Merge pull request #172 from haraldh/RHEL-7

[thirdparty/dracut.git] / dracut.usage.asc

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 image.

[NOTE]
===============================
On RHEL-7 the hostonly mode is the default mode. Generic "non-hostonly" images
are created, if the dracut-config-generic rpm is installed. The rescue kernel
entry in the bootloader menu is also a generic image.
===============================

=== Inspecting the Contents
To see the contents of the image created by dracut, you can use the lsinitrd
tool.
----
# lsinitrd | less
----

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 <<NetworkBoot>>.

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 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
----

or

----
root=LABEL=myrootpartitionlabel
----

To see all UUIDs or LABELs on your system, do:
----
# ls -l /dev/disk/by-uuid
----

or

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

If your root partition is on the network see <<NetworkBoot>>.

==== 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]]
=== 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 _/etc/cmdline.d/mycmdline.conf_. --include can only
be specified once.


----
# mkdir -p rd.live.overlay/etc/cmdline.d
# mkdir -p rd.live.overlay/etc/conf.d
# echo "ip=dhcp" >> rd.live.overlay/etc/cmdline.d/mycmdline.conf
# echo export FOO=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
# echo export BAR=testtest >> rd.live.overlay/etc/conf.d/testvar.conf
# tree rd.live.overlay/
rd.live.overlay/
`-- etc
    |-- cmdline.d
    |   `-- mycmdline.conf
    `-- 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.


[[NetworkBoot]]
=== 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
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/[Red
Hat Enterprise Linux Storage Administration Guide].

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 <<Injecting>>.

==== 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]]
=== Identifying your problem area
. Remove ''rhgb'' and ''quiet'' from the kernel command line
. Add ''rd.shell'' to the kernel command line. This will present a shell should
dracut be unable to locate your root device
. Add ''rd.shell rd.debug log_buf_len=1M'' to the kernel command line so that
dracut shell commands are printed as they are executed
. 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]]
=== Information to include in your report

[[all-bug-reports]]
==== 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]]
==== 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 <<all-bug-reports>>, include the
following information:


* Please include the output of
+
----
# /sbin/ifup <interfacename>
# ip addr show
----

[[debugging-dracut]]
=== Debugging dracut


[[configure-a-serial-console]]
==== 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.

. 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
----
+
. 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]]
==== 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 ''rd.shell'' to your bootloader configuration file
(e.g. _/boot/grub2/grub.cfg_ (or _/boot/efi/EFI/redhat/grub.cfg_ for EFI systems))
. Remove the boot arguments ''rhgb'' and ''quiet''
+
A sample _grub.cfg_ bootloader configuration file snippet is listed below.
+
----
menuentry 'Red Hat Enterprise Linux Server (3.10.0-308.el7.x86_64) 7.0 (Maipo)' […] {
  […]
  linux16 /vmlinuz-3.10.0-308.el7.x86_64 ro root=/dev/mapper/vg_uc1-lv_root console=tty0 rd.shell
  initrd16 /initramfs-3.10.0-308.el7.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.

#
----
+
. Use this shell prompt to gather the information requested above
(see <<all-bug-reports>>).

[[accessing-the-root-volume-from-the-dracut-shell]]
==== 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.

. 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]]
==== Additional dracut boot parameters
For more debugging options, see *dracut.cmdline*(7).


[[debugging-dracut-on-shutdown]]
==== 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.