Dracut is the tool used by desktop distributions to build initrds.
In the embedded world, it can be very useful, too, for instance when
wanting to create an initramfs for a system recovery mode.
Whereas it is definitively possible to achieve this with buildroot, the
process is to have a dedicated buildroot configuration for that, and
perform a full build. Instead of doing that, dracut can pick the needed
binaries/shared libraries, configuration files, or kernel modules from
the 'target' directory.
The advantage is to save build time, and also to have a consistency
between the packages versions taken for the recovery and the production
filesystem.
The principle of dracut is based on the so-called 'dracut modules'. The
modules determine what will be included in the initramfs. For example,
one of dracut's modules checks the kernel modules that are included and
also includes the corresponding firmware blobs.
On the host, they are on host/lib/dracut/modules.d
Each directory as a prefix number for the order of execution, and
at least a "module-setup.sh" script.
Dracut sources all of them, and typically calls the "check()" function,
which is the placeholder for required binaries (that are aimed to be
polulated in the initrd), then the "depends()" function, that lists
other modules to depend on, and the "install()" function, that makes
the actual work.
Dracut was initially thought to work with systems using systemd,
but it can also work without it. Do to so, every "systemd-xxx"
module must be disabled in the dracut configuration file. For
convenience, the 05busybox-init module is provided, to support
busybox init system. Note that this module should *not* be enabled when
using systemd init. It is therefore only installed if busybox init is
selected.
Musl and uClibc make assumptions about the existence of some symlinks
that are not discoverable with readelf. Therefore, another module
05libc-links is provided that creates those links. The module is
installed regardless of which libc is used - the script itself discovers
if the links need to be installed based on which libc is found.
Signed-off-by: Thierry Bultel <thierry.bultel@linatsea.fr>
[arnout@mind.be: many changes]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Adam Duskett <aduskett@gmail.com>
[yann.morin.1998@free.fr: some additional fixups]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
87f4900826