dracut

Harald Hoyer

Revision History
Revision 3.0October 2013HH

Table of Contents

I. Introduction
1. Definition
2. Rationale
3. Implementation
4. Mount preparations
5. Dracut on shutdown
II. User Manual
6. DRACUT(8)
NAME
SYNOPSIS
DESCRIPTION
USAGE
Inspecting the Contents
Adding dracut Modules
Omitting dracut Modules
Adding Kernel Modules
Boot parameters
Injecting custom Files
Network Boot
Troubleshooting
Identifying your problem area
Information to include in your report
Debugging dracut
OPTIONS
FILES
Configuration in the initramfs
AVAILABILITY
AUTHORS
SEE ALSO
7. DRACUT.CONF(5)
NAME
SYNOPSIS
Description
Files
AUTHOR
See Also
8. DRACUT.CMDLINE(7)
NAME
DESCRIPTION
Standard
iso-scan/filename
Misc
Debug
I18N
LVM
crypto LUKS
crypto LUKS - key on removable device support
MD RAID
DM RAID
MULTIPATH
FIPS
Network
NFS
CIFS
iSCSI
FCoE
NBD
DASD
ZFCP
ZNET
Booting live images
Plymouth Boot Splash
Kernel keys
Deprecated, renamed Options
Configuration in the Initramfs
AUTHOR
SEE ALSO
9. LSINITRD(1)
NAME
SYNOPSIS
DESCRIPTION
OPTIONS
AVAILABILITY
AUTHORS
SEE ALSO
10. MKINITRD(8)
NAME
SYNOPSIS
DESCRIPTION
OPTIONS
AVAILABILITY
AUTHORS
SEE ALSO
11. Developer Manual
12. DRACUT.MODULES(7)
NAME
DESCRIPTION
Boot Process Stages
Hook: cmdline
Hook: pre-udev
Start Udev
Hook: pre-trigger
Trigger Udev
Main Loop
Hook: pre-mount
Hook: mount
Hook: pre-pivot
Hook: cleanup
Cleanup and switch_root
Network Infrastructure
Writing a Module
module-setup.sh: check()
module-setup.sh: depends()
module-setup.sh: cmdline()
module-setup.sh: install()
module-setup.sh: installkernel()
Creation Functions
Initramfs Functions
Network Modules
AUTHOR
SEE ALSO
13. DRACUT.BOOTUP(7)
NAME
DESCRIPTION
AUTHOR
SEE ALSO
A. License

Part I. 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.

Chapter 1. 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.

Chapter 2. 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.

Chapter 3. 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.

Chapter 4. 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.

If the systemd module is used in the initramfs, the ordering of the services started looks like Chapter 13, DRACUT.BOOTUP(7).

Chapter 5. Dracut on shutdown

On a systemd driven system, the dracut initramfs is also used for the shutdown procedure.

The following steps are executed during a shutdown:

  • systemd switches to the shutdown.target
  • systemd starts /lib/systemd/system/shutdown.target.wants/dracut-shutdown.service
  • dracut-shutdown.service executes /usr/lib/dracut/dracut-initramfs-restore which unpacks the initramfs to /run/initramfs
  • systemd finishes shutdown.target
  • systemd kills all processes
  • systemd tries to unmount everything and mounts the remaining read-only
  • systemd checks, if there is a /run/initramfs/shutdown executable
  • if yes, it does a pivot_root to /run/initramfs and executes ./shutdown. The old root is then mounted on /oldroot. /usr/lib/dracut/modules.d/99shutdown/shutdown.sh is the shutdown executable.
  • shutdown will try to umount every /oldroot mount and calls the various shutdown hooks from the dracut modules

This ensures, that all devices are disassembled and unmounted cleanly.

Part II. User Manual

Chapter 6. DRACUT(8)

NAME

dracut - low-level tool for generating an initramfs/initrd image

SYNOPSIS

dracut [OPTION…] [<image> [<kernel version>]]

DESCRIPTION

Create an initramfs <image> for the kernel with the version <kernel version>. If <kernel version> is omitted, then the version of the actual running kernel is used. If <image> is omitted or empty, then the default location /boot/initramfs-<kernel version>.img is used.

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, mounting the root filesystem and booting into the real system.

At boot time, the kernel unpacks that archive into RAM disk, mounts and uses it as initial root file system. All finding of the root device happens in this early userspace.

Initramfs images are also called "initrd".

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

If you are dropped to an emergency shell, while booting your initramfs, the file /run/initramfs/rdsosreport.txt is created, which can be saved to a (to be mounted by hand) partition (usually /boot) or a USB stick. Additional debugging info can be produced by adding rd.debug to the kernel command line. /run/initramfs/rdsosreport.txt contains all logs and the output of some tools. It should be attached to any report about dracut problems.

USAGE

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 --kver 2.6.40-1.rc5.f20

If you want to create lighter, smaller initramfs images, you may want to specify the --hostonly 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 --hostonly 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 | less

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

# lsinitrd -f /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 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

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 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 dracut.conf(5)):

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

Boot parameters

An initramfs generated without the "hostonly" mode, 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 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 dracut.cmdline(5).

To get a quick start for the suitable kernel command line on your system, use the --print-cmdline option:

# dracut --print-cmdline
 root=UUID=8b8b6f91-95c7-4da2-831b-171e12179081 rootflags=rw,relatime,discard,data=ordered rootfstype=ext4

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

or

root=LABEL=myrootpartitionlabel

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

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

or

# 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:

rd.vconsole.font=latarcyrheb-sun16 rd.vconsole.keymap=de-latin1-nodeadkeys rd.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.

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.driver.blacklist=mptsas rd.driver.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

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.d/mycmdline.conf initramfs-cmdline-pre.img

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

# mkdir -p rd.live.overlay/etc/cmdline.d
# mkdir -p rd.live.overlay/etc/conf.d
# echo "ip=dhcp" >> rd.live.overlay/etc/cmdline.d/mycmdline.conf
# echo export FOO=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
# echo export BAR=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
# tree rd.live.overlay/
rd.live.overlay/
`-- etc
    |-- cmdline.d
    |   `-- mycmdline.conf
    `-- 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.

If you specify ip=dhcp 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.d/mycmdline.conf, 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.

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: https://www.kernel.org/pub/linux/utils/boot/dracut/dracut.html

Identifying your problem area

  1. Remove 'rhgb' and 'quiet' from the kernel command line
  2. Add 'rd.shell' to the kernel command line. This will present a shell should dracut be unable to locate your root device
  3. Add 'rd.shell rd.debug log_buf_len=1M' to the kernel command line so that dracut shell commands are printed as they are executed
  4. The file /run/initramfs/rdsosreport.txt is generated, which contains all the logs and the output of all significant tools, which are mentioned later.

If you want to save that output, simply mount /boot by hand or insert an USB stick and mount that. Then you can store the output for later inspection.

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. /boot/grub2/grub.cfg) 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.
  • Turn on dracut debugging (see the debugging dracut section), and attach the file /run/initramfs/rdsosreport.txt.
  • If you use a dracut configuration file, please include /etc/dracut.conf and all files in /etc/dracut.conf.d/*.conf

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.

  1. First, enable serial console output for both the kernel and the bootloader.
  2. Open the file /boot/grub2/grub.cfg for editing. Below the line 'timeout=5', add the following:

    serial --unit=0 --speed=9600
    terminal --timeout=5 serial console
  3. Also in /boot/grub2/grub.cfg, add the following boot arguemnts to the 'kernel' line:

    console=tty0 console=ttyS0,9600
  4. When finished, the /boot/grub2/grub.cfg 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
  5. 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.
  6. Redirecting non-interactive output

    Note

    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:

  1. Add the boot parameter 'rd.shell' to your bootloader configuration file (e.g. /boot/grub2/grub.cfg)
  2. Remove the boot arguments 'rhgb' and 'quiet'

    A sample /boot/grub2/grub.cfg 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
  3. 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.
    
    #
  4. 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.example: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.

  1. 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
  2. You recall that your root volume was a LVM logical volume. Scan and activate any logical volumes.

    # lvm vgscan
    # lvm vgchange -ay
  3. 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"
  4. 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.
  5. Next, make a symbolic link to the unlocked root volume

    # ln -s /dev/mapper/luks-$UUID /dev/root
  6. 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 dracut.cmdline(7).

Debugging dracut on shutdown

To debug the shutdown sequence on systemd systems, you can rd.break on pre-shutdown or shutdown.

To do this from an already booted system:

# mkdir -p /run/initramfs/etc/cmdline.d
# echo "rd.debug rd.break=pre-shutdown rd.break=shutdown" > /run/initramfs/etc/cmdline.d/debug.conf
# touch /run/initramfs/.need_shutdown

This will give you a dracut shell after the system pivot’ed back in the initramfs.

OPTIONS

--kver <kernel version>
set the kernel version. This enables to specify the kernel version, without specifying the location of the initramfs image. For example:
# dracut --kver 3.5.0-0.rc7.git1.2.fc18.x86_64
-f, --force
overwrite existing initramfs file.
-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.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --add "module1 module2"  ...
--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.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --force-add "module1 module2"  ...
-o, --omit <list of dracut modules>

omit a space-separated list of dracut modules. This parameter can be specified multiple times.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --omit "module1 module2"  ...
-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/lib/dracut/modules.d. This parameter can be specified multiple times. This option forces dracut to only include the specified dracut modules. In most cases the "--add" option is what you want to use.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --modules "module1 module2"  ...
-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.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --drivers "kmodule1 kmodule2"  ...
--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.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --add-drivers "kmodule1 kmodule2"  ...
--force-drivers <list of kernel modules>

See add-drivers above. But in this case it is ensured that the drivers are tried to be loaded early via modprobe.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --force-drivers "kmodule1 kmodule2"  ...
--omit-drivers <list of kernel modules>

specify a space-separated list of kernel modules not to add to the initramfs. The kernel modules have to be specified without the ".ko" suffix. This parameter can be specified multiple times.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --omit-drivers "kmodule1 kmodule2"  ...
--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.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --filesystems "filesystem1 filesystem2"  ...
-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-cmdline <parameters>
specify default kernel command line parameters
--kernel-only
only install kernel drivers and firmware files
--no-kernel
do not install kernel drivers and firmware files
--early-microcode
Combine early microcode with ramdisk
--no-early-microcode
Do not combine early microcode with ramdisk
--print-cmdline
print the kernel command line for the current disk layout
--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)

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --fscks "fsck.foo barfsck"  ...
--nofscks
inhibit installation of any fsck tools
--strip
strip binaries in the initramfs (default)
--nostrip
do not strip binaries in the initramfs
--prelink
prelink binaries in the initramfs (default)
--noprelink
do not prelink binaries in the initramfs
--hardlink
hardlink files in the initramfs (default)
--nohardlink
do not hardlink files 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

--tmpdir <temporary directory>

specify temporary directory to use.

Default: /var/tmp

--sshkey <sshkey file>
ssh key file used with ssh-client module.
--logfile <logfile>

logfile to use; overrides any setting from the configuration files.

Default: /var/log/dracut.log

-l, --local
activates the local mode. dracut will use modules from the current working directory instead of the system-wide installed modules in /usr/lib/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 and generate host-specific configuration.

Warning

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

-N, --no-hostonly
Disable Host-Only mode

--hostonly-cmdline: Store kernel command line arguments needed in the initramfs

--no-hostonly-cmdline: Do not store kernel command line arguments needed in the initramfs

--persistent-policy <policy>
Use <policy> to address disks and partitions. <policy> can be any directory name found in /dev/disk. E.g. "by-uuid", "by-label"
--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> [<dump frequency> [<fsck order>]]]"
Mount <device> on <mountpoint> with <filesystem type> in the initramfs. <filesystem options>, <dump options> and <fsck order> can be specified, see fstab manpage for the details. The default <filesystem options> is "defaults". The default <dump frequency> is "0". the default <fsck order> is "2".
--mount "<mountpoint>"
Like above, but <device>, <filesystem type> and <filesystem options> are determined by looking at the current mounts.
--add-device <device>
Bring up <device> in initramfs, <device> should be the device name. This can be useful in hostonly mode for resume support when your swap is on LVM or an encrypted partition. [NB --device can be used for compatibility with earlier releases]
-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.

Note

If [LIST] has multiple arguments, then you have to put these in quotes. For example:

# dracut --install "/bin/foo /sbin/bar"  ...
--install-optional <file list>
install the space separated list of files into the initramfs, if they exist.
--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 "lzma --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 "lzma --compress=xz --check=crc32 --lzma2=dict=1MiB"

--lzo
Compress the generated initramfs using lzop.

Warning

Make sure your kernel has lzo decompression support compiled in, otherwise you will not be able to boot.

--lz4
Compress the generated initramfs using lz4.

Warning

Make sure your kernel has lz4 decompression support compiled in, otherwise you will not be able to boot.

--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.
--reproducible
Create reproducible images.
--no-reproducible
Do not create reproducible images.
--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.
--printsize
Print out the module install size

--profile: Output profile information of the build process

--ro-mnt: Mount / and /usr read-only by default.

-L, --stdlog <level>
[0-6] Specify logging level (to standard error)
          0 - suppress any messages
          1 - only fatal errors
          2 - all errors
          3 - warnings
          4 - info
          5 - debug info (here starts lots of output)
          6 - trace info (and even more)
--regenerate-all
Regenerate all initramfs images at the default location with the kernel versions found on the system. Additional parameters are passed through.
--loginstall <DIR>
Log all files installed from the host to <DIR>.
--uefi
Instead of creating an initramfs image, dracut will create an UEFI executable, which can be executed by an UEFI BIOS.
--uefi-stub <FILE>
Specifies the UEFI stub loader, which will load the attached kernel, initramfs and kernel command line and boots the kernel. The default is /lib/systemd/boot/efi/linux<EFI-MACHINE-TYPE-NAME>.efi.stub or /usr/lib/gummiboot/linux<EFI-MACHINE-TYPE-NAME>.efi.stub
--kernel-image <FILE>
Specifies the kernel image, which to include in the UEFI executable. The default is /lib/modules/<KERNEL-VERSION>/vmlinuz or /boot/vmlinuz-<KERNEL-VERSION>

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.conf5
/etc/dracut.conf.d/*.conf
see dracut.conf5
/usr/lib/dracut/dracut.conf.d/*.conf
see dracut.conf5

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. Deprecated, better use /etc/cmdline.d/*.conf.
/etc/cmdline.d/*.conf
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

AUTHORS

Harald Hoyer

Victor Lowther

Philippe Seewer

Warren Togami

Amadeusz Żołnowski

Jeremy Katz

David Dillow

Will Woods

SEE ALSO

dracut.cmdline(7) dracut.conf(5) lsinitrd(1)

Chapter 7. DRACUT.CONF(5)

NAME

dracut.conf - configuration file(s) for dracut

SYNOPSIS

/etc/dracut.conf /etc/dracut.conf.d/*.conf /usr/lib/dracut/dracut.conf.d/*.conf

Description

dracut.conf is loaded during the initialisation phase of dracut. Command line parameter will overwrite any values set here.

*.conf files are read from /usr/lib/dracut/dracut.conf.d and /etc/dracut.conf.d. Files with the same name in /etc/dracut.conf.d will replace files in /usr/lib/dracut/dracut.conf.d. The files are then 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.

dracut command line options will overwrite any values set here.

Configuration files must have the extension .conf; other extensions are ignored.

add_dracutmodules+=<dracut modules> "
Add a space-separated list of dracut modules to call when building the initramfs. Modules are located in /usr/lib/dracut/modules.d.
dracutmodules+=<dracut modules> "
Specify a space-separated list of dracut modules to call when building the initramfs. Modules are located in /usr/lib/dracut/modules.d. This option forces dracut to only include the specified dracut modules. In most cases the "add_dracutmodules" option is what you want to use.
omit_dracutmodules+=<dracut modules> "
Omit a space-separated list of dracut modules to call when building the initramfs. Modules are located in /usr/lib/dracut/modules.d.
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.
force_drivers+=<list of kernel modules> "
See add_drivers above. But in this case it is ensured that the drivers are tried to be loaded early via modprobe.
omit_drivers+=<kernel modules> "
Specify a space-separated list of kernel modules not 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.
install_optional_items+=<file>[ <file> …] "
Specify additional files to include in the initramfs, separated by spaces, if they exist.
compress="{bzip2|lzma|xz|gzip|lzo|lz4|<compressor [args …]>}"
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 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.
do_strip="{yes|no}"
Strip binaries in the initramfs (default=yes)
do_prelink="{yes|no}"
Prelink 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 and generate host-specific configuration.
hostonly_cmdline="{yes|no}"
If set, store the kernel command line arguments needed in the initramfs
persistent_policy="<policy>"
Use <policy> to address disks and partitions. <policy> can be any directory name found in /dev/disk. E.g. "by-uuid", "by-label"
tmpdir="<temporary directory>"
Specify temporary directory to use.

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.
add_device+=<device> "
Bring up <device> in initramfs, <device> should be the device name. This can be useful in hostonly mode for resume support when your swap is on LVM an encrypted partition.
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|no}"
If specified, inhibit installation of any fsck tools.
ro_mnt="{yes|no}"
Mount / and /usr read-only by default.
kernel_cmdline="parameters"
Specify default kernel command line parameters
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)
acpi_override="{yes|no}"
[WARNING] ONLY USE THIS IF YOU KNOW WHAT YOU ARE DOING! Override BIOS provided ACPI tables. For further documentation read Documentation/acpi/initrd_table_override.txt in the kernel sources. Search for ACPI table files (must have .aml suffix) in acpi_table_dir= directory (see below) and add them to a separate uncompressed cpio archive. This cpio archive gets glued (concatenated, uncompressed one must be the first one) to the compressed cpio archive. The first, uncompressed cpio archive is for data which the kernel must be able to access very early (and cannot make use of uncompress alogrithms yet) like microcode or ACPI tables (default=no).
acpi_table_dir="<dir>"
Directory to search for ACPI tables if acpi_override= is set to yes.
early_microcode="{yes|no}"
Combine early microcode with ramdisk (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 the name of the included modules to standard output during build.
*i18n_vars="<variable mapping>"
Distribution specific variable mapping. See dracut/modules.d/10i18n/README for a detailed description.
i18n_default_font="<fontname>"
The font <fontname> to install, if not specified otherwise. Default is "LatArCyrHeb-16".
i18n_install_all="{yes|no}"
Install everything regardless of generic or hostonly mode.
reproducible="{yes|no}"
Create reproducible images.
loginstall="<DIR>"
Log all files installed from the host to <DIR>.
uefi_stub="<FILE>"
Specifies the UEFI stub loader, which will load the attached kernel, initramfs and kernel command line and boots the kernel. The default is /lib/systemd/boot/efi/linux<EFI-MACHINE-TYPE-NAME>.efi.stub or /usr/lib/gummiboot/linux<EFI-MACHINE-TYPE-NAME>.efi.stub
kernel_image="<FILE>"
Specifies the kernel image, which to include in the UEFI executable. The default is /lib/modules/<KERNEL-VERSION>/vmlinuz or /boot/vmlinuz-<KERNEL-VERSION>

Files

/etc/dracut.conf
Old configuration file. You better use your own file in /etc/dracut.conf.d/.
/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.

AUTHOR

Harald Hoyer

See Also

dracut(8) dracut.cmdline(7)

Chapter 8. DRACUT.CMDLINE(7)

NAME

dracut.cmdline - dracut kernel command line options

DESCRIPTION

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

The traditional root=/dev/sda1 style device specification is allowed, but not encouraged. The root device should better be identified by LABEL or UUID. If a label is used, as in root=LABEL=<label_of_root> the initramfs will search all available devices for a 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.

In the following all kernel command line parameters, which are processed by dracut, are described.

"rd.*" parameters mentioned without "=" are boolean parameters. They can be turned on/off by setting them to {0|1}. If the assignment with "=" is missing "=1" is implied. For example rd.info can be turned off with rd.info=0 or turned on with rd.info=1 or rd.info. The last value in the kernel command line is the value, which is honored.

Standard

init=<path to real init>
specify the path to the init programm to be started after the initramfs has finished
root=<path to blockdevice>

specify the block device to use as the root filesystem.

Example. 

root=/dev/sda1
root=/dev/disk/by-path/pci-0000:00:1f.1-scsi-0:0:1:0-part1
root=/dev/disk/by-label/Root
root=LABEL=Root
root=/dev/disk/by-uuid/3f5ad593-4546-4a94-a374-bcfb68aa11f7
root=UUID=3f5ad593-4546-4a94-a374-bcfb68aa11f7
root=PARTUUID=3f5ad593-4546-4a94-a374-bcfb68aa11f7

rootfstype=<filesystem type>

"auto" if not specified.

Example. 

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.
ro
force mounting / and /usr (if it is a separate device) read-only. If none of ro and rw is present, both are mounted according to /etc/fstab.
rw
force mounting / and /usr (if it is a separate device) read-write. See also ro option.
rootfallback=<path to blockdevice>
specify the block device to use as the root filesystem, if the normal root cannot be found. This can only be a simple block device with a simple file system, for which the filesystem driver is either compiled in, or added manually to the initramfs. This parameter can be specified multiple times.
rd.auto rd.auto=1
enable autoassembly of special devices like cryptoLUKS, dmraid, mdraid or lvm. Default is off as of dracut version >= 024.
rd.hostonly=0
removes all compiled in configuration of the host system the initramfs image was built on. This helps booting, if any disk layout changed, especially in combination with rd.auto or other parameters specifying the layout.
rd.cmdline=ask
prompts the user for additional kernel command line parameters
rd.fstab=0
do not honor special mount options for the root filesystem found in /etc/fstab of the real root.
resume=<path to resume partition>

resume from a swap partition

Example. 

resume=/dev/disk/by-path/pci-0000:00:1f.1-scsi-0:0:1:0-part1
resume=/dev/disk/by-uuid/3f5ad593-4546-4a94-a374-bcfb68aa11f7
resume=UUID=3f5ad593-4546-4a94-a374-bcfb68aa11f7

rd.skipfsck
skip fsck for rootfs and /usr. If you’re mounting /usr read-only and the init system performs fsck before remount, you might want to use this option to avoid duplication.

iso-scan/filename

Using iso-scan/filename with a Fedora/Red Hat/CentOS Live iso should just work by copying the original kernel cmdline parameters.

Example. 

menuentry 'Live Fedora 20' --class fedora --class gnu-linux --class gnu --class os {
    set isolabel=Fedora-Live-LXDE-x86_64-20-1
    set isofile="/boot/iso/Fedora-Live-LXDE-x86_64-20-1.iso"
    loopback loop $isofile
    linux (loop)/isolinux/vmlinuz0 boot=isolinux iso-scan/filename=$isofile root=live:LABEL=$isolabel ro rd.live.image quiet rhgb
    initrd (loop)/isolinux/initrd0.img
}

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.
rd.retry=<seconds>
specify how long dracut should retry the initqueue to configure devices. The default is 30 seconds. After 2/3 of the time, degraded raids are force started. If you have hardware, which takes a very long time to announce its drives, you might want to extend this value.
rd.timeout=<seconds>
specify how long dracut should wait for devices to appear. The default is 0, which means forever. Note that this timeout should be longer than rd.retry to allow for proper configuration.
rd.noverifyssl
accept self-signed certificates for ssl downloads.
rd.ctty=<terminal device>
specify the controlling terminal for the console. This is useful, if you have multiple "console=" arguments.

Debug

If you are dropped to an emergency shell, the file /run/initramfs/rdsosreport.txt is created, which can be saved to a (to be mounted by hand) partition (usually /boot) or a USB stick. Additional debugging info can be produced by adding rd.debug to the kernel command line. /run/initramfs/rdsosreport.txt contains all logs and the output of some tools. It should be attached to any report about dracut problems.

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. If systemd is active in the initramfs, all output is logged to the systemd journal, which you can inspect with "journalctl -ab". If systemd is not active, the logs are written to dmesg and /run/initramfs/init.log. If "quiet" is set, it also logs to the console.
rd.memdebug=[0-3]

Print memory usage info at various points, set the verbose level from 0 to 3.

Higher level means more debugging output:
    0 - no output
    1 - partial /proc/meminfo
    2 - /proc/meminfo
    3 - /proc/meminfo + /proc/slabinfo
rd.break
drop to a shell at the end
rd.break={cmdline|pre-udev|pre-trigger|initqueue|pre-mount|mount|pre-pivot|cleanup}
drop to a shell on defined breakpoint
rd.udev.info
set udev to loglevel info
rd.udev.debug
set udev to loglevel debug

I18N

rd.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.

Example. 

rd.vconsole.keymap=de-latin1-nodeadkeys

rd.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
rd.vconsole.unicode
boolean, indicating UTF-8 mode; will be written as UNICODE to /etc/vconsole.conf in the initramfs
rd.vconsole.font=<font base file name>

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

Example. 

rd.vconsole.font=LatArCyrHeb-16

rd.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
rd.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
rd.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.

Example. 

rd.locale.LANG=pl_PL.utf8

rd.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.allow-discards=<luks uuid>
Allow using of discards (TRIM) requests for 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.allow-discards
Allow using of discards (TRIM) requests on all LUKS partitions.
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:

Example. 

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

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

Note

dracut pipes key to cryptsetup with -d - argument, therefore you need to pipe to crypsetup luksFormat with -d -, too!

Here follows example for key encrypted with GPG:

gpg --quiet --decrypt rootkey.gpg | \
cryptsetup -d - -v --cipher serpent-cbc-essiv:sha256 \
--key-size 256 luksFormat /dev/sda3

If you use plain keys, just add path to -d option:

cryptsetup -d rootkey.key -v --cipher serpent-cbc-essiv:sha256 \
 --key-size 256 luksFormat /dev/sda3

MD RAID

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.waitclean=1
wait for any resync, recovery, or reshape activity to finish before continuing
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.

MULTIPATH

rd.multipath=0
disable multipath detection

FIPS

rd.fips
enable FIPS
boot=<boot device>

specify the device, where /boot is located.

Example. 

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

Important

It is recommended to either bind an interface to a MAC with the ifname argument, or to use the systemd-udevd predictable network interface names.

Predictable network interface device names based on:

  • firmware/bios-provided index numbers for on-board devices
  • firmware-provided pci-express hotplug slot index number
  • physical/geographical location of the hardware
  • the interface’s MAC address

See: http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames

Two character prefixes based on the type of interface:

en
ethernet
wl
wlan
ww
wwan

Type of names:

o<index>
on-board device index number
s<slot>[f<function>][d<dev_id>]
hotplug slot index number
x<MAC>
MAC address
[P<domain>]p<bus>s<slot>[f<function>][d<dev_id>]
PCI geographical location
[P<domain>]p<bus>s<slot>[f<function>][u<port>][..][c<config>][i<interface>]
USB port number chain

All multi-function PCI devices will carry the [f<function>] number in the device name, including the function 0 device.

When using PCI geography, The PCI domain is only prepended when it is not 0.

For USB devices the full chain of port numbers of hubs is composed. If the name gets longer than the maximum number of 15 characters, the name is not exported. The usual USB configuration == 1 and interface == 0 values are suppressed.

PCI ethernet card with firmware index "1"
  • eno1
PCI ethernet card in hotplug slot with firmware index number
  • ens1
PCI ethernet multi-function card with 2 ports
  • enp2s0f0
  • enp2s0f1
PCI wlan card
  • wlp3s0
USB built-in 3G modem
  • wwp0s29u1u4i6
USB Android phone
  • enp0s29u1u2
ip={dhcp|on|any|dhcp6|auto6}
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
ip=<interface>:{dhcp|on|any|dhcp6|auto6}[:[<mtu>][:<macaddr>]]

This parameter can be specified multiple times.

dhcp|on|any|dhcp6
get ip from dhcp server on a specific interface
auto6
do IPv6 autoconfiguration
<macaddr>
optionally set <macaddr> on the <interface>. This cannot be used in conjunction with the ifname argument for the same <interface>.
ip=<client-IP>:[<peer>]:<gateway-IP>:<netmask>:<client_hostname>:<interface>:{none|off|dhcp|on|any|dhcp6|auto6|ibft}:[:[<mtu>][:<macaddr>]]

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. <peer> is optional and is the address of the remote endpoint for pointopoint interfaces and it may be followed by a slash and a decimal number, encoding the network prefix length.

<macaddr>
optionally set <macaddr> on the <interface>. This cannot be used in conjunction with the ifname argument for the same <interface>.
ip=<client-IP>:[<peer>]:<gateway-IP>:<netmask>:<client_hostname>:<interface>:{none|off|dhcp|on|any|dhcp6|auto6|ibft}[:[<dns1>][:<dns2>]]
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. <peer> is optional and is the address of the remote endpoint for pointopoint interfaces and it may be followed by a slash and a decimal number, encoding the network prefix length.
ifname=<interface>:<MAC>

Assign network device name <interface> (ie "bootnet") to the NIC with MAC <MAC>.

Warning

Do not use the default kernel naming scheme for the interface name, as it can conflict with the kernel names. So, don’t use "eth[0-9]+" for the interface name. Better name it "bootnet" or "bluesocket".

rd.route=<net>/<netmask>:<gateway>[:<interface>]

Add a static route with route options, which are separated by a colon. IPv6 addresses have to be put in brackets.

Example. 

    rd.route=192.168.200.0/24:192.168.100.222:ens10
    rd.route=192.168.200.0/24:192.168.100.222
    rd.route=192.168.200.0/24::ens10
    rd.route=[2001:DB8:3::/8]:[2001:DB8:2::1]:ens10

bootdev=<interface>
specify network interface to use routing and netroot information from. Required if multiple ip= lines are used.
BOOTIF=<MAC>
specify network interface to use routing and netroot information from.
rd.bootif=0
Disable BOOTIF parsing, which is provided by PXE
nameserver=<IP> [nameserver=<IP> …]
specify nameserver(s) to use
rd.peerdns=0
Disable DNS setting of DHCP parameters.
biosdevname=0
boolean, turn off biosdevname network interface renaming
rd.neednet=1
boolean, bring up network even without netroot set
vlan=<vlanname>:<phydevice>
Setup vlan device named <vlanname> on <phydeivce>. We support the four styles of vlan names: VLAN_PLUS_VID (vlan0005), VLAN_PLUS_VID_NO_PAD (vlan5), DEV_PLUS_VID (eth0.0005), DEV_PLUS_VID_NO_PAD (eth0.5)
bond=<bondname>[:<bondslaves>:[:<options>]]
Setup bonding device <bondname> on top of <bondslaves>. <bondslaves> is a comma-separated list of physical (ethernet) interfaces. <options> is a comma-separated list on bonding options (modinfo bonding for details) in format compatible with initscripts. If <options> includes multi-valued arp_ip_target option, then its values should be separated by semicolon. Bond without parameters assumes bond=bond0:eth0,eth1:mode=balance-rr
team=<teammaster>:<teamslaves>
Setup team device <teammaster> on top of <teamslaves>. <teamslaves> is a comma-separated list of physical (ethernet) interfaces.
bridge=<bridgename>:<ethnames>
Setup bridge <bridgename> with <ethnames>. <ethnames> is a comma-separated list of physical (ethernet) interfaces. Bridge without parameters assumes bridge=br0:eth0

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.

Example. 

    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.
rd.net.dhcp.retry=<cnt>
If this option is set, dracut will try to connect via dhcp <cnt> times before failing. Default is 1.
rd.net.timeout.dhcp=<arg>
If this option is set, dhclient is called with "-timeout <arg>".
rd.net.timeout.iflink=<seconds>
Wait <seconds> until link shows up. Default is 60 seconds.
rd.net.timeout.ifup=<seconds>
Wait <seconds> until link has state "UP". Default is 20 seconds.
rd.net.timeout.route=<seconds>
Wait <seconds> until route shows up. Default is 20 seconds.
rd.net.timeout.ipv6dad=<seconds>
Wait <seconds> until IPv6 DAD is finished. Default is 50 seconds.
rd.net.timeout.ipv6auto=<seconds>
Wait <seconds> until IPv6 automatic addresses are assigned. Default is 40 seconds.
rd.net.timeout.carrier=<seconds>
Wait <seconds> until carrier is recognized. Default is 5 seconds.

CIFS

root=cifs://[<username>[:<password>]@]<server-ip>:<root-dir>

mount cifs 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]. If a username or password are not specified as part of the root, then they must be passed on the command line through cifsuser/cifspass.

Warning

Passwords specified on the kernel command line are visible for all users via the file /proc/cmdline and via dmesg or can be sniffed on the network, when using DHCP with DHCP root-path.

cifsuser=<username>
Set the cifs username, if not specified as part of the root.
cifspass=<password>

Set the cifs password, if not specified as part of the root.

Warning

Passwords specified on the kernel command line are visible for all users via the file /proc/cmdline and via dmesg or can be sniffed on the network, when using DHCP with DHCP root-path.

iSCSI

root=iscsi:[<username>:<password>[:<reverse>:<password>]@][<servername>]:[<protocol>]:[<port>][:[<iscsi_iface_name>]:[<netdev_name>]]:[<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 rfc4173.

Warning

Passwords specified on the kernel command line are visible for all users via the file /proc/cmdline and via dmesg or can be sniffed on the network, when using DHCP with DHCP root-path.

Example. 

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

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

Example. 

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

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

multiple netroot options allow setting up multiple iscsi disks:

Example. 

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:

Example. 

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

Warning

Passwords specified on the kernel command line are visible for all users via the file /proc/cmdline and via dmesg or can be sniffed on the network, when using DHCP with DHCP root-path. You may want to use rd.iscsi.firmware.

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)

Warning

Passwords specified on the kernel command line are visible for all users via the file /proc/cmdline and via dmesg or can be sniffed on the network, when using DHCP with DHCP root-path. You may want to use rd.iscsi.firmware.

root=??? netroot=iscsi rd.iscsi.firmware=1
will read the iscsi parameter from the BIOS firmware
rd.iscsi.param=<param>

<param> will be passed as "--param <param>" to iscsistart. This parameter can be specified multiple times.

Example. 

"netroot=iscsi rd.iscsi.firmware=1 rd.iscsi.param=node.session.timeo.replacement_timeout=30"

will result in

iscsistart -b --param node.session.timeo.replacement_timeout=30

rd.iscsi.ibft rd.iscsi.ibft=1: Turn on iBFT autoconfiguration for the interfaces

rd.iscsi.waitnet=0: Turn off waiting for all interfaces to be up before trying to login to the iSCSI targets.

rd.iscsi.testroute=0: Turn off checking, if the route to the iSCSI target IP is possible before trying to login.

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=??? netroot=nbd:<server>:<port>[:<fstype>[:<mountopts>[:<nbdopts>]]]
mount nbd share from <server>
root=dhcp with dhcp root-path=nbd:<server>:<port>[:<fstype>[:<mountopts>[:<nbdopts>]]]
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=….
same syntax as the kernel module parameter (s390 only)

ZFCP

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

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

Example. 

rd.zfcp=0.0.4000,0x5005076300C213e9,0x5022000000000000

rd.zfcp.conf=0
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.

Example. 

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,protocol=bar

Booting live images

Dracut offers multiple options for live booted images:

SquashFS with read-only filesystem image

The system will boot with a read only filesystem from the SquashFS and apply a writable device-mapper snapshot over the read only filesystem. Using this method ensures a relatively fast boot and lower RAM usage. Users must be careful to avoid writing too many blocks to the snapshot volume. Once the blocks of the snapshot overlay are exhausted, the root filesystem becomes unusable and requires a reboot. A persistent overlay is marked Invalid, and requires a difficult recovery. Non-persistent overlays default to 512 MiB in RAM, but the size can be adjusted with the rd.live.overlay.size= kernel command line option.

The filesystem structure is expected to be:

squashfs.img          |  Squashfs from LiveCD .iso downloaded via network
   !(mount)
   /LiveOS
       |- ext3fs.img  |  Filesystem image to mount read-only
            !(mount)
            /bin      |  Live filesystem
            /boot     |
            /dev      |
            ...       |

Dracut uses this method of live booting by default. No additional command line options are required other than root=live:<URL> to specify the location of your squashed filesystem.

  • The compressed SquashFS image can be copied during boot to RAM at /run/initramfs/squashed.img by using the rd.live.ram=1 option.
  • A device with a persistent overlay can be booted read only by using the rd.live.overlay.readonly option on the kernel command line. This will cause a temporary, writable overlay to be stacked over a read-only snapshot of the root filesystem.
Uncompressed live filesystem image

When the live system was installed with the --skipcompress option of the livecd-iso-to-disk installation script for Live USB devices, the root filesystem image, ext3fs.img, is expanded on installation and no SquashFS is involved during boot.

  • If rd.live.ram=1 is used in this situation, the full, uncompressed root filesystem is copied during boot to /run/initramfs/rootfs.img in the /run tmpfs.
  • If rd.live.overlay=none is provided as a kernel command line option, a writable, linear device-mapper target is created on boot with no overlay.
writable filesystem image

The system will retrieve a compressed filesystem image, extract it to /run/initramfs/fsimg/rootfs.img, connect it to a loop device, create a writable, linear device-mapper target at /dev/mapper/live-rw, and mount that as a writable volume at /. More RAM is required during boot but the live filesystem is easier to manage if it becomes full. Users can make a filesystem image of any size and that size will be maintained when the system boots. There is no persistence of root filesystem changes between boots with this option.

The filesystem structure is expected to be:

rootfs.tgz            |  Compressed tarball containing fileystem image
   !(unpack)
   /rootfs.img        |  Filesystem image at /run/initramfs/fsimg/
      !(mount)
      /bin            |  Live filesystem
      /boot           |
      /dev            |
      ...             |

To use this boot option, ensure that rd.writable.fsimg=1 is in your kernel command line and add the root=live:<URL> to specify the location of your compressed filesystem image tarball or SquashFS image.

rd.writable.fsimg=1

Enables writable filesystem support. The system will boot with a fully writable (but non-persistent) filesystem without snapshots (see notes above about available live boot options). You can use the rootflags option to set mount options for the live filesystem as well (see documentation about rootflags in the Standard section above). This implies that the whole image is copied to RAM before the boot continues.

Note

There must be enough free RAM available to hold the complete image.

This method is very suitable for diskless boots.

root=live:<url>

Boots a live image retrieved from <url>. Valid handlers: http, https, ftp, torrent, tftp.

Example. 

root=live:http://example.com/liveboot.img
root=live:ftp://ftp.example.com/liveboot.img
root=live:torrent://example.com/liveboot.img.torrent

rd.live.debug=1
Enables debug output from the live boot process.
rd.live.dir=<path>
Specifies the directory within the squashfs where the ext3fs.img or rootfs.img can be found. By default, this is LiveOS.
rd.live.squashimg=<filename of SquashFS image>
Specifies the filename for a SquashFS image of the root filesystem. By default, this is squashfs.img.
rd.live.ram=1
Copy the complete image to RAM and use this for booting. This is useful when the image resides on, i.e., a DVD which needs to be ejected later on.
rd.live.overlay=<devspec>:(<pathspec>|auto)|none

Allow the usage of a permanent overlay.

  • <devspec> specifies the path to a device with a mountable filesystem.
  • <pathspec> is the path to a file within that filesystem, which shall be used to persist the changes made to the device specified by the root=live:<url> option.
  • none specifies no overlay when an uncompressed live root filesystem is available.

    Example. 

    rd.live.overlay=/dev/sdb1:persistent-overlay.img

rd.live.overlay.size=<size_MiB>
Specifies a non-persistent overlay size in MiB. The default is 512.
rd.live.overlay.readonly=1
Specifies a non-persistent, writable snapshot overlay to be stacked over a read-only snapshot of the root filesystem, /dev/mapper/live-ro.
rd.live.overlay.reset=1
Specifies that a persistent overlay should be reset on boot. All root filesystem changes are vacated by this action.
rd.live.overlay.thin=1
Enables the usage of thin snapshots instead of classic dm snapshots. The advantage of thin snapshots is that they support discards, and will free blocks that are not claimed by the filesystem. In this use case, this means that memory is given back to the kernel when the filesystem does not claim it anymore.

Plymouth Boot Splash

plymouth.enable=0
disable the plymouth bootsplash completely.
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.

Example. 

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

masterkeytype=<kernel master key type>

Set the type of the kernel master key.

Example. 

masterkeytype=trusted

evmkey=<EVM key path name>

Set the path name of the EVM key.

Example. 

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

ecryptfskey=<eCryptfs key path name>

Set the path name of the eCryptfs key.

Example. 

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
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_NO_MULTIPATH: rd.multipath=0

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. Deprecated, better use /etc/cmdline.d/*.conf.
/etc/cmdline.d/*.conf
Can contain additional command line options.

AUTHOR

Harald Hoyer

SEE ALSO

dracut(8) dracut.conf(5)

Chapter 9. LSINITRD(1)

NAME

lsinitrd - tool to show the contents of an initramfs image

SYNOPSIS

lsinitrd [OPTION…] [<image> [<filename> [<filename> […] ]]]

lsinitrd [OPTION…] -k <kernel-version>

DESCRIPTION

lsinitrd shows the contents of an initramfs image. if <image> is omitted, then lsinitrd uses the default image /boot/<machine-id>/<kernel-version>/initrd or /boot/initramfs-<kernel-version>.img.

OPTIONS

-h, --help
print a help message and exit.
-s, --size
sort the contents of the initramfs by size.
-f, --file <filename>
print the contents of <filename>.
-k, --kver <kernel version>
inspect the initramfs of <kernel version>.

AVAILABILITY

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

AUTHORS

Harald Hoyer

Amerigo Wang

Nikoli

SEE ALSO

dracut(8)

Chapter 10. MKINITRD(8)

NAME

mkinitrd - is a compat wrapper, which calls dracut to generate an initramfs

SYNOPSIS

mkinitrd [OPTION…] [<initrd-image>] <kernel-version>

DESCRIPTION

mkinitrd creates an initramfs image <initrd-image> for the kernel with version <kernel-version> by calling "dracut".

Important

If a more fine grained control over the resulting image is needed, "dracut" should be called directly.

OPTIONS

--version
print info about the version
-v, --verbose
increase verbosity level
-f, --force
overwrite existing initramfs file.
*--image-version
append the kernel version to the target image <initrd-image>-<kernel-version>.
--with=<module>
add the kernel module <module> to the initramfs.
--preload=<module>
preload the kernel module <module> in the initramfs before any other kernel modules are loaded. This can be used to ensure a certain device naming, which should in theory be avoided and the use of symbolic links in /dev is encouraged.
--nocompress
do not compress the resulting image.
--help
print a help message and exit.

AVAILABILITY

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

AUTHORS

Harald Hoyer

SEE ALSO

dracut(8)

Chapter 11. Developer Manual

Chapter 12. DRACUT.MODULES(7)

NAME

dracut.modules - dracut modules

DESCRIPTION

dracut uses a modular system to build and extend the initramfs image. All modules are located in /usr/lib/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 itself. 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

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.

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

In the main loop of dracut loops 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 (initqueue/settled) gets executed every time udev has settled.

Initqueue timeout

This hooks (initqueue/timeout) gets executed, when the main loop counter becomes half of the rd.retry counter.

Initqueue finished

This hook (initqueue/finished) is called after udev has settled and if all scripts herein return 0 the main loop will be ended. Abritary scripts can be added here, to loop in the initqueue until something happens, which a dracut module wants to wait for.

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 called before cleanup hook, This is a good place for actions other than cleanups which need to be called before pivot.

Hook: cleanup

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 (or systemd) 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

FIXME

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

module-setup.sh: 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.

module-setup.sh: depends()

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

module-setup.sh: cmdline()

This function should print the kernel command line options needed to boot the current machine setup. It should start with a space and should not print a newline.

module-setup.sh: install()

The install() function is called to install everything non-kernel related. To install binaries, scripts, and other files, you can use the functions mentioned in [creation].

To address a file in the current module directory, use the variable "$moddir".

module-setup.sh: installkernel()

In installkernel() all kernel related files should be installed. You can use all of the functions mentioned in [creation] to install files.

Creation Functions

inst_multiple [-o] <file> [ <file> …]

installs multiple binaries and files. If executables are specified without a path, dracut will search the path PATH=/usr/sbin:/sbin:/usr/bin:/bin for the binary. If the option "-o" is given as the first parameter, a missing file does not lead to an error.

inst <src> [<dst>]

installs one file <src> either to the same place in the initramfs or to an optional <dst>.

inst_hook <hookdir> <prio> <src>

installs an executable/script <src> in the dracut hook <hookdir> with priority <prio>.

inst_rules <udevrule> [ <udevrule> …]

installs one ore more udev rules. Non-existant udev rules are reported, but do not let dracut fail.

instmods <kernelmodule> [ <kernelmodule> … ]

instmods should be used only in the installkernel() function.

instmods installs one or more kernel modules in the initramfs. <kernelmodule> can also be a whole subsystem, if prefixed with a "=", like "=drivers/net/team".

instmods will not install the kernel module, if $hostonly is set and the kernel module is not currently needed by any /sys//uevent MODALIAS. To install a kernel module regardless of the hostonly mode use the form:

hostonly='' instmods <kernelmodule>

Initramfs Functions

FIXME

Network Modules

FIXME

AUTHOR

Harald Hoyer

SEE ALSO

dracut(8)

Chapter 13. DRACUT.BOOTUP(7)

NAME

dracut.bootup - boot ordering in the initramfs

DESCRIPTION

This flow chart illustrates the ordering of the services, if systemd is used in the dracut initramfs.

                                    systemd-journal.socket
                                               |
                                               v
                                    dracut-cmdline.service
                                               |
                                               v
                                    dracut-pre-udev.service
                                               |
                                               v
                                     systemd-udevd.service
                                               |
                                               v
local-fs-pre.target                dracut-pre-trigger.service
         |                                     |
         v                                     v
 (various mounts)  (various swap  systemd-udev-trigger.service
         |           devices...)               |             (various low-level   (various low-level
         |               |                     |             services: seed,       API VFS mounts:
         v               v                     v             tmpfiles, random     mqueue, configfs,
  local-fs.target   swap.target     dracut-initqueue.service    sysctl, ...)        debugfs, ...)
         |               |                     |                    |                    |
         \_______________|____________________ | ___________________|____________________/
                                              \|/
                                               v
                                        sysinit.target
                                               |
                             _________________/|\___________________
                            /                  |                    \
                            |                  |                    |
                            v                  |                    v
                        (various               |              rescue.service
                       sockets...)             |                    |
                            |                  |                    v
                            v                  |              rescue.target
                     sockets.target            |
                            |                  |
                            \_________________ |                                 emergency.service
                                              \|                                         |
                                               v                                         v
                                         basic.target                             emergency.target
                                               |
                        ______________________/|
                       /                       |
                       |                       v
                       |            dracut-pre-mount.service
                       |                       |
                       |                       v
                       |                  sysroot.mount
                       |                       |
                       |                       v
                       |             initrd-root-fs.target
           (custom initrd services)            |
                       |                       v
                       |             dracut-mount.service
                       |                       |
                       |                       v
                       |            initrd-parse-etc.service
                       |                       |
                       |                       v
                       |            (sysroot-usr.mount and
                       |             various mounts marked
                       |               with fstab option
                       |                x-initrd.mount)
                       |                       |
                       |                       v
                       |                initrd-fs.target
                       \______________________ |
                                              \|
                                               v
                                          initrd.target
                                               |
                                               v
                                    dracut-pre-pivot.service
                                               |
                                               v
                                     initrd-cleanup.service
                                          isolates to
                                    initrd-switch-root.target
                                               |
                                               v
                        ______________________/|
                       /                       |
                       |        initrd-udevadm-cleanup-db.service
                       |                       |
           (custom initrd services)            |
                       |                       |
                       \______________________ |
                                              \|
                                               v
                                   initrd-switch-root.target
                                               |
                                               v
                                   initrd-switch-root.service
                                               |
                                               v
                                          switch-root

AUTHOR

Harald Hoyer

SEE ALSO

dracut(8) bootup(7)

Appendix A. License

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.