1 To create a initramfs image, the most simple command is:
6 This will generate a general purpose initramfs image, with all possible
7 functionality resulting of the combination of the installed dracut modules and
8 system tools. The image is /boot/initramfs-_++<kernel version>++_.img and
9 contains the kernel modules of the currently active kernel with version
10 _++<kernel version>++_.
12 If the initramfs image already exists, dracut will display an error message, and
13 to overwrite the existing image, you have to use the --force option.
18 If you want to specify another filename for the resulting image you would issue
24 To generate an image for a specific kernel version, the command would be:
26 # dracut foobar.img 2.6.40-1.rc5.f20
29 A shortcut to generate the image at the default location for a specific kernel
32 # dracut --kver 2.6.40-1.rc5.f20
35 If you want to create lighter, smaller initramfs images, you may want to specify
36 the --hostonly or -H option. Using this option, the resulting image will
37 contain only those dracut modules, kernel modules and filesystems, which are
38 needed to boot this specific machine. This has the drawback, that you can't put
39 the disk on another controller or machine, and that you can't switch to another
40 root filesystem, without recreating the initramfs image. The usage of the
41 --hostonly option is only for experts and you will have to keep the broken
42 pieces. At least keep a copy of a general purpose image (and corresponding
43 kernel) as a fallback to rescue your system.
45 === Inspecting the Contents
46 To see the contents of the image created by dracut, you can use the lsinitrd
52 To display the contents of a file in the initramfs also use the lsinitrd tool:
54 # lsinitrd -f /etc/ld.so.conf
55 include ld.so.conf.d/*.conf
58 === Adding dracut Modules
59 Some dracut modules are turned off by default and have to be activated manually.
60 You can do this by adding the dracut modules to the configuration file
61 _/etc/dracut.conf_ or _/etc/dracut.conf.d/myconf.conf_. See *dracut.conf*(5).
62 You can also add dracut modules on the command line
63 by using the -a or --add option:
65 # dracut --add bootchart initramfs-bootchart.img
68 To see a list of available dracut modules, use the --list-modules option:
70 # dracut --list-modules
73 === Omitting dracut Modules
74 Sometimes you don't want a dracut module to be included for reasons of speed,
75 size or functionality. To do this, either specify the omit_dracutmodules
76 variable in the _dracut.conf_ or _/etc/dracut.conf.d/myconf.conf_ configuration
77 file (see *dracut.conf*(5)), or use the -o or --omit option
80 # dracut -o "multipath lvm" no-multipath-lvm.img
83 === Adding Kernel Modules
84 If you need a special kernel module in the initramfs, which is not
85 automatically picked up by dracut, you have the use the --add-drivers option
86 on the command line or the drivers vaiable in the _/etc/dracut.conf_
87 or _/etc/dracut.conf.d/myconf.conf_ configuration file (see *dracut.conf*(5)):
89 # dracut --add-drivers mymod initramfs-with-mymod.img
93 An initramfs generated without the "hostonly" mode, does not contain any system
94 configuration files (except for some special exceptions), so the configuration
95 has to be done on the kernel command line. With this flexibility, you can easily
96 boot from a changed root partition, without the need to recompile the initramfs
97 image. So, you could completly change your root partition (move it inside a md
98 raid with encryption and LVM on top), as long as you specify the correct
99 filesystem LABEL or UUID on the kernel command line for your root device, dracut
100 will find it and boot from it.
102 The kernel command line usually can be configured in _/boot/grub/grub.conf_, if
103 grub is your bootloader and it also can be edited in the real boot process in
106 The kernel command line can also be provided by the dhcp server with the
107 root-path option. See <<NetworkBoot>>.
109 For a full reference of all kernel command line parameters,
110 see *dracut.cmdline*(5).
112 To get a quick start for the suitable kernel command line on your system,
113 use the __--print-cmdline__ option:
115 # dracut --print-cmdline
116 root=UUID=8b8b6f91-95c7-4da2-831b-171e12179081 rootflags=rw,relatime,discard,data=ordered rootfstype=ext4
119 ==== Specifying the root Device
120 This is the only option dracut really needs to boot from your root partition.
121 Because your root partition can live in various environments, there are a lot of
122 formats for the root= option. The most basic one is root=_++<path to device
128 Because device node names can change, dependent on the drive ordering, you are
129 encouraged to use the filesystem identifier (UUID) or filesystem label (LABEL)
130 to specify your root partition:
132 root=UUID=19e9dda3-5a38-484d-a9b0-fa6b067d0331
138 root=LABEL=myrootpartitionlabel
141 To see all UUIDs or LABELs on your system, do:
143 # ls -l /dev/disk/by-uuid
149 # ls -l /dev/disk/by-label
152 If your root partition is on the network see <<NetworkBoot>>.
154 ==== Keyboard Settings
155 If you have to input passwords for encrypted disk volumes, you might want to set
156 the keyboard layout and specify a display font.
158 A typical german kernel command would contain:
160 rd.vconsole.font=latarcyrheb-sun16 rd.vconsole.keymap=de-latin1-nodeadkeys rd.locale.LANG=de_DE.UTF-8
163 Setting these options can override the setting stored on your system, if you use
164 a modern init system, like systemd.
166 ==== Blacklisting Kernel Modules
167 Sometimes it is required to prevent the automatic kernel module loading of a
168 specific kernel module. To do this, just add rd.blacklist=_++<kernel module
169 name>++_, with _++<kernel module name>++_ not containing the _.ko_
170 suffix, to the kernel command line. For example:
172 rd.driver.blacklist=mptsas rd.driver.blacklist=nouveau
175 The option can be specified multiple times on the kernel command line.
177 ==== Speeding up the Boot Process
178 If you want to speed up the boot process, you can specify as much information
179 for dracut on the kernel command as possible. For example, you can tell dracut,
180 that you root partition is not on a LVM volume or not on a raid partition, or
181 that it lives inside a specific crypto LUKS encrypted volume. By default, dracut
182 searches everywhere. A typical dracut kernel command line for a plain primary or
183 logical partition would contain:
185 rd.luks=0 rd.lvm=0 rd.md=0 rd.dm=0
188 This turns off every automatic assembly of LVM, MD raids, DM raids and
191 Of course, you could also omit the dracut modules in the initramfs creation
192 process, but then you would lose the posibility to turn it on on demand.
196 === Injecting custom Files
197 To add your own files to the initramfs image, you have several possibilities.
199 The --include option let you specify a source path and a target path.
202 # dracut --include cmdline-preset /etc/cmdline.d/mycmdline.conf initramfs-cmdline-pre.img
204 will create an initramfs image, where the file cmdline-preset will be copied
205 inside the initramfs to _/etc/cmdline.d/mycmdline.conf_. --include can only
210 # mkdir -p rd.live.overlay/etc/cmdline.d
211 # mkdir -p rd.live.overlay/etc/conf.d
212 # echo "ip=auto" >> rd.live.overlay/etc/cmdline.d/mycmdline.conf
213 # echo export FOO=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
214 # echo export BAR=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
215 # tree rd.live.overlay/
223 # dracut --include rd.live.overlay / initramfs-rd.live.overlay.img
226 This will put the contents of the rd.live.overlay directory into the root of the
229 The --install option let you specify several files, which will get installed in
230 the initramfs image at the same location, as they are present on initramfs
235 # dracut --install 'strace fsck.ext3 ssh' initramfs-dbg.img
238 This will create an initramfs with the strace, fsck.ext3 and ssh executables,
239 together with the libraries needed to start those. The --install option can be
240 specified multiple times.
246 If your root partition is on a network drive, you have to have the network
247 dracut modules installed to create a network aware initramfs image.
249 On a Red Hat Enterprise Linux or Fedora system, this means, you have to install
250 the _dracut-network_ rpm package:
254 # yum install dracut-network
257 The resulting initramfs image can be served by a boot manager residing on your
258 local hard drive or it can be served by a PXE/TFTP server.
260 How to setup your PXE/TFTP server can be found in the
261 http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/[Red
262 Hat Enterprise Linux Storage Administration Guide].
264 If you specify ip=auto on the kernel command line, then dracut asks a dhcp
265 server about the ip adress for the machine. The dhcp server can also serve an
266 additional root-path, which will set the root device for dracut. With this
267 mechanism, you have static configuration on your client machine and a
268 centralized boot configuration on your TFTP/DHCP server. If you can't pass a
269 kernel command line, then you can inject _/etc/cmdline.d/mycmdline.conf_, with a
270 method described in <<Injecting>>.
272 ==== Reducing the Image Size
274 To reduce the size of the initramfs, you should create it with by ommitting all
275 dracut modules, which you know, you don't need to boot the machine.
277 You can also specify the exact dracut and kernel modules to produce a very tiny
280 For example for a NFS image, you would do:
284 # dracut -m "nfs network base" initramfs-nfs-only.img
287 Then you would boot from this image with your target machine and reduce the size
288 once more by creating it on the target machine with the --host-only option:
292 # dracut -m "nfs network base" --host-only initramfs-nfs-host-only.img
295 This will reduce the size of the initramfs image significantly.
300 If the boot process does not succeed, you have several options to debug the
301 situation. Some of the basic operations are covered here. For more information
302 you should also visit:
303 http://fedoraproject.org/wiki/How_to_debug_Dracut_problems
306 [[identifying-your-problem-area]]
307 === Identifying your problem area
308 . Remove ''rhgb'' and ''quiet'' from the kernel command line
309 . Add ''rd.shell'' to the kernel command line. This will present a shell should
310 dracut be unable to locate your root device
311 . Add ''rd.shell rd.debug log_buf_len=1M'' to the kernel command line so that
312 dracut shell commands are printed as they are executed
313 . The file /run/initramfs/rdsosreport.txt is generated,
314 which contains all the logs and the output of all significant tools, which are
317 If you want to save that output, simply mount /boot by hand or insert an USB
318 stick and mount that. Then you can store the output for later inspection.
320 [[information-to-include-in-your-report]]
321 === Information to include in your report
325 In all cases, the following should be mentioned and attached to your bug report:
327 * The exact kernel command-line used. Typically from the bootloader
328 configuration file (e.g. _/etc/grub.conf_) or from _/proc/cmdline_.
329 * A copy of your disk partition information from _/etc/fstab_, which might be
330 obtained booting an old working initramfs or a rescue medium.
331 * Turn on dracut debugging (see _the 'debugging dracut' section_), and attach
332 the file /run/initramfs/rdsosreport.txt.
333 * If you use a dracut configuration file, please include _/etc/dracut.conf_ and
334 all files in _/etc/dracut.conf.d/*.conf_
336 [[network-root-device-related-problems]]
337 ==== Network root device related problems
338 This section details information to include when experiencing problems on a
339 system whose root device is located on a network attached volume (e.g. iSCSI,
340 NFS or NBD). As well as the information from <<all-bug-reports>>, include the
341 following information:
344 * Please include the output of
347 # /sbin/ifup <interfacename>
355 [[configure-a-serial-console]]
356 ==== Configure a serial console
358 Successfully debugging dracut will require some form of console
359 logging during the system boot. This section documents configuring a
360 serial console connection to record boot messages.
362 . First, enable serial console output for both the kernel and the bootloader.
363 . Open the file _/etc/grub.conf_ for editing. Below the line ''timeout=5'', add
367 serial --unit=0 --speed=9600
368 terminal --timeout=5 serial console
371 . Also in _/etc/grub.conf_, add the following boot arguemnts to the ''kernel''
375 console=tty0 console=ttyS0,9600
378 . When finished, the _/etc/grub.conf_ file should look similar to the example
384 serial --unit=0 --speed=9600
385 terminal --timeout=5 serial console
386 title Fedora (2.6.29.5-191.fc11.x86_64)
388 kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 console=ttyS0,9600
389 initrd /dracut-2.6.29.5-191.fc11.x86_64.img
392 . More detailed information on how to configure the kernel for console output
394 http://www.faqs.org/docs/Linux-HOWTO/Remote-Serial-Console-HOWTO.html#CONFIGURE-KERNEL.
395 . Redirecting non-interactive output
398 NOTE: You can redirect all non-interactive output to _/dev/kmsg_ and the kernel
399 will put it out on the console when it reaches the kernel buffer by doing
402 # exec >/dev/kmsg 2>&1 </dev/console
406 [[using-the-dracut-shell]]
407 ==== Using the dracut shell
409 dracut offers a shell for interactive debugging in the event dracut fails to
410 locate your root filesystem. To enable the shell:
412 . Add the boot parameter ''rd.shell'' to your bootloader configuration file
413 (e.g. _/etc/grub.conf_)
414 . Remove the boot arguments ''rhgb'' and ''quiet''
416 A sample _/etc/grub.conf_ bootloader configuration file is listed below.
421 serial --unit=0 --speed=9600
422 terminal --timeout=5 serial console
423 title Fedora (2.6.29.5-191.fc11.x86_64)
425 kernel /vmlinuz-2.6.29.5-191.fc11.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 rd.shell
426 initrd /dracut-2.6.29.5-191.fc11.x86_64.img
429 . If system boot fails, you will be dropped into a shell as seen in the example
434 Dropping to debug shell.
439 . Use this shell prompt to gather the information requested above
440 (see <<all-bug-reports>>).
442 [[accessing-the-root-volume-from-the-dracut-shell]]
443 ==== Accessing the root volume from the dracut shell
444 From the dracut debug shell, you can manually perform the task of locating and
445 preparing your root volume for boot. The required steps will depend on how your
446 root volume is configured. Common scenarios include:
448 * A block device (e.g. _/dev/sda7_)
449 * A LVM logical volume (e.g. _/dev/VolGroup00/LogVol00_)
450 * An encrypted device
451 (e.g. _/dev/mapper/luks-4d5972ea-901c-4584-bd75-1da802417d83_)
452 * A network attached device
453 (e.g. _netroot=iscsi:@192.168.0.4::3260::iqn.2009-02.org.example:for.all_)
455 The exact method for locating and preparing will vary. However, to continue with
456 a successful boot, the objective is to locate your root volume and create a
457 symlink _/dev/root_ which points to the file system. For example, the following
458 example demonstrates accessing and booting a root volume that is an encrypted
461 . Inspect your partitions using parted
464 # parted /dev/sda -s p
465 Model: ATA HTS541060G9AT00 (scsi)
466 Disk /dev/sda: 60.0GB
467 Sector size (logical/physical): 512B/512B
468 Partition Table: msdos
469 Number Start End Size Type File system Flags
470 1 32.3kB 10.8GB 107MB primary ext4 boot
471 2 10.8GB 55.6GB 44.7GB logical lvm
474 . You recall that your root volume was a LVM logical volume. Scan and activate
482 . You should see any logical volumes now using the command blkid:
486 /dev/sda1: UUID="3de247f3-5de4-4a44-afc5-1fe179750cf7" TYPE="ext4"
487 /dev/sda2: UUID="Ek4dQw-cOtq-5MJu-OGRF-xz5k-O2l8-wdDj0I" TYPE="LVM2_member"
488 /dev/mapper/linux-root: UUID="def0269e-424b-4752-acf3-1077bf96ad2c" TYPE="crypto_LUKS"
489 /dev/mapper/linux-home: UUID="c69127c1-f153-4ea2-b58e-4cbfa9257c5e" TYPE="ext3"
490 /dev/mapper/linux-swap: UUID="47b4d329-975c-4c08-b218-f9c9bf3635f1" TYPE="swap"
493 . From the output above, you recall that your root volume exists on an encrypted
494 block device. Following the guidance disk encryption guidance from the
495 Installation Guide, you unlock your encrypted root volume.
498 # UUID=$(cryptsetup luksUUID /dev/mapper/linux-root)
499 # cryptsetup luksOpen /dev/mapper/linux-root luks-$UUID
500 Enter passphrase for /dev/mapper/linux-root:
504 . Next, make a symbolic link to the unlocked root volume
507 # ln -s /dev/mapper/luks-$UUID /dev/root
510 . With the root volume available, you may continue booting the system by exiting
517 [[additional-dracut-boot-parameters]]
518 ==== Additional dracut boot parameters
519 For more debugging options, see *dracut.cmdline*(7).
522 [[debugging-dracut-on-shutdown]]
523 ==== Debugging dracut on shutdown
525 To debug the shutdown sequence on systemd systems, you can _rd.break_
526 on _pre-shutdown_ or _shutdown_.
528 To do this from an already booted system:
530 # mkdir -p /run/initramfs/etc/cmdline.d
531 # echo "rd.break=pre-shutdown" > /run/initramfs/etc/cmdline.d/debug.conf
532 # touch /run/initramfs/.need_shutdown
535 This will give you a dracut shell after the system pivot'ed back in the