MKINITRD(8)MKINITRD(8)NAMEmkinitrd - create or rebuilt an initrd (initial ramdisk) using
initramfs (simple cpio+gzip).
SYNOPSISmkinitrd [ -F ] [ -c ] [ -f filesystem ] [ -h hibernate_partition ] [
-k kernel_version ] [ -m module1:module2:module3... ] [ -o output_file
] [ -r root_device ] [ -s source_tree ] [ -u ] [ -w wait_time ] [ -C
device1:device2:device3... ] [ -K luks_keyfile ] [ -B ] [ -L ] [ -R ]
[ -V ]
DESCRIPTIONmkinitrd is used to build an initial ramdisk. An initial ramdisk is a
very small set of files that are loaded into RAM and "mounted" (as
initramfs doesn't actually use a filesystem) as the kernel boots
(before the main root filesystem is mounted). The usual reason to use
an initrd is because you need to load kernel modules before mounting
the root partition. Usually these modules are required to support the
filesystem used by the root partition (ext3, reiserfs, xfs), or perhaps
the controller that the hard drive is attached to (SCSI, RAID, etc).
Essentially, there are so many different options available in modern
Linux kernels that it isn't practical to try to ship many different
kernels to try to cover everyone's needs. It's a lot more flexible to
ship a generic kernel and a set of kernel modules for it.
OPTIONS-F Use the contents of /etc/mkinitrd.conf as options to mkinitrd
(optional). If this is used in conjunction with any other
options passed on the command line, the command-line options
will override the config file options.
See mkinitrd.conf(5) for details.
-c Clear the existing initrd tree (by default in /boot/initrd-
tree/) first. If this is not done, running mkinitrd will add
additional modules to the existing initrd.
-f filesystem
Specify the filesystem to use for the root partition. If this
isn't given, mount will usually figure it out. This option must
be used together with the -r option in order to be beneficial.
--help Display a help summary.
-h hibernate_partition
Specify the swap partition holding the hibernation image.
-k kernel version
Use kernel modules from the specified kernel version. mkinitrd
will look for them in /lib/modules/(kernel version).
-l keymap
Load an alternative keyboard mapping. All supported keyboard
mappings can be found in /usr/share/mkinitrd/keymaps.tar.gz
Leave the '.bmap' out when you supply this parameter. E.g. '-l
nl' will add support for dutch keyboard mapping to the initrd.
-m module list
This is a list of colon-delimited modules to build into the ini‐
trd. Any dependencies of requested modules will also be added
to the initrd. Additional options may be added to use when
loading the kernel modules (but in this case the entire list
must be wrapped with double quotes).
-o output image
The file to write the initrd to. (default: /boot/initrd.gz)
-r root partition
Specify the device to be used as the root partition. If this
isn't given, the kernel default will be used (which is usually
fine). This option must be used together with the -f option in
order to be beneficial.
-s source tree
The directory to use as the source for the initrd. (default:
/boot/initrd-tree/)
-u Include udev in the initrd.
-w The -w option specifies how long to wait in seconds before
assuming that all the drives are spun up and ready to go.
-C device list
A colon (:) delimited list of luks encrypted block devices to be
unlocked by the initrd using cryptsetup. All devices that must
be unlocked in order to access the root filesystem must be spec‐
ified. e.g.
-C /dev/sda2:/dev/sda3
Each unlocked device will be assigned an automatically generated
luks device name of the form luks<device> where '<device>' will
be the basename of the encrypted device. e.g.
/dev/mapper/lukssda2
As a convenience to users, where -r specifies one of the device
names listed on the -C option it will be automatically adjusted
to use the correct luks device name. i.e.
"-C /dev/sda2 -r /dev/sda2" and
"-C /dev/sda2 -r /dev/mapper/lukssda2"
are equivalent.
(Use with '-r' option).
-K luks_keyfile
When using cryptsetup to encrypt your partition, you can use a
keyfile instead of a passphrase to unlock the LUKS volume. The
LUKSKEY variable holds the filename of a keyfile, as well as the
label (or uuid) of the partition this file is on. This way, you
can unlock your computer automatically if you have a USB stick
with your LUKS key inserted at boot. A passphrase will still be
asked if the LUKS key can not be found.
For example, if your USB thumb drive has a FAT partition with
label "TRAVELSTICK" and the actual keyfile is called
"/keys/alien.luks", then you need to set:
-K LABEL=TRAVELSTICK:/keys/alien.luks
-B This option adds the btrfs utility to the initrd so that multi-
device filesystems will be picked up by a scan (/sbin/btrfs
device scan). This is needed if the root filesystem is a Btrfs
multi-device filesystem.
-L This option adds LVM support to the initrd, if the tools are
available on the system.
-R This option adds RAID support to the initrd, if a static mdadm
binary is available on the system.
-V Display version information and exit.
EXAMPLES
A simple example: Build an initrd for a reiserfs root partition:
mkinitrd-c -m reiserfs
Another example: Build an initrd image using Linux 2.6.33.1 kernel
modules for a system with an ext3 root partition on /dev/sdb3:
mkinitrd-c -k 2.6.33.1 -m ext3 -f ext3 -r /dev/sdb3
An example of a single encrypted partition setup:
As a user convenience, the value for the "-r" option may also be speci‐
fied as "/dev/sda2" in this example:
mkinitrd-c -k 2.6.33.1 \
-m ext4:ehci-hcd:uhci-hcd:usbhid \
-f ext4 -r /dev/mapper/lukssda2 \
-C /dev/sda2 \
-l uk
Finally, A more complex example:
This one is for a LVM Volume Group (rootvg) comprising of two LVM Phys‐
ical Volumes, each of which is on a LUKS encrypted partition that will
need to be unlocked before the root filesystem (/dev/rootvg/lvroot) can
be accessed.
mkinitrd-c -k 2.6.29.6 \
-m ext4:ehci-hcd:uhci-hcd:usbhid \
-f ext4 -r /dev/rootvg/lvroot \
-L -C /dev/sda2:/dev/sdb2 \
-l uk
If run without options, mkinitrd will rebuild an initrd image using the
contents of the $SOURCE_TREE directory, or, if that directory does not
exist it will be created and populated, and then mkinitrd will exit.
These options are handy for building an initrd mostly by hand. After
creating /boot/initrd-tree/, you can add modules and edit files by
hand, and then rerun mkinitrd to create the initrd.
Once the initrd is created, you'll need to tell your boot loader to
load it. If you boot with LILO, you will need to add an initrd line to
/etc/lilo.conf. Here's a section of lilo.conf that shows how to set
this up:
# Linux bootable partition config begins
image = /boot/vmlinuz-generic-2.6.33.1
initrd = /boot/initrd.gz
root = /dev/sda3
label = Linux26331
read-only
# Linux bootable partition config ends
Note that the line "root = /dev/sda3" is not needed if the root device
has been configured in the initrd image.
Once you've created the initrd and editing /etc/lilo.conf, you will
need to run 'lilo' to write out the changed boot block. The next time
you reboot the initrd should be loaded along with the kernel.
Have fun!
SEE ALSO
mkinitrd.conf (5)
AUTHOR
Patrick J. Volkerding <volkerdi@slackware.com>
Slackware Version 13.1 27 March 2010 MKINITRD(8)
