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.
43 ===============================
44 On RHEL-7 the hostonly mode is the default mode. Generic "non-hostonly" images
45 are created, if the dracut-config-generic rpm is installed. The rescue kernel
46 entry in the bootloader menu is also a generic image.
47 ===============================
49 === Inspecting the Contents
50 To see the contents of the image created by dracut, you can use the lsinitrd
56 To display the contents of a file in the initramfs also use the lsinitrd tool:
58 # lsinitrd -f /etc/ld.so.conf
59 include ld.so.conf.d/*.conf
62 === Adding dracut Modules
63 Some dracut modules are turned off by default and have to be activated manually.
64 You can do this by adding the dracut modules to the configuration file
65 _/etc/dracut.conf_ or _/etc/dracut.conf.d/myconf.conf_. See *dracut.conf*(5).
66 You can also add dracut modules on the command line
67 by using the -a or --add option:
69 # dracut --add bootchart initramfs-bootchart.img
72 To see a list of available dracut modules, use the --list-modules option:
74 # dracut --list-modules
77 === Omitting dracut Modules
78 Sometimes you don't want a dracut module to be included for reasons of speed,
79 size or functionality. To do this, either specify the omit_dracutmodules
80 variable in the _dracut.conf_ or _/etc/dracut.conf.d/myconf.conf_ configuration
81 file (see *dracut.conf*(5)), or use the -o or --omit option
84 # dracut -o "multipath lvm" no-multipath-lvm.img
87 === Adding Kernel Modules
88 If you need a special kernel module in the initramfs, which is not
89 automatically picked up by dracut, you have the use the --add-drivers option
90 on the command line or the drivers vaiable in the _/etc/dracut.conf_
91 or _/etc/dracut.conf.d/myconf.conf_ configuration file (see *dracut.conf*(5)):
93 # dracut --add-drivers mymod initramfs-with-mymod.img
97 An initramfs generated without the "hostonly" mode, does not contain any system
98 configuration files (except for some special exceptions), so the configuration
99 has to be done on the kernel command line. With this flexibility, you can easily
100 boot from a changed root partition, without the need to recompile the initramfs
101 image. So, you could completly change your root partition (move it inside a md
102 raid with encryption and LVM on top), as long as you specify the correct
103 filesystem LABEL or UUID on the kernel command line for your root device, dracut
104 will find it and boot from it.
106 The kernel command line usually can be configured in _/boot/grub2/grub.cfg_
107 (or _/boot/efi/EFI/redhat/grub.cfg_ for EFI systems), if
108 grub2 is your bootloader and it also can be edited in the real boot process in
111 The kernel command line can also be provided by the dhcp server with the
112 root-path option. See <<NetworkBoot>>.
114 For a full reference of all kernel command line parameters,
115 see *dracut.cmdline*(5).
117 To get a quick start for the suitable kernel command line on your system,
118 use the __--print-cmdline__ option:
120 # dracut --print-cmdline
121 root=UUID=8b8b6f91-95c7-4da2-831b-171e12179081 rootflags=rw,relatime,discard,data=ordered rootfstype=ext4
124 ==== Specifying the root Device
125 This is the only option dracut really needs to boot from your root partition.
126 Because your root partition can live in various environments, there are a lot of
127 formats for the root= option. The most basic one is root=_++<path to device
133 Because device node names can change, dependent on the drive ordering, you are
134 encouraged to use the filesystem identifier (UUID) or filesystem label (LABEL)
135 to specify your root partition:
137 root=UUID=19e9dda3-5a38-484d-a9b0-fa6b067d0331
143 root=LABEL=myrootpartitionlabel
146 To see all UUIDs or LABELs on your system, do:
148 # ls -l /dev/disk/by-uuid
154 # ls -l /dev/disk/by-label
157 If your root partition is on the network see <<NetworkBoot>>.
159 ==== Keyboard Settings
160 If you have to input passwords for encrypted disk volumes, you might want to set
161 the keyboard layout and specify a display font.
163 A typical german kernel command would contain:
165 rd.vconsole.font=latarcyrheb-sun16 rd.vconsole.keymap=de-latin1-nodeadkeys rd.locale.LANG=de_DE.UTF-8
168 Setting these options can override the setting stored on your system, if you use
169 a modern init system, like systemd.
171 ==== Blacklisting Kernel Modules
172 Sometimes it is required to prevent the automatic kernel module loading of a
173 specific kernel module. To do this, just add rd.blacklist=_++<kernel module
174 name>++_, with _++<kernel module name>++_ not containing the _.ko_
175 suffix, to the kernel command line. For example:
177 rd.driver.blacklist=mptsas rd.driver.blacklist=nouveau
180 The option can be specified multiple times on the kernel command line.
182 ==== Speeding up the Boot Process
183 If you want to speed up the boot process, you can specify as much information
184 for dracut on the kernel command as possible. For example, you can tell dracut,
185 that you root partition is not on a LVM volume or not on a raid partition, or
186 that it lives inside a specific crypto LUKS encrypted volume. By default, dracut
187 searches everywhere. A typical dracut kernel command line for a plain primary or
188 logical partition would contain:
190 rd.luks=0 rd.lvm=0 rd.md=0 rd.dm=0
193 This turns off every automatic assembly of LVM, MD raids, DM raids and
196 Of course, you could also omit the dracut modules in the initramfs creation
197 process, but then you would lose the posibility to turn it on on demand.
201 === Injecting custom Files
202 To add your own files to the initramfs image, you have several possibilities.
204 The --include option let you specify a source path and a target path.
207 # dracut --include cmdline-preset /etc/cmdline.d/mycmdline.conf initramfs-cmdline-pre.img
209 will create an initramfs image, where the file cmdline-preset will be copied
210 inside the initramfs to _/etc/cmdline.d/mycmdline.conf_. --include can only
215 # mkdir -p rd.live.overlay/etc/cmdline.d
216 # mkdir -p rd.live.overlay/etc/conf.d
217 # echo "ip=dhcp" >> rd.live.overlay/etc/cmdline.d/mycmdline.conf
218 # echo export FOO=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
219 # echo export BAR=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
220 # tree rd.live.overlay/
228 # dracut --include rd.live.overlay / initramfs-rd.live.overlay.img
231 This will put the contents of the rd.live.overlay directory into the root of the
234 The --install option let you specify several files, which will get installed in
235 the initramfs image at the same location, as they are present on initramfs
240 # dracut --install 'strace fsck.ext3 ssh' initramfs-dbg.img
243 This will create an initramfs with the strace, fsck.ext3 and ssh executables,
244 together with the libraries needed to start those. The --install option can be
245 specified multiple times.
251 If your root partition is on a network drive, you have to have the network
252 dracut modules installed to create a network aware initramfs image.
254 On a Red Hat Enterprise Linux or Fedora system, this means, you have to install
255 the _dracut-network_ rpm package:
259 # yum install dracut-network
262 The resulting initramfs image can be served by a boot manager residing on your
263 local hard drive or it can be served by a PXE/TFTP server.
265 How to setup your PXE/TFTP server can be found in the
266 http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/[Red
267 Hat Enterprise Linux Storage Administration Guide].
269 If you specify ip=dhcp on the kernel command line, then dracut asks a dhcp
270 server about the ip adress for the machine. The dhcp server can also serve an
271 additional root-path, which will set the root device for dracut. With this
272 mechanism, you have static configuration on your client machine and a
273 centralized boot configuration on your TFTP/DHCP server. If you can't pass a
274 kernel command line, then you can inject _/etc/cmdline.d/mycmdline.conf_, with a
275 method described in <<Injecting>>.
277 ==== Reducing the Image Size
279 To reduce the size of the initramfs, you should create it with by ommitting all
280 dracut modules, which you know, you don't need to boot the machine.
282 You can also specify the exact dracut and kernel modules to produce a very tiny
285 For example for a NFS image, you would do:
289 # dracut -m "nfs network base" initramfs-nfs-only.img
292 Then you would boot from this image with your target machine and reduce the size
293 once more by creating it on the target machine with the --host-only option:
297 # dracut -m "nfs network base" --host-only initramfs-nfs-host-only.img
300 This will reduce the size of the initramfs image significantly.
305 If the boot process does not succeed, you have several options to debug the
306 situation. Some of the basic operations are covered here. For more information
307 you should also visit:
308 http://fedoraproject.org/wiki/How_to_debug_Dracut_problems
311 [[identifying-your-problem-area]]
312 === Identifying your problem area
313 . Remove ''rhgb'' and ''quiet'' from the kernel command line
314 . Add ''rd.shell'' to the kernel command line. This will present a shell should
315 dracut be unable to locate your root device
316 . Add ''rd.shell rd.debug log_buf_len=1M'' to the kernel command line so that
317 dracut shell commands are printed as they are executed
318 . The file /run/initramfs/rdsosreport.txt is generated,
319 which contains all the logs and the output of all significant tools, which are
322 If you want to save that output, simply mount /boot by hand or insert an USB
323 stick and mount that. Then you can store the output for later inspection.
325 [[information-to-include-in-your-report]]
326 === Information to include in your report
330 In all cases, the following should be mentioned and attached to your bug report:
332 * The exact kernel command-line used. Typically from the bootloader
333 configuration file (e.g. _/boot/grub2/grub.cfg_ (or _/boot/efi/EFI/redhat/grub.cfg_ for EFI systems))
334 or from _/proc/cmdline_.
335 * A copy of your disk partition information from _/etc/fstab_, which might be
336 obtained booting an old working initramfs or a rescue medium.
337 * Turn on dracut debugging (see _the 'debugging dracut' section_), and attach
338 the file /run/initramfs/rdsosreport.txt.
339 * If you use a dracut configuration file, please include _/etc/dracut.conf_ and
340 all files in _/etc/dracut.conf.d/*.conf_
342 [[network-root-device-related-problems]]
343 ==== Network root device related problems
344 This section details information to include when experiencing problems on a
345 system whose root device is located on a network attached volume (e.g. iSCSI,
346 NFS or NBD). As well as the information from <<all-bug-reports>>, include the
347 following information:
350 * Please include the output of
353 # /sbin/ifup <interfacename>
361 [[configure-a-serial-console]]
362 ==== Configure a serial console
364 Successfully debugging dracut will require some form of console
365 logging during the system boot. This section documents configuring a
366 serial console connection to record boot messages.
368 . In _/boot/grub2/grub.cfg_ (or _/boot/efi/EFI/redhat/grub.cfg_ for EFI systems),
369 add the following boot arguments to the ''linux16''
373 console=tty0 console=ttyS0,9600
376 . More detailed information on how to configure the kernel for console output
378 http://www.faqs.org/docs/Linux-HOWTO/Remote-Serial-Console-HOWTO.html#CONFIGURE-KERNEL.
380 [[using-the-dracut-shell]]
381 ==== Using the dracut shell
383 dracut offers a shell for interactive debugging in the event dracut fails to
384 locate your root filesystem. To enable the shell:
386 . Add the boot parameter ''rd.shell'' to your bootloader configuration file
387 (e.g. _/boot/grub2/grub.cfg_ (or _/boot/efi/EFI/redhat/grub.cfg_ for EFI systems))
388 . Remove the boot arguments ''rhgb'' and ''quiet''
390 A sample _grub.cfg_ bootloader configuration file snippet is listed below.
393 menuentry 'Red Hat Enterprise Linux Server (3.10.0-308.el7.x86_64) 7.0 (Maipo)' […] {
395 linux16 /vmlinuz-3.10.0-308.el7.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 rd.shell
396 initrd16 /initramfs-3.10.0-308.el7.x86_64.img
401 . If system boot fails, you will be dropped into a shell as seen in the example
406 Dropping to debug shell.
411 . Use this shell prompt to gather the information requested above
412 (see <<all-bug-reports>>).
414 [[accessing-the-root-volume-from-the-dracut-shell]]
415 ==== Accessing the root volume from the dracut shell
416 From the dracut debug shell, you can manually perform the task of locating and
417 preparing your root volume for boot. The required steps will depend on how your
418 root volume is configured. Common scenarios include:
420 * A block device (e.g. _/dev/sda7_)
421 * A LVM logical volume (e.g. _/dev/VolGroup00/LogVol00_)
422 * An encrypted device
423 (e.g. _/dev/mapper/luks-4d5972ea-901c-4584-bd75-1da802417d83_)
424 * A network attached device
425 (e.g. _netroot=iscsi:@192.168.0.4::3260::iqn.2009-02.org.example:for.all_)
427 The exact method for locating and preparing will vary. However, to continue with
428 a successful boot, the objective is to locate your root volume and create a
429 symlink _/dev/root_ which points to the file system. For example, the following
430 example demonstrates accessing and booting a root volume that is an encrypted
433 . Inspect your partitions using parted
436 # parted /dev/sda -s p
437 Model: ATA HTS541060G9AT00 (scsi)
438 Disk /dev/sda: 60.0GB
439 Sector size (logical/physical): 512B/512B
440 Partition Table: msdos
441 Number Start End Size Type File system Flags
442 1 32.3kB 10.8GB 107MB primary ext4 boot
443 2 10.8GB 55.6GB 44.7GB logical lvm
446 . You recall that your root volume was a LVM logical volume. Scan and activate
454 . You should see any logical volumes now using the command blkid:
458 /dev/sda1: UUID="3de247f3-5de4-4a44-afc5-1fe179750cf7" TYPE="ext4"
459 /dev/sda2: UUID="Ek4dQw-cOtq-5MJu-OGRF-xz5k-O2l8-wdDj0I" TYPE="LVM2_member"
460 /dev/mapper/linux-root: UUID="def0269e-424b-4752-acf3-1077bf96ad2c" TYPE="crypto_LUKS"
461 /dev/mapper/linux-home: UUID="c69127c1-f153-4ea2-b58e-4cbfa9257c5e" TYPE="ext3"
462 /dev/mapper/linux-swap: UUID="47b4d329-975c-4c08-b218-f9c9bf3635f1" TYPE="swap"
465 . From the output above, you recall that your root volume exists on an encrypted
466 block device. Following the guidance disk encryption guidance from the
467 Installation Guide, you unlock your encrypted root volume.
470 # UUID=$(cryptsetup luksUUID /dev/mapper/linux-root)
471 # cryptsetup luksOpen /dev/mapper/linux-root luks-$UUID
472 Enter passphrase for /dev/mapper/linux-root:
476 . Next, make a symbolic link to the unlocked root volume
479 # ln -s /dev/mapper/luks-$UUID /dev/root
482 . With the root volume available, you may continue booting the system by exiting
489 [[additional-dracut-boot-parameters]]
490 ==== Additional dracut boot parameters
491 For more debugging options, see *dracut.cmdline*(7).
494 [[debugging-dracut-on-shutdown]]
495 ==== Debugging dracut on shutdown
497 To debug the shutdown sequence on systemd systems, you can _rd.break_
498 on _pre-shutdown_ or _shutdown_.
500 To do this from an already booted system:
502 # mkdir -p /run/initramfs/etc/cmdline.d
503 # echo "rd.break=pre-shutdown" > /run/initramfs/etc/cmdline.d/debug.conf
504 # touch /run/initramfs/.need_shutdown
507 This will give you a dracut shell after the system pivot'ed back in the