dracut - low-level tool for generating an initramfs image at Linux.org

Back to main site | Back to man page index

DRACUT(8) dracut DRACUT(8)

NAME
dracut - low-level tool for generating an initramfs 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.

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 safed 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
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 usually can be configured in /boot/grub2/grub.cfg (or /boot/efi/EFI/redhat/grub.cfg
for EFI systems), if grub2 is your bootloader and it also can be edited in the real boot process in the grub
menu.

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

For a full reference of all kernel command line parameters, see 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

root=LABEL=myrootpartitionlabel

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

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

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

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

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

A typical german kernel command would contain:

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

`-- conf.d
`-- testvar.conf

# dracut --include rd.live.overlay / initramfs-rd.live.overlay.img

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

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

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

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

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

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

# yum install dracut-network

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

How to setup your PXE/TFTP server can be found in the Red Hat Enterprise Linux Storage Administration
Guide[1].

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

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 /boot/efi/EFI/redhat/grub.cfg for EFI systems)) 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. In /boot/grub2/grub.cfg (or /boot/efi/EFI/redhat/grub.cfg for EFI systems), add the following boot
arguments to the 'linux16' line:

console=tty0 console=ttyS0,9600

2. 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.

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
(or /boot/efi/EFI/redhat/grub.cfg for EFI systems))

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

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.

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.break=pre-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.

-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.

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

# dracut --modules "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" ...

-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.

# 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" ...

--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

--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

--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

--hostonly-i18n: Install only needed keyboard and font files according to the host configuration (default).

--no-hostonly-i18n: Install all keyboard and font files available.

--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".

--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.

--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.

--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.

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.

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

dracut 05/25/2017 DRACUT(8)