diff --git a/documentation/ref-manual/terms.rst b/documentation/ref-manual/terms.rst index 92cc723ff6..68313d0294 100644 --- a/documentation/ref-manual/terms.rst +++ b/documentation/ref-manual/terms.rst @@ -212,6 +212,48 @@ universal, the list includes them just in case: of the supported image types that the Yocto Project provides, see the ":ref:`ref-manual/images:Images`" chapter. + :term:`Initramfs` + An Initial RAM Filesystem (:term:`Initramfs`) is an optionally compressed + :wikipedia:`cpio ` archive which is extracted + by the Linux kernel into RAM in a special :wikipedia:`tmpfs ` + instance, used as the initial root filesystem. + + This is a replacement for the legacy init RAM disk ("initrd") + technique, booting on an emulated block device in RAM, but being less + efficient because of the overhead of going through a filesystem and + having to duplicate accessed file contents in the file cache in RAM, + as for any block device. + + .. note: + + As far as bootloaders are concerned, :term:`Initramfs` and "initrd" + images are still copied to RAM in the same way. That's why most + most bootloaders refer to :term:`Initramfs` images as "initrd" + or "init RAM disk". + + This kind of mechanism is typically used for two reasons: + + - For booting the same kernel binary on multiple systems requiring + different device drivers. The :term:`Initramfs` image is then customized + for each type of system, to include the specific kernel modules + necessary to access the final root filesystem. This technique + is used on all GNU / Linux distributions for desktops and servers. + + - For booting faster. As the root filesystem is extracted into RAM, + accessing the first user-space applications is very fast, compared + to having to initialize a block device, to access multiple blocks + from it, and to go through a filesystem having its own overhead. + For example, this allows to display a splashscreen very early, + and to later take care of mounting the final root filesystem and + loading less time-critical kernel drivers. + + This cpio archive can either be loaded to RAM by the bootloader, + or be included in the kernel binary. + + For information on creating and using an :term:`Initramfs`, see the + ":ref:`dev-manual/building:building an initial ram filesystem (Initramfs) image`" + section in the Yocto Project Development Tasks Manual. + :term:`Layer` A collection of related recipes. Layers allow you to consolidate related metadata to customize your build. Layers also isolate information used diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst index 86ffd8912d..bfdf1d1401 100644 --- a/documentation/ref-manual/variables.rst +++ b/documentation/ref-manual/variables.rst @@ -3956,48 +3956,6 @@ system and gives an overview of their function and contents. even if the toolchain's binaries are strippable, there are other files needed for the build that are not strippable. - :term:`Initramfs` - An Initial RAM Filesystem (:term:`Initramfs`) is an optionally compressed - :wikipedia:`cpio ` archive which is extracted - by the Linux kernel into RAM in a special :wikipedia:`tmpfs ` - instance, used as the initial root filesystem. - - This is a replacement for the legacy init RAM disk ("initrd") - technique, booting on an emulated block device in RAM, but being less - efficient because of the overhead of going through a filesystem and - having to duplicate accessed file contents in the file cache in RAM, - as for any block device. - - .. note: - - As far as bootloaders are concerned, :term:`Initramfs` and "initrd" - images are still copied to RAM in the same way. That's why most - most bootloaders refer to :term:`Initramfs` images as "initrd" - or "init RAM disk". - - This kind of mechanism is typically used for two reasons: - - - For booting the same kernel binary on multiple systems requiring - different device drivers. The :term:`Initramfs` image is then customized - for each type of system, to include the specific kernel modules - necessary to access the final root filesystem. This technique - is used on all GNU / Linux distributions for desktops and servers. - - - For booting faster. As the root filesystem is extracted into RAM, - accessing the first user-space applications is very fast, compared - to having to initialize a block device, to access multiple blocks - from it, and to go through a filesystem having its own overhead. - For example, this allows to display a splashscreen very early, - and to later take care of mounting the final root filesystem and - loading less time-critical kernel drivers. - - This cpio archive can either be loaded to RAM by the bootloader, - or be included in the kernel binary. - - For information on creating and using an :term:`Initramfs`, see the - ":ref:`dev-manual/building:building an initial ram filesystem (Initramfs) image`" - section in the Yocto Project Development Tasks Manual. - :term:`INITRAMFS_DEPLOY_DIR_IMAGE` Indicates the deploy directory used by :ref:`ref-tasks-bundle_initramfs` where the :term:`INITRAMFS_IMAGE` will be fetched from. This variable is