped into a shell as seen in the example below.

No root device found
Dropping to debug shell.

sh: can't access tty; job control turned off

#

Use this shell prompt to gather the information requested above (see the section called “All bug reports”).

Accessing the root volume from the dracut shell

From the dracut debug shell, you can manually perform the task of locating and preparing your root volume for boot. The required steps will depend on how your root volume is configured. Common scenarios include:

A block device (e.g. /dev/sda7)
A LVM logical volume (e.g. /dev/VolGroup00/LogVol00)
An encrypted device (e.g. /dev/mapper/luks-4d5972ea-901c-4584-bd75-1da802417d83)
A network attached device (e.g. netroot=iscsi:@192.168.0.4::3260::iqn.2009-02.org.fedoraproject:for.all)

The exact method for locating and preparing will vary. However, to continue with a successful boot, the objective is to locate your root volume and create a symlink /dev/root which points to the file system. For example, the following example demonstrates accessing and booting a root volume that is an encrypted LVM Logical volume.

Inspect your partitions using parted

# parted /dev/sda -s p
Model: ATA HTS541060G9AT00 (scsi)
Disk /dev/sda: 60.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number  Start   End     Size    Type      File system  Flags
1      32.3kB  10.8GB  107MB   primary   ext4         boot
2      10.8GB  55.6GB  44.7GB  logical                lvm

You recall that your root volume was a LVM logical volume. Scan and activate any logical volumes.
```
# lvm vgscan
# lvm vgchange -ay
```

You should see any logical volumes now using the command blkid:

# blkid
/dev/sda1: UUID="3de247f3-5de4-4a44-afc5-1fe179750cf7" TYPE="ext4"
/dev/sda2: UUID="Ek4dQw-cOtq-5MJu-OGRF-xz5k-O2l8-wdDj0I" TYPE="LVM2_member"
/dev/mapper/linux-root: UUID="def0269e-424b-4752-acf3-1077bf96ad2c" TYPE="crypto_LUKS"
/dev/mapper/linux-home: UUID="c69127c1-f153-4ea2-b58e-4cbfa9257c5e" TYPE="ext3"
/dev/mapper/linux-swap: UUID="47b4d329-975c-4c08-b218-f9c9bf3635f1" TYPE="swap"

From the output above, you recall that your root volume exists on an encrypted block device. Following the guidance disk encryption guidance from the Installation Guide, you unlock your encrypted root volume.
```
# UUID=$(cryptsetup luksUUID /dev/mapper/linux-root)
# cryptsetup luksOpen /dev/mapper/linux-root luks-$UUID
Enter passphrase for /dev/mapper/linux-root:
Key slot 0 unlocked. 
```
Next, make a symbolic link to the unlocked root volume
```
# ln -s /dev/mapper/luks-$UUID /dev/root
```
With the root volume available, you may continue booting the system by exiting the dracut shell
```
# exit
```

Additional dracut boot parameters

For more debugging options, see the section called “Debug” in the man page dracut.kernel(7).

Chapter 3. Developer Manual

dracut Components

dracut uses a modular system to build and extend the initramfs image. All modules are located in /usr/share/dracut/modules.d or in <git-src>/modules.d. The most basic dracut module is 99base. In 99base the initial shell script init is defined, which gets run by the kernel after initramfs loading. Although you can replace init with your own version of 99base, this is not encouraged. Instead you should use, if possible, the hooks of dracut. All hooks, and the point of time in which they are executed, are described in the section called “Boot Process Stages”.

The main script, which creates the initramfs is dracut itsself. It parses all arguments and sets up the directory, in which everything is installed. It then executes all check, install, installkernel scripts found in the modules, which are to be processed. After everything is installed, the install directory is archived and compressed to the final initramfs image. All helper functions used by check, install and installkernel are found in in the file dracut-functions. These shell functions are available to all module installer (install, installkernel) scripts, without the need to source dracut-functions.

A module can check the preconditions for install and installkernel with the check script. Also dependencies can be expressed with check. If a module passed check, install and installkernel will be called to install all of the necessary files for the module. To split between kernel and non-kernel parts of the installation, all kernel module related parts have to be in installkernel. All other files found in a module directory are module specific and mostly are hook scripts and udev rules.

Boot Process Stages

The init script in 99base is the main script, which prepares the root file system for usage, runs udev, mounts the real root device, kills the remaining processes, and switches to the real root device for further booting. dracut modules can insert custom script at various points, to control the boot process. These hooks are plain directories containing shell scripts ending with ".sh", which are sourced by init. Common used functions are in dracut-lib.sh, which can be sourced by any script.

Basic Setup

The first thing init does, is to mount /proc and /sys and manually create the basic device nodes and symbolic links in /dev needed to execute basic commands. Then logging is setup according to kernel command line arguments. /dev/pts and /dev/shm are mounted and the first hook is sourced.

Hook: cmdline

The cmdline hook is a place to insert scripts to parse the kernel command line and prepare the later actions, like setting up udev rules and configuration files.

In this hook the most important environment variable is defined: root. The second one is rootok, which indicates, that a module claimed to be able to parse the root defined. So for example, root=iscsi:.... will be claimed by the iscsi dracut module, which then sets rootok.

Hook: pre-udev

This hook is executed right after the cmdline hook and a check if root and rootok were set. Here modules can take action with the final root, and before udev has been run.

Start Udev

Now udev is started and the logging for udev is setup.

Hook: pre-trigger

In this hook, you can set udev environment variables with udevadm control --property=KEY=value or control the further execution of udev with udevadm.

Trigger Udev

udev is triggered by calling udevadm trigger, which sends add events for all devices and subsystems.

Main Loop

Now the main loop of 99base/init begins. Here we loop until udev has settled and all scripts in initqueue/finished returned true. In this loop there are three hooks, where scripts can be inserted by calling /sbin/initqueue.

Initqueue

This hook gets executed every time a script is inserted here, regardless of the udev state.

Initqueue settled

This hooks gets executed every time udev has settled.

Initqueue timeout

This hooks gets executed, when the main loop counter becomes half of the rd.retry counter.

Initqueue finished

This hook is called after udev has settled and if all scripts herein return 0 the main loop will be ended.

Hook: pre-mount

Before the root device is mounted all scripts in the hook pre-mount are executed. In some cases (e.g. NFS) the real root device is already mounted, though.

Hook: mount

This hook is mainly to mount the real root device.

Hook: pre-pivot

This hook is the last hook and is called before init finally switches root to the real root device. This is a good place to clean up and kill processes not needed anymore.

Cleanup and switch_root

Init kills all udev processes, cleans up the environment, sets up the arguments for the real init process and finally calls switch_root. switch_root removes the whole filesystem hierarchy of the initramfs, chroot()s to the real root device and calls /sbin/init with the specified arguments.

To ensure all files in the initramfs hierarchy can be removed, all processes still running from the initramfs should not have any open file descriptors left.

Network Infrastructure

Writing a Module

A simple example module is 96insmodpost, which modprobes a kernel module after udev has settled and the basic device drivers have been loaded.

All module installation information is in the file module-setup.sh.

First we create a check() function, which just exits with 0 indicating that this module should be included by default.

check():

return 0

The we create the install() function, which installs a cmdline hook with priority number 20 called parse-insmodpost.sh. It also installs the insmodpost.sh script in /sbin.

install():

inst_hook cmdline 20 "$moddir/parse-insmodpost.sh"
inst_simple "$moddir/insmodpost.sh" /sbin/insmodpost.sh

The pase-instmodpost.sh parses the kernel command line for a argument rd.driver.post, blacklists the module from being autoloaded and installs the hook insmodpost.sh in the initqueue/settled.

parse-insmodpost.sh:

for p in $(getargs rd.driver.post=); do
    echo "blacklist $p" >> /etc/modprobe.d/initramfsblacklist.conf
    _do_insmodpost=1
done

[ -n "$_do_insmodpost" ] && /sbin/initqueue --settled --unique --onetime /sbin/insmodpost.sh
unset _do_insmodpost

insmodpost.sh, which is called in the initqueue/settled hook will just modprobe the kernel modules specified in all rd.driver.post kernel command line parameters. It runs after udev has settled and is only called once (--onetime).

insmodpost.sh:

. /lib/dracut-lib.sh

for p in $(getargs rd.driver.post=); do
    modprobe $p
done

check()

check() is called by dracut to evaluate the inclusion of a dracut module in the initramfs.

$hostonly: If the $hostonly variable is set, then the module check() function should be in "hostonly" mode, which means, that the check() should only return 0, if the module is really needed to boot this specific host.

check() should return with:

0: Include the dracut module in the initramfs.
1: Do not include the dracut module. The requirements are not fullfilled (missing tools, etc.)
255: Only include the dracut module, if another module requires it or if explicitly specified in the config file or on the argument list.

depends()

The function depends() should echo all other dracut module names the module depends on.

install()

dracut_install

inst

inst_hook

inst_rules

installkernel()

instmods

Creation Functions

Initramfs Functions

Network Modules

Appendix A. Man Pages

Table of Contents

dracut

dracut — create initial ramdisk images for preloading modules

dracut.conf

dracut.conf — configuration file(s) for dracut

dracut.kernel

dracut.kernel — dracut kernel command line options

dracut

Name

dracut — create initial ramdisk images for preloading modules

Synopsis

dracut [ OPTION ...] [ <image> [ <kernel-version> ] ]

Description

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.

For a complete list of kernel command line options see dracut.kernel(7)

Options

-f , --force: overwrite existing initramfs file.
-m , --modules <list of dracut modules>: specify a space-separated list of dracut modules to call when building the initramfs. Modules are located in /usr/share/dracut/modules.d. This parameter can be specified multiple times.
-o , --omit <list of dracut modules>: omit a space-separated list of dracut modules. This parameter can be specified multiple times.
-a , --add <list of dracut modules>: add a space-separated list of dracut modules to the default set of modules. This parameter can be specified multiple times.
--force-add <list of dracut modules>: force to add a space-separated list of dracut modules to the default set of modules, when -H is specified. This parameter can be specified multiple times.
-d , --drivers <list of kernel modules>: specify a space-separated list of kernel modules to exclusively include in the initramfs. The kernel modules have to be specified without the ".ko" suffix. This parameter can be specified multiple times.
--add-drivers <list of kernel modules>: specify a space-separated list of kernel modules to add to the initramfs. The kernel modules have to be specified without the ".ko" suffix. This parameter can be specified multiple times.
--filesystems <list of filesystems>: specify a space-separated list of kernel filesystem modules to exclusively include in the generic initramfs. This parameter can be specified multiple times.
-k , --kmoddir <kernel directory>: specify the directory, where to look for kernel modules
--fwdir <dir>[:<dir>...]: specify additional directories, where to look for firmwares. This parameter can be specified multiple times.
--kernel-only: only install kernel drivers and firmware files
--no-kernel: do not install kernel drivers and firmware files
--mdadmconf: include local /etc/mdadm.conf
--nomdadmconf: do not include local /etc/mdadm.conf
--lvmconf: include local /etc/lvm/lvm.conf
--nolvmconf: do not include local /etc/lvm/lvm.conf
--fscks [LIST]: add a space-separated list of fsck tools, in addition to dracut.conf's specification; the installation is opportunistic (non-existing tools are ignored)
--nofscks: inhibit installation of any fsck tools
--strip: strip binaries in the initramfs (default)
--nostrip: do not strip binaries in the initramfs
--prefix <dir>: prefix initramfs files with the specified directory
--noprefix: do not prefix initramfs files (default)
-h , --help: display help text and exit.
--debug: output debug information of the build process
-v , --verbose: increase verbosity level (default is info(4))
-q , --quiet: decrease verbosity level (default is info(4))
-c , --conf <dracut configuration file>: specify configuration file to use. Default: /etc/dracut.conf
--confdir <configuration directory>: specify configuration directory to use. Default: /etc/dracut.conf.d
-l , --local: activates the local mode. dracut will use modules from the current working directory instead of the system-wide installed modules in /usr/share/dracut/modules.d. This is useful when running dracut from a git checkout.
-H , --hostonly: Host-Only mode: Install only what is needed for booting the local host instead of a generic host.
Warning
If chrooted to another root other than the real root device, use "--fstab" and provide a valid /etc/fstab.
--fstab: Use /etc/fstab instead of /proc/self/mountinfo.
--add_fstab; <filename>: Add entries of <filename> to the initramfs /etc/fstab.
--mount; "<device> <mountpoint> <filesystem type> <filesystem options>": Add entries of <filename> to the initramfs /etc/fstab.
-i , --include <SOURCE> <TARGET>: include the files in the SOURCE directory into the TARGET directory in the final initramfs. If SOURCE is a file, it will be installed to TARGET in the final initramfs. This parameter can be specified multiple times.
-I , --install <file list>: install the space separated list of files into the initramfs.
--gzip: Compress the generated initramfs using gzip. This will be done by default, unless another compression option or --no-compress is passed. Equivalent to "--compress=gzip -9"
--bzip2: Compress the generated initramfs using bzip2.
Warning
Make sure your kernel has bzip2 decompression support compiled in, otherwise you will not be able to boot. Equivalent to "--compress=bzip2"
--lzma: Compress the generated initramfs using lzma.
Warning
Make sure your kernel has lzma decompression support compiled in, otherwise you will not be able to boot. Equivalent to "--compress=lzma -9"
--xz: Compress the generated initramfs using xz.
Warning
Make sure your kernel has xz decompression support compiled in, otherwise you will not be able to boot. Equivalent to "--compress=xz --check=crc32 --lzma2=dict=1MiB"
--compress <compressor>: Compress the generated initramfs using the passed compression program. If you pass it just the name of a compression program, it will call that program with known-working arguments. If you pass a quoted string with arguments, it will be called with exactly those arguments. Depending on what you pass, this may result in an initramfs that the kernel cannot decompress.
--no-compress: Do not compress the generated initramfs. This will override any other compression options.
--list-modules: List all available dracut modules.
-M , --show-modules: Print included module's name to standard output during build.
--keep: Keep the initramfs temporary directory for debugging purposes.

Files

/var/log/dracut.log: logfile of initramfs image creation
/tmp/dracut.log: logfile of initramfs image creation, if /var/log/dracut.log is not writable
/etc/dracut.conf: see dracut.conf(5)
/etc/dracut.conf.d/*.conf: see dracut.conf(5)

Configuration in the Initramfs

/etc/conf.d/: Any files found in /etc/conf.d/ will be sourced in the initramfs to set initial values. Command line options will override these values set in the configuration files.
/etc/cmdline: Can contain additional command line options.

Availability

The dracut command is part of the dracut package and is available from https://dracut.wiki.kernel.org

dracut.conf

Name

dracut.conf — configuration file(s) for dracut

Synopsis

/etc/dracut.conf /etc/dracut.conf.d/*.conf

Description

dracut.conf is loaded during the initialisation phase of dracut. Command line parameter will overwrite any values set here. dracut.conf.d/*.conf files are read in alphanumerical order and will overwrite parameters set in /etc/dracut.conf. Each line specifies an attribute and a value. A '#' indicates the beginning of a comment; following characters, up to the end of the line are not interpreted.

dracutmodules+=" <dracut modules> "

Specify a space-separated list of dracut modules to call when building the initramfs. Modules are located in /usr/share/dracut/modules.d.

omit_dracutmodules+=" <dracut modules> "

Omit a space-separated list of dracut modules.

add_dracutmodules+=" <dracut modules> "

Add a space-separated list of dracut modules.

drivers+=" <kernel modules> "

Specify a space-separated list of kernel modules to exclusively include in the initramfs. The kernel modules have to be specified without the ".ko" suffix.

add_drivers+=" <kernel modules> "

Specify a space-separated list of kernel modules to add to the initramfs. The kernel modules have to be specified without the ".ko" suffix.

filesystems+=" <filesystem names> "

Specify a space-separated list of kernel filesystem modules to exclusively include in the generic initramfs.

drivers_dir="<kernel modules directory>"

Specify the directory, where to look for kernel modules

fw_dir+=" :<dir>[:<dir> ...] "

Specify additional directories, where to look for firmwares, separated by :

install_items+=" <file>[ <file> ...] "

Specify additional files to include in the initramfs, separated by spaces.

do_strip="{yes|no}"

Strip binaries in the initramfs (default=yes)

hostonly="{yes|no}"

Host-Only mode: Install only what is needed for booting the local host instead of a generic host.

Warning

If chrooted to another root other than the real root device, use --fstab and provide a valid /etc/fstab.

use_fstab="{yes|no}"

Use /etc/fstab instead of /proc/self/mountinfo.

add_fstab+=" <filename> "

Add entries of <filename> to the initramfs /etc/fstab.

mdadmconf="{yes|no}"

Include local /etc/mdadm.conf (default=yes)

lvmconf="{yes|no}"

Include local /etc/lvm/lvm.conf (default=yes)

fscks=" <fsck tools> "

Add a space-separated list of fsck tools. If nothing is specified, the default is: "umount mount /sbin/fsck* xfs_db xfs_check xfs_repair e2fsck jfs_fsck reiserfsck btrfsck"

The installation is opportunistic (non-existing tools are ignored).

nofscks="{yes}"

If specified, inhibit installation of any fsck tools.

kernel_only="{yes|no}"

Only install kernel drivers and firmware files. (default=no)

no_kernel="{yes|no}"

Do not install kernel drivers and firmware files (default=no)

stdloglvl="{0-6}"

Set logging to standard error level.

sysloglvl="{0-6}"

Set logging to syslog level.

fileloglvl="{0-6}"

Set logging to file level.

logfile="<file>"

Path to log file.

show_modules="{yes|no}"

Print included module's name to standard output during build.

Files

/etc/dracut/conf.d/: Any /etc/dracut/conf.d/*.conf file can overwrite the values in /etc/dracut.conf. The configuration files are read in alphanumerical order.

dracut.kernel

Name

dracut.kernel — dracut kernel command line options

Description

The root filesystem used by the kernel is specified in the boot configuration file, as always. The traditional root=/dev/hda1 style device specification is allowed. If a label is used, as in root=LABEL=rootPart the initramfs will search all available devices for an ext2 or ext3 filesystem with the appropriate label, and mount that device as the root filesystem. root=UUID=uuidnumber will mount the partition with that UUID as the root filesystem.

Standard

init=<path to real init>

root=<path to blockdevice>

specify blockdevice to use as root filesystem. e.g.:

root=/dev/sda1
root=/dev/disk/by-path/pci-0000:00:1f.1-scsi-0:0:1:0-part1

rootfstype=<filesystem type>

"auto" if not specified, e.g.:

rootfstype=ext3

rootflags=<mount options>

specify additional mount options for the root filesystem. If not set, /etc/fstab of the real root will be parsed for special mount options and mounted accordingly.

rd.fstab=0

do not honor special mount options for the root filesystem found in /etc/fstab of the real root.

Misc

rd.driver.blacklist=<drivername>[,<drivername>,...]: do not load kernel module <drivername>. This parameter can be specified multiple times.
rd.driver.pre=<drivername>[,<drivername>,...]: force loading kernel module <drivername>. This parameter can be specified multiple times.
rd.driver.post=<drivername>[,<drivername>,...]: force loading kernel module <drivername> after all automatic loading modules have been loaded. This parameter can be specified multiple times.

Debug

rd.info: print informational output though "quiet" is set
rd.shell: allow dropping to a shell, if root mounting fails
rd.debug: set -x for the dracut shell and logs to dmesg, console and /run/initramfs/init.log
rd.break: drop to a shell at the end
rd.break={cmdline|pre-udev|pre-trigger|initqueue|pre-mount|mount|pre-pivot}: drop to a shell on defined breakpoint
rd.udev.info: set udev to loglevel info
rd.udev.debug: set udev to loglevel debug

I18N

vconsole.keymap= <keymap base file name>

keyboard translation table loaded by loadkeys; taken from keymaps directory; will be written as KEYMAP to /etc/vconsole.conf in the initramfs, e.g.:

vconsole.keymap=de-latin1-nodeadkeys

vconsole.keymap.ext=<list of keymap base file names>

list of extra keymaps to bo loaded (sep. by space); will be written as EXT_KEYMAP to /etc/vconsole.conf in the initramfs

vconsole.unicode=<1|0>

boolean, indicating UTF-8 mode; will be written as UNICODE to /etc/vconsole.conf in the initramfs

vconsole.font=<font base file name>

console font; taken from consolefonts directory; will be written as FONT to /etc/vconsole.conf in the initramfs; e.g.:

vconsole.font=LatArCyrHeb-16

vconsole.font.map=<console map base file name>

see description of '-m' parameter in setfont manual; taken from consoletrans directory; will be written as FONT_MAP to /etc/vconsole.conf in the initramfs

vconsole.font.unimap=<unicode table base file name>

see description of '-u' parameter in setfont manual; taken from unimaps directory; will be written as FONT_UNIMAP to /etc/vconsole.conf in the initramfs

locale.LANG=<locale>

taken from the environment; if no UNICODE is defined we set its value in basis of LANG value (whether it ends with ".utf8" (or similar) or not); will be written as LANG to /etc/locale.conf in the initramfs; e.g.:

locale.LANG=pl_PL.utf8

locale.LC_ALL=<locale>

taken from the environment; will be written as LC_ALL to /etc/locale.conf in the initramfs

LVM

rd.lvm=0: disable LVM detection
rd.lvm.vg=<volume group name>: only activate the volume groups with the given name rd.lvm.vg can be specified multiple times on the kernel command line.
rd.lvm.lv=<logical volume name>: only activate the logical volumes with the given name rd.lvm.lv can be specified multiple times on the kernel command line.
rd.lvm.conf=0: remove any /etc/lvm/lvm.conf, which may exist in the initramfs

crypto LUKS

rd.luks=0: disable crypto LUKS detection
rd.luks.uuid=<luks uuid>: only activate the LUKS partitions with the given UUID Any "luks-" of the LUKS UUID is removed before comparing to <luks uuid>. The comparisons also matches, if <luks uuid> is only the beginning of the LUKS UUID, so you don't have to specify the full UUID. This parameter can be specified multiple times.
rd.luks.crypttab=0: do not check, if LUKS partition is in /etc/crypttab

crypto LUKS - key on removable device support

rd.luks.key=<keypath>:<keydev>:<luksdev>

keypath is a path to key file to look for. It's REQUIRED. When keypath ends with '.gpg' it's considered to be key encrypted symmetrically with GPG. You will be prompted for password on boot. GPG support comes with 'crypt-gpg' module which needs to be added explicitly.

keydev is a device on which key file resides. It might be kernel name of devices (should start with "/dev/"), UUID (prefixed with "UUID=") or label (prefix with "LABEL="). You don't have to specify full UUID. Just its beginning will suffice, even if its ambiguous. All matching devices will be probed. This parameter is recommended, but not required. If not present, all block devices will be probed, which may significantly increase boot time.

If luksdev is given, the specified key will only be applied for that LUKS device. Possible values are the same as for keydev. Unless you have several LUKS devices, you don't have to specify this parameter.

The simplest usage is:

rd.luks.key=/foo/bar.key

As you see, you can skip colons in such case.

MD

rd.md=0: disable MD RAID detection
rd.md.imsm=0: disable MD RAID for imsm/isw raids, use DM RAID instead
rd.md.ddf=0: disable MD RAID for SNIA ddf raids, use DM RAID instead
rd.md.conf=0: ignore mdadm.conf included in initramfs
rd.md.uuid=<md raid uuid>: only activate the raid sets with the given UUID. This parameter can be specified multiple times.

DM RAID

rd.dm=0: disable DM RAID detection
rd.dm.uuid=<dm raid uuid>: only activate the raid sets with the given UUID. This parameter can be specified multiple times.

FIPS

rd.fips

enable FIPS

boot=<boot device>

specify the device, where /boot is located.

e.g.
  boot=/dev/sda1
  boot=/dev/disk/by-path/pci-0000:00:1f.1-scsi-0:0:1:0-part1
  boot=UUID=<uuid>
  boot=LABEL=<label>

rd.fips.skipkernel

skip checksum check of the kernel image. Useful, if the kernel image is not in a separate boot partition.

Network

ip={dhcp|on|any|dhcp6|auto6|ibft}

dhcp|on|any: get ip from dhcp server from all interfaces. If root=dhcp, loop sequentially through all interfaces (eth0, eth1, ...) and use the first with a valid DHCP root-path.

auto6: IPv6 autoconfiguration

dhcp6: IPv6 DHCP

ibft: iBFT autoconfiguration

ip=<interface>:{dhcp|on|any|dhcp6|auto6}

dhcp|on|any|dhcp6: get ip from dhcp server on a specific interface

auto6: do IPv6 autoconfiguration

This parameter can be specified multiple times.

ip=<client-IP>:[ <server-id> ]:<gateway-IP>:<netmask>:<client_hostname>:<interface>:{none|off}

explicit network configuration. If you want do define a IPv6 address, put it in brackets (e.g. [2001:DB8::1]). This parameter can be specified multiple times.

ifname=<interface>:<MAC>

Assign network device name <interface> (ie eth0) to the NIC with MAC <MAC>. Note letters in the MAC-address must be lowercase! Note: If you use this option you must specify an ifname= argument for all interfaces used in ip= or fcoe= arguments. This parameter can be specified multiple times.

bootdev=<interface>

specify network interface to use routing and netroot information from. Required if multiple ip= lines are used.

nameserver=<IP>[nameserver=<IP> ...]

specify nameserver(s) to use

biosdevname={0|1}

turn on/off biosdevname network interface renaming

NFS

root=[<server-ip>:]<root-dir>[:<nfs-options>]: mount nfs share from <server-ip>:/<root-dir>, if no server-ip is given, use dhcp next_server. if server-ip is an IPv6 address it has to be put in brackets, e.g. [2001:DB8::1]. NFS options can be appended with the prefix ":" or "," and are seperated by ",".
root=nfs:[<server-ip>:]<root-dir>[:<nfs-options>], root=nfs4:[<server-ip>:]<root-dir>[:<nfs-options>], root={dhcp|dhcp6}: root=dhcp alone directs initrd to look at the DHCP root-path where NFS options can be specified. root-path=<server-ip>:<root-dir>[,<nfs-options>] root-path=nfs:<server-ip>:<root-dir>[,<nfs-options>] root-path=nfs4:<server-ip>:<root-dir>[,<nfs-options>]
root=/dev/nfs nfsroot=[<server-ip>:]<root-dir>[:<nfs-options>]: Deprecated! kernel Documentation/filesystems/nfsroot.txt defines this method. This is supported by dracut, but not recommended.
rd.nfs.domain= <NFSv4 domain name>: Set the NFSv4 domain name. Will overwrite the settings in /etc/idmap.conf.

iSCSI

root=iscsi:[<username>:<password>[:<reverse>:<password>]@][ <servername> ]:[ <protocol> ]:[ <port> ]:[ <LUN> ]:<targetname>

protocol defaults to "6", LUN defaults to "0".

If the "servername" field is provided by BOOTP or DHCP, then that field is used in conjunction with other associated fields to contact the boot server in the Boot stage. However, if the "servername" field is not provided, then the "targetname" field is then used in the Discovery Service stage in conjunction with other associated fields.

See http://tools.ietf.org/html/rfc4173.

e.g.:

root=iscsi:192.168.50.1::::iqn.2009-06.dracut:target0

If servername is an IPv6 address, it has to be put in brackets. e.g.:

root=iscsi:[2001:DB8::1]::::iqn.2009-06.dracut:target0

root=??? netroot=iscsi:[<username>:<password>[:<reverse>:<password>]@][ <servername> ]:[ <protocol> ]:[ <port> ]:[ <LUN> ]:<targetname> ...

multiple netroot options allow setting up multiple iscsi disks. e.g.:

root=UUID=12424547
netroot=iscsi:192.168.50.1::::iqn.2009-06.dracut:target0
netroot=iscsi:192.168.50.1::::iqn.2009-06.dracut:target1

If servername is an IPv6 address, it has to be put in brackets. e.g.:

netroot=iscsi:[2001:DB8::1]::::iqn.2009-06.dracut:target0

root=??? rd.iscsi.initiator=<initiator> rd.iscsi.target.name=<target name> rd.iscsi.target.ip=<target ip> rd.iscsi.target.port=<target port> rd.iscsi.target.group=<target group> rd.iscsi.username=<username> rd.iscsi.password=<password> rd.iscsi.in.username=<in username> rd.iscsi.in.password=<in password>

manually specify all iscsistart parameter (see iscsistart --help)

root=??? netroot=iscsi rd.iscsi.firmware=1

will read the iscsi parameter from the BIOS firmware

FCoE

fcoe=<edd|interface|MAC>:{dcb|nodcb}: Try to connect to a FCoE SAN through the NIC specified by <interface> or <MAC> or EDD settings. For the second argument, currently only nodcb is supported. This parameter can be specified multiple times. Note: letters in the MAC-address must be lowercase!

NBD

root=nbd:<server>:<port>[:<fstype>][:<mountopts>]: mount nbd share from <server>
root=dhcp: with dhcp root-path=nbd:<server>:<port>[:<fstype>][:<mountopts>] root=dhcp alone directs initrd to look at the DHCP root-path where NBD options can be specified. This syntax is only usable in cases where you are directly mounting the volume as the rootfs.

DASD

rd.dasd_mod.dasd=....: same syntax as the kernel module parameter (s390 only)
rd.dasd=<dasd_adaptor device bus ID>[,readonly=X][,use_diag=X][,erplog=X]: activate DASD device with the given adaptor device bus ID and setting the sysfs attributes to the specified values This parameter can be specified multiple times.

ZFCP

rd.zfcp=<zfcp adaptor device bus ID>,<WWPN>,<FCPLUN>

rd.zfcp can be specified multiple times on the kernel command line. e.g.:

rd.zfcp=0.0.4000,0x5005076300C213e9,0x5022000000000000

rd.zfcp.conf

ignore zfcp.conf included in the initramfs

ZNET

rd.znet=<nettype>,<subchannels>,<options>

rd.znet can be specified multiple times on the kernel command line. e.g.:

rd.znet=qeth,0.0.0600,0.0.0601,0.0.0602,layer2=1,portname=foo
rd.znet=ctc,0.0.0600,0.0.0601,0.0.0602,protocol=bar

Plymouth Boot Splash

plymouth.enable=0: disable the plymouth bootsplash.
rd.plymouth=0: disable the plymouth bootsplash only for the initramfs.

Kernel keys

masterkey=<kernel master key path name>

Set the path name of the kernel master key. e.g.:

masterkey=/etc/keys/kmk-trusted.blob

masterkeytype=<kernel master key type>

Set the type of the kernel master key. e.g.:

masterkeytype=trusted

evmkey=<EVM key path name>

Set the path name of the EVM key. e.g.:

evmkey=/etc/keys/evm-trusted.blob

ecryptfskey=<eCryptfs key path name>

Set the path name of the eCryptfs key. e.g.:

ecryptfskey=/etc/keys/ecryptfs-trusted.blob

Deprecated, renamed Options

Here is a list of options, which were used in dracut prior to version 008, and their new replacement.

rdbreak: rd.break
rd_CCW: rd.ccw
rd_DASD_MOD: rd.dasd_mod.dasd
rd_DASD: rd.dasd
rdinitdebug rdnetdebug: rd.debug
rd_NO_DM: rd.dm=0
rd_DM_UUID: rd.dm.uuid
rdblacklist: rd.driver.blacklist
rdinsmodpost: rd.driver.post
rdloaddriver: rd.driver.pre
rd_NO_FSTAB: rd.fstab=0
rdinfo: rd.info
check: rd.live.check
rdlivedebug: rd.live.debug
live_dir: rd.live.dir
liveimg: rd.live.image
overlay: rd.live.overlay
readonly_overlay: rd.live.overlay.readonly
reset_overlay: rd.live.overlay.reset
live_ram: rd.live.ram
rd_NO_CRYPTTAB: rd.luks.crypttab=0
rd_LUKS_KEYDEV_UUID: rd.luks.keydev.uuid
rd_LUKS_KEYPATH: rd.luks.keypath
rd_NO_LUKS: rd.luks=0
rd_LUKS_UUID: rd.luks.uuid
rd_NO_LVMCONF: rd.lvm.conf
rd_LVM_LV: rd.lvm.lv
rd_NO_LVM: rd.lvm=0
rd_LVM_SNAPSHOT: rd.lvm.snapshot
rd_LVM_SNAPSIZE: rd.lvm.snapsize
rd_LVM_VG: rd.lvm.vg
rd_NO_MDADMCONF: rd.md.conf=0
rd_NO_MDIMSM: rd.md.imsm=0
rd_NO_MD: rd.md=0
rd_MD_UUID: rd.md.uuid
rd_NFS_DOMAIN: rd.nfs.domain
iscsi_initiator: rd.iscsi.initiator
iscsi_target_name: rd.iscsi.target.name
iscsi_target_ip: rd.iscsi.target.ip
iscsi_target_port: rd.iscsi.target.port
iscsi_target_group: rd.iscsi.target.group
iscsi_username: rd.iscsi.username
iscsi_password: rd.iscsi.password
iscsi_in_username: rd.iscsi.in.username
iscsi_in_password: rd.iscsi.in.password
iscsi_firmware: rd.iscsi.firmware=0
rd_NO_PLYMOUTH: rd.plymouth=0
rd_retry: rd.retry
rdshell: rd.shell
rd_NO_SPLASH: rd.splash
rdudevdebug: rd.udev.debug
rdudevinfo: rd.udev.info
rd_NO_ZFCPCONF: rd.zfcp.conf=0
rd_ZFCP: rd.zfcp
rd_ZNET: rd.znet
KEYMAP: vconsole.keymap
KEYTABLE: vconsole.keymap
SYSFONT: vconsole.font
CONTRANS: vconsole.font.map
UNIMAP: vconsole.font.unimap
UNICODE: vconsole.unicode
EXT_KEYMAP: vconsole.keymap.ext

Configuration in the Initramfs

/etc/conf.d/: Any files found in /etc/conf.d/ will be sourced in the initramfs to set initial values. Command line options will override these values set in the configuration files.
/etc/cmdline: Can contain additional command line options.
/etc/cmdline.d/*.conf: Can contain additional command line options.

dracut

Harald Hoyer

Chapter 1. Introduction

Definition

Rationale

Implementation

Mount preparations

Chapter 2. User Manual

Creating an initramfs Image

Inspecting the Contents

Adding dracut Modules

Omitting dracut Modules

Adding Kernel Modules

Boot parameters

Specifying the root Device

Keyboard Settings

Blacklisting Kernel Modules

Speeding up the Boot Process

Injecting custom Files

Network Boot

Reducing the Image Size

NFS Root Device

iSCSI Root Device

FCoE Root Device

Troubleshooting

Identifying your problem area

Information to include in your report

All bug reports

Logical Volume Management related problems

Software RAID related problems

Network root device related problems

Debugging dracut

Configure a serial console

Redirecting non-interactive output

Using the dracut shell

Accessing the root volume from the dracut shell

Additional dracut boot parameters

Chapter 3. Developer Manual

dracut Components

Boot Process Stages

Basic Setup

Hook: cmdline

Hook: pre-udev

Start Udev

Hook: pre-trigger

Trigger Udev

Main Loop

Initqueue

Initqueue settled

Initqueue timeout

Initqueue finished

Hook: pre-mount

Hook: mount

Hook: pre-pivot

Cleanup and switch_root

Network Infrastructure

Writing a Module

check()

depends()

install()

installkernel()

Creation Functions

Initramfs Functions

Network Modules

Appendix A. Man Pages

dracut

Name

Synopsis

Description

Options

Warning

Warning

Warning

Warning

Files

Configuration in the Initramfs

Availability

See Also

dracut.conf

Name