1 Most of the functionality that dracut implements are actually implemented
2 by dracut modules. Dracut modules live in modules.d, and have the following
5 dracut_install_dir/modules.d/
9 <other files as needed by the hook>
11 00modname: The name of the module prefixed by a two-digit numeric sort code.
12 The numeric code must be present and in the range of 00 - 99.
13 Modules with lower numbers are installed first. This is important
14 because the dracut install functions (which install files onto
15 the initrd) refuse to overwrite already installed files. This makes
16 it easy for an earlier module to override the functionality of a
17 later module, so that you can have a distro or system specific
18 module override or modify the functionality of a generic module
19 without having to patch the more generic module.
22 dracut sources this script to install the functionality that a
23 module implements onto the initrd. For the most part, this amounts
24 to copying files from the host system onto the initrd in a controlled
28 This function of module-setup.sh is called to install all
29 non-kernel files. dracut supplies several install functions that are
30 specialized for different file types. Browse through dracut-functions
31 fore more details. dracut also provides a $moddir variable if you
32 need to install a file from the module directory, such as an initrd
33 hook, a udev rule, or a specialized executable.
36 This function of module-setup.sh is called to install all
41 Dracut calls this function to check and see if a module can be installed
44 When called without options, check should check to make sure that
45 any files it needs to install into the initrd from the host system
46 are present. It should exit with a 0 if they are, and a 1 if they are
49 When called with $hostonly set, it should perform the same check
50 that it would without it set, and it should also check to see if the
51 functionality the module implements is being used on the host system.
52 For example, if this module handles installing support for LUKS
53 encrypted volumes, it should return 0 if all the tools to handle
54 encrpted volumes are available and the host system has the root
55 partition on an encrypted volume, 1 otherwise.
58 This function should output a list of dracut modules
59 that it relies upon. An example would be the nfs and iscsi modules,
60 which rely on the network module to detect and configure network
63 Any other files in the module will not be touched by dracut directly.
65 You are encouraged to provide a README that describes what the module is for.
71 init has the following hook points to inject scripts:
73 /lib/dracut/hooks/cmdline/*.sh
74 scripts for command line parsing
76 /lib/dracut/hooks/pre-udev/*.sh
77 scripts to run before udev is started
79 /lib/dracut/hooks/pre-trigger/*.sh
80 scripts to run before the main udev trigger is pulled
82 /lib/dracut/hooks/initqueue/*.sh
83 runs in parallel to the udev trigger
84 Udev events can add scripts here with /sbin/initqueue.
85 If /sbin/initqueue is called with the "--onetime" option, the script
86 will be removed after it was run.
87 If /lib/dracut/hooks/initqueue/work is created and udev >= 143 then
88 this loop can process the jobs in parallel to the udevtrigger.
89 If the udev queue is empty and no root device is found or no root
90 filesystem was mounted, the user will be dropped to a shell after
92 Scripts can remove themselves from the initqueue by "rm $job".
94 /lib/dracut/hooks/pre-mount/*.sh
95 scripts to run before the root filesystem is mounted
96 Network filesystems like NFS that do not use device files are an
97 exception. Root can be mounted already at this point.
99 /lib/dracut/hooks/mount/*.sh
100 scripts to mount the root filesystem
101 If the udev queue is empty and no root device is found or no root
102 filesystem was mounted, the user will be dropped to a shell after
105 /lib/dracut/hooks/pre-pivot/*.sh
106 scripts to run before latter initramfs cleanups
108 /lib/dracut/hooks/pre-pivot-cleanup/*.sh
109 scripts to run before the real init is executed and the initramfs
111 All processes started before should be killed here.