dracut

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

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

# dracut --force

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

# dracut foobar.img

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

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

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

# dracut '' 2.6.40-1.rc5.f20

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

Inspecting the Contents

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

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

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

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

Adding dracut Modules

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

# dracut --add bootchart initramfs-bootchart.img

To see a list of available dracut modules, issue the command:

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

Omitting dracut Modules

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

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

Adding Kernel Modules

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

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

dracut searches for kernel modules in

/lib/modules/<kernel version>/kernel/drivers
/lib/modules/<kernel version>/updates
/lib/modules/<kernel version>/extra
/lib/modules/<kernel version>/weak-updates

Boot parameters

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

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

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

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

Specifying the root Device

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

root=/dev/sda2

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

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

root=LABEL=myrootpartitionlabel

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

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

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

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

Keyboard Settings

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

A typical german kernel command would contain:

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

Force loading of Kernel Modules

dracut can force load a kernel module with the rdloaddriver=<drivername> kernel command line parameter, if the kernel module is included in the initramfs (see previous section). If you want the kernel module to be force loaded after all automatic loading modules have been loaded, use the rdrdinsmodpost=<drivername> kernel command line parameter.

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:

rdblacklist=mptsas rdblacklist=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_NO_LUKS rd_NO_LVM rd_NO_MD rd_NO_DM

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

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

Injecting custom Files

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

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

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

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

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

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

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

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

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

Network Boot

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

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

# yum install dracut-network

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

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

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

Reducing the Image Size

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

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

For example for a NFS image, you would do:

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

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

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

This will reduce the size of the initramfs image significantly.

Troubleshooting

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

Identifying your problem area

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

Information to include in your report

All bug reports

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

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

Logical Volume Management related problems

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

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

Software RAID related problems

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

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

Network root device related problems

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

Please include the output of

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

Debugging dracut

Configure a serial console

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

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

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

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

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

Redirecting non-interactive output

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

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

Using the dracut shell

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

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

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

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

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

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

No root device found 
       Dropping to debug shell.

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

       #

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

Accessing the root volume from the dracut shell

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

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

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

Inspect your partitions using parted

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

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

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

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

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

Additional dracut boot parameters

For more debugging options, see the section called “Debug” in the man page dracut(8).

Appendix A. Man Pages

Table of Contents

dracut

dracut — create initial ramdisk images for preloading modules

dracut.conf

dracut.conf — configuration file(s) for dracut

dracut.kernel

dracut — dracut kernel command line options

dracut

Name

dracut — create initial ramdisk images for preloading modules

Synopsis

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

Description

dracut creates an initial image used by the kernel for preloading the block device modules (such as IDE, SCSI or RAID) which are needed to access the root filesystem.

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

Options

-f , --force: overwrite existing initramfs file.
-m , --modules <list of dracut modules>: specify a space-separated list of dracut modules to call when building the initramfs. Modules are located in /usr/share/dracut/modules.d. This parameter can be specified multiple times.
-o , --omit <list of dracut modules>: omit a space-separated list of dracut modules. This parameter can be specified multiple times.
-a , --add <list of dracut modules>: add a space-separated list of dracut modules to the default set of modules. This parameter can be specified multiple times.
-d , --drivers <list of kernel modules>: specify a space-separated list of kernel modules to exclusively include in the initramfs. The kernel modules have to be specified without the ".ko" suffix. This parameter can be specified multiple times.
--add-drivers <list of kernel modules>: specify a space-separated list of kernel modules to add to the initramfs. The kernel modules have to be specified without the ".ko" suffix. This parameter can be specified multiple times.
--filesystems <list of filesystems>: specify a space-separated list of kernel filesystem modules to exclusively include in the generic initramfs. This parameter can be specified multiple times.
-k , --kmoddir <kernel directory>: specify the directory, where to look for kernel modules
--fwdir <dir>[:<dir>...]: specify additional directories, where to look for firmwares. This parameter can be specified multiple times.
--kernel-only: only install kernel drivers and firmware files
--no-kernel: do not install kernel drivers and firmware files
--mdadmconf: include local /etc/mdadm.conf
--nomdadmconf: do not include local /etc/mdadm.conf
--strip: strip binaries in the initramfs (default)
--nostrip: do not strip binaries in the initramfs
-h , --help: display help text and exit.
--debug: output debug information of the build process
-v , --verbose: verbose output during the build process
-c , --conf <dracut configuration file>: specify configuration file to use. Default: /etc/dracut.conf
--confdir <configuration directory>: specify configuration directory to use. Default: /etc/dracut.conf.d
-l , --local: activates the local mode. dracut will use modules from the current working directory instead of the system-wide installed modules in /usr/share/dracut/modules.d. This is useful when running dracut from a git checkout.
-H , --hostonly: Host-Only mode: Install only what is needed for booting the local host instead of a generic host.
Warning
If chrooted to another root other than the real root device, use "--fstab" and provide a valid /etc/fstab.
--fstab: Use /etc/fstab instead of /proc/self/mountinfo.
-i , --include <source directory> <target directory>: include the files in the source directory into the target directory in the final initramfs.
-I , --install <file list>: install the space separated list of files into the initramfs.

Files

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

Configuration in the Initramfs

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

Availability

The dracut command is part of the dracut package and is available from http://sourceforge.net/apps/trac/dracut/wiki

dracut.conf

Name

dracut.conf — configuration file(s) for dracut

Synopsis

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

Description

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

dracutmodules+=" <dracut modules> "

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

omit_dracutmodules+=" <dracut modules> "

Omit a space-separated list of dracut modules.

add_dracutmodules+=" <dracut modules> "

Add a space-separated list of dracut modules.

drivers+=" <kernel modules> "

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

add_drivers+=" <kernel modules> "

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

filesystems+=" <filesystem names> "

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

drivers_dir="<kernel modules directory>"

Specify the directory, where to look for kernel modules

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

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

do_strip="{yes|no}"

Strip binaries in the initramfs (default=yes)

hostonly="{yes|no}"

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

Warning

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

use_fstab="{yes|no}"

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

mdadmconf="{yes|no}"

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

lvmconf="{yes|no}"

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

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)

Files

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

dracut.kernel

Name

dracut.kernel — dracut kernel command line options

Description

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

Standard

init=<path to real init>

root=<path to blockdevice>

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

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

rootfstype=<filesystem type>

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

rootfstype=ext3

rootflags=<mount options>

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

Misc

rdblacklist=<drivername>[,<drivername>,...]: do not load kernel module <drivername> This parameter can be specified multiple times.
rdloaddriver=<drivername>[,<drivername>,...]: force loading kernel module <drivername> This parameter can be specified multiple times.
rdrdinsmodpost=<drivername>[,<drivername>,...]: force loading kernel module <drivername> after all automatic loading modules have been loaded. This parameter can be specified multiple times.

Debug

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

I18N

e.g.

LANG=en_US.UTF-8
SYSFONT=latarcyrheb-sun16
KEYTABLE=de-latin1-nodeadkeys

KEYBOARDTYPE= sun|pc: will be written to /etc/sysconfig/keyboard in the initramfs
KEYTABLE= <keytable filename>: will be written to /etc/sysconfig/keyboard in the initramfs
SYSFONT= <console font>: will be written to /etc/sysconfig/i18n in the initramfs
SYSFONTACM= <console font map>: will be written to /etc/sysconfig/i18n in the initramfs
UNIMAP= <unicode font map>: will be written to /etc/sysconfig/i18n in the initramfs
LANG= <locale>: will be written to /etc/sysconfig/i18n in the initramfs

LVM

rd_NO_LVM: disable LVM detection
rd_NO_LVM.vg=<volume group name>: only activate the volume groups with the given name rd_NO_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_NO_LVMCONF: remove any /etc/lvm/lvm.conf, which may exist in the initramfs

crypto LUKS

rd_NO_LUKS: 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_NO_CRYPTTAB: do not check, if LUKS partition is in /etc/crypttab

MD

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

DM RAID

rd_NO_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.

Network

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}

dhcp|on|any|dhcp6: get ip from dhcp server on a specific interface auto6: do IPv6 autoconfiguration This parameter can be specified multiple times.

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

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

ifname=<interface>:<MAC>

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

bootdev= <interface>

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

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

specify nameserver(s) to use

biosdevname= {0|1}

turn on/off biosdevname network interface renaming

NFS

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

iSCSI

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

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

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

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

e.g.:

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

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

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

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

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

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

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

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

root=??? iscsi_initiator=<initiator> iscsi_target_name=<target name> iscsi_target_ip=<target ip> iscsi_target_port=<target port> iscsi_target_group=<target group> iscsi_username=<username> iscsi_password=<password> iscsi_in_username=<in username> iscsi_in_password=<in password>

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

root= ??? netroot=iscsi iscsi_firmware

will read the iscsi parameter from the BIOS firmware

FCoE

netroot=fcoe:<interface|MAC>:{dcb|nodcb}: Try to connect to a FCoE SAN through the NIC specified by <interface> or <MAC>, for the second argument, currently only nodcb is supported. Note: letters in the MAC-address must be lowercase!

NBD

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

DASD

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

ZFCP

rd_ZFCP=<zfcp adaptor device bus ID>,<WWPN>,<FCPLUN>

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

rd_ZFCP=0.0.4000,0x5005076300C213e9,0x5022000000000000

rd_NO_ZFCPCONF

ignore zfcp.conf included in the initramfs

ZNET

rd_ZNET=<nettype>,<subchannels>,<options>

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

rd_ZNET=qeth,0.0.0600,0.0.0601,0.0.0602,layer2=1,portname=foo
    rd_ZNET=ctc,0.0.0600,0.0.0601,0.0.0602,protocol=bar

Plymouth Boot Splash

rd_NO_PLYMOUTH: disable plymouth. This will not work with encrypted partitions.

Configuration in the Initramfs

/conf/conf.d/: Any files found in /conf/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.

dracut

Harald Hoyer

Chapter 1. User Manual

Creating an initramfs Image

Inspecting the Contents

Adding dracut Modules

Omitting dracut Modules

Adding Kernel Modules

Boot parameters

Specifying the root Device

Keyboard Settings

Force loading of Kernel Modules

Blacklisting Kernel Modules

Speeding up the Boot Process

Injecting custom Files

Network Boot

Reducing the Image Size

Troubleshooting

Identifying your problem area

Information to include in your report

All bug reports

Logical Volume Management related problems

Software RAID related problems

Network root device related problems

Debugging dracut

Configure a serial console

Redirecting non-interactive output

Using the dracut shell

Accessing the root volume from the dracut shell

Additional dracut boot parameters

Appendix A. Man Pages

dracut

Name

Synopsis

Description

Options

Warning

Files

Configuration in the Initramfs

Availability

See Also

dracut.conf

Name

Synopsis

Description

Warning

Files

See Also

dracut.kernel

Name

Description

Standard

Misc

Debug

I18N

LVM

crypto LUKS

MD

DM RAID

Network

NFS

iSCSI

FCoE

NBD

DASD

ZFCP

ZNET

Plymouth Boot Splash

Configuration in the Initramfs

See Also