dracut
======
Harald Hoyer <harald@redhat.com>
-v2.0, March 2011
+v3.0, October 2013
:language: bash
== Dracut on shutdown
-On a systemd driven system, the dracut initramfs is also used for the shutdown procedure.
+On a systemd driven system, the dracut initramfs is also used for the shutdown
+procedure.
The following steps are executed during a shutdown:
* systemd switches to the shutdown.target
-* systemd starts /lib/systemd/system/shutdown.target.wants/dracut-shutdown.service
+* systemd starts
+ $prefix/lib/systemd/system/shutdown.target.wants/dracut-shutdown.service
* dracut-shutdown.service executes /usr/lib/dracut/dracut-initramfs-restore
which unpacks the initramfs to /run/initramfs
* systemd finishes shutdown.target
* systemd tries to unmount everything and mounts the remaining read-only
* systemd checks, if there is a /run/initramfs/shutdown executable
* if yes, it does a pivot_root to /run/initramfs and executes ./shutdown.
- The old root is then mounted on /oldroot. /usr/lib/dracut/modules.d/99shutdown/shutdown.sh is the shutdown executable.
-* shutdown will try to umount every /oldroot mount and calls the various shutdown hooks from the dracut modules
+ The old root is then mounted on /oldroot.
+ /usr/lib/dracut/modules.d/99shutdown/shutdown.sh is the shutdown executable.
+* shutdown will try to umount every /oldroot mount and calls the various
+ shutdown hooks from the dracut modules
This ensures, that all devices are disassembled and unmounted cleanly.
= User Manual
-== Creating an initramfs Image
-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 --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 <<dracutconf5>>.
-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
-----
-
-or, if you have a dracut version earlier than +008+, issue the command:
-----
-# for mod in /usr/lib/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 <<dracutconf5>>), 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 <<dracutconf5>>):
-----
-# dracut --add-drivers mymod initramfs-with-mymod.img
-----
-
-== 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 <<NetworkBoot>>.
-
-For a full reference of all kernel command line parameters, see <<dracut8>>.
-
-=== 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:
-----
-vconsole.font=latarcyrheb-sun16 vconsole.keymap=de-latin1-nodeadkeys 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.
-
-For dracut versions prior to version +008+ the line would look like:
-----
-LANG=de_DE.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=de-latin1-nodeadkeys
-----
-
-=== 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
-----
-
-On systems with dracut version prior to +008+ the line would look like:
-----
-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]]
-=== 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 rd.live.overlay
-# mkdir rd.live.overlay/etc
-# mkdir rd.live.overlay/etc/conf.d
-# mkdir rd.live.overlay/etc/cmdline.d
-# echo "ip=auto" >> 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=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.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.
-
-
-
-=== NFS Root Device
-
-FIXME
-
-=== iSCSI Root Device
-
-FIXME
-
-=== FCoE Root Device
-
-FIXME
-
-== 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
-. With dracut >= 002-11, you can inspect the rd.debug output with:
-+
-----
-# less /run/initramfs/init.log
-# dmesg | less
-----
-. With dracut >= 022 and systemd, you can inspect the rd.debug output with:
-----
-# journalctl -ab
-----
-. With dracut >= 025 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. _/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. 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]]
-==== Logical Volume Management related problems
-As well as the information from <<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]]
-==== Software RAID related problems
-As well as the information from <<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]]
-==== 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.
-
-. 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
-+
---
-NOTE: 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]]
-==== 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. _/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 rd.shell
- 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.
-
-#
-----
-+
-. 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.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]]
-==== Additional dracut boot parameters
-For more debugging options, see <<dracutkerneldebug>> in <<dracutcmdline7>>.
-
-= Developer Manual
-
-== dracut Components
-
-dracut uses a modular system to build and extend the initramfs image. All
-modules are located in _/usr/lib/dracut/modules.d_ or in _<git-src>/modules.d_.
-The most basic dracut module is _99base_. In _99base_ the initial shell script
-init is defined, which gets run by the kernel after initramfs loading. Although
-you can replace init with your own version of _99base_, this is not encouraged.
-Instead you should use, if possible, the hooks of dracut. All hooks, and the
-point of time in which they are executed, are described in <<stages>>.
-
-The main script, which creates the initramfs is dracut itsself. It parses all
-arguments and sets up the directory, in which everything is installed. It then
-executes all check, install, installkernel scripts found in the modules, which
-are to be processed. After everything is installed, the install directory is
-archived and compressed to the final initramfs image. All helper functions used
-by check, install and installkernel are found in in the file _dracut-functions_.
-These shell functions are available to all module installer (install,
-installkernel) scripts, without the need to source _dracut-functions_.
-
-A module can check the preconditions for install and installkernel with the
-check script. Also dependencies can be expressed with check. If a module passed
-check, install and installkernel will be called to install all of the necessary
-files for the module. To split between kernel and non-kernel parts of the
-installation, all kernel module related parts have to be in installkernel. All
-other files found in a module directory are module specific and mostly are hook
-scripts and udev rules.
-
-
-[[stages]]
-== Boot Process Stages
-
-dracut modules can insert custom script at various points, to control the boot
-process.
-These hooks are plain directories containing shell scripts ending with ".sh",
-which are sourced by init.
-Common used functions are in _dracut-lib.sh_, which can be sourced by any script.
-
-=== Hook: cmdline
-
-The _cmdline_ hook is a place to insert scripts to parse the kernel command line
-and prepare the later actions, like setting up udev rules and configuration
-files.
-
-In this hook the most important environment variable is defined: root. The
-second one is rootok, which indicates, that a module claimed to be able to parse
-the root defined. So for example, **root=**__iscsi:....__ will be claimed by the
-iscsi dracut module, which then sets rootok.
-
-=== Hook: pre-udev
-
-This hook is executed right after the cmdline hook and a check if root and
-rootok were set. Here modules can take action with the final root, and before
-udev has been run.
-
-=== Start Udev
-
-Now udev is started and the logging for udev is setup.
-
-=== Hook: pre-trigger
-
-In this hook, you can set udev environment variables with **udevadm control
---property=KEY=_value_** or control the further execution of udev with
-udevadm.
-
-=== Trigger Udev
-
-udev is triggered by calling udevadm trigger, which sends add events for all
-devices and subsystems.
-
-=== Main Loop
-
-In the main loop of dracut loops until udev has settled and
-all scripts in _initqueue/finished_ returned true.
-In this loop there are three hooks, where scripts can be inserted
-by calling /sbin/initqueue.
-
-==== Initqueue
-
-This hook gets executed every time a script is inserted here, regardless of the
-udev state.
-
-==== Initqueue settled
-
-This hooks (initqueue/settled) gets executed every time udev has settled.
-
-
-==== Initqueue timeout
-
-This hooks (initqueue/timeout) gets executed, when the main loop counter becomes half of the
-rd.retry counter.
-
-==== Initqueue finished
-
-This hook (initqueue/finished) is called after udev has settled and
-if all scripts herein return 0 the main loop will be ended.
-Abritary scripts can be added here, to loop in the
-initqueue until something happens, which a dracut module wants to wait for.
-
-=== Hook: pre-mount
-
-Before the root device is mounted all scripts in the hook pre-mount are
-executed. In some cases (e.g. NFS) the real root device is already mounted,
-though.
-
-=== Hook: mount
-
-This hook is mainly to mount the real root device.
-
-=== Hook: pre-pivot
-
-This hook is called before cleanup hook, This is a good place for
-actions other than cleanups which need to be called before pivot.
-
-=== Hook: cleanup
-
-This hook is the last hook and is called before init finally switches root to
-the real root device. This is a good place to clean up and kill processes not
-needed anymore.
-
-
-=== Cleanup and switch_root
-
-Init (or systemd) kills all udev processes, cleans up the environment,
-sets up the arguments for the real init process and finally calls switch_root.
-switch_root removes the whole filesystem hierarchy of the initramfs,
-chroot()s to the real root device and calls /sbin/init with the specified arguments.
-
-To ensure all files in the initramfs hierarchy can be removed, all processes
-still running from the initramfs should not have any open file descriptors left.
-
-== Network Infrastructure
-
-FIXME
-
-== Writing a Module
-
-A simple example module is _96insmodpost_, which modprobes a kernel module after
-udev has settled and the basic device drivers have been loaded.
-
-All module installation information is in the file module-setup.sh.
-
-First we create a check() function, which just exits with 0 indicating that this
-module should be included by default.
-
-check():
-----
-return 0
-----
-
-The we create the install() function, which installs a cmdline hook with
-priority number 20 called _parse-insmodpost.sh_. It also installs the
-_insmodpost.sh_ script in _/sbin_.
-
-install():
-----
-inst_hook cmdline 20 "$moddir/parse-insmodpost.sh"
-inst_simple "$moddir/insmodpost.sh" /sbin/insmodpost.sh
-----
-
-The _pase-instmodpost.sh_ parses the kernel command line for a argument
-rd.driver.post, blacklists the module from being autoloaded and installs the
-hook _insmodpost.sh_ in the _initqueue/settled_.
-
-_parse-insmodpost.sh_:
-----
-for p in $(getargs rd.driver.post=); do
- echo "blacklist $p" >> /etc/modprobe.d/initramfsblacklist.conf
- _do_insmodpost=1
-done
-
-[ -n "$_do_insmodpost" ] && /sbin/initqueue --settled --unique --onetime /sbin/insmodpost.sh
-unset _do_insmodpost
-
-----
-
-_insmodpost.sh_, which is called in the _initqueue/settled_ hook will just
-modprobe the kernel modules specified in all rd.driver.post kernel command line
-parameters. It runs after udev has settled and is only called once (--onetime).
-
-_insmodpost.sh_:
-----
-. /lib/dracut-lib.sh
-
-for p in $(getargs rd.driver.post=); do
- modprobe $p
-done
-
-----
-
-
-
-=== check()
-
-_check()_ is called by dracut to evaluate the inclusion of a dracut module in
-the initramfs.
-
-$hostonly:: If the $hostonly variable is set, then the module check() function
-should be in "hostonly" mode, which means, that the check() should only return
-0, if the module is really needed to boot this specific host.
-
-check() should return with:
-
-0:: Include the dracut module in the initramfs.
-
-1:: Do not include the dracut module. The requirements are not fullfilled
-(missing tools, etc.)
-
-255:: Only include the dracut module, if another module requires it or if
-explicitly specified in the config file or on the argument list.
-
-
-
-=== depends()
-
-The function depends() should echo all other dracut module names the module
-depends on.
-
-
-
-=== install()
-
-inst_multiple
-
-inst
-
-inst_hook
-
-inst_rules
-
-
-
-
-
-=== installkernel()
-
-instmods
-
-
-
-=== Creation Functions
-
-FIXME
-
-
-=== Initramfs Functions
-
-FIXME
-
-
-=== Network Modules
-
-FIXME
-
:leveloffset: 1
-[[dracutbootup7]]
-include::dracut.bootup.7.asc[]
-
-:leveloffset: 1
-[[dracut8]]
include::dracut.8.asc[]
+:leveloffset: 1
[[dracutconf5]]
include::dracut.conf.5.asc[]
[[mkinitrd8]]
include::mkinitrd.8.asc[]
+= Developer Manual
+
+:leveloffset: 1
+[[dracutmodules7]]
+include::dracut.modules.7.asc[]
+
+[[dracutbootup7]]
+include::dracut.bootup.7.asc[]
+
:leveloffset: 0
[appendix]
License
projects / thirdparty / dracut.git / blobdiff