diff options
| -rw-r--r-- | documentation/ref-manual/terms.rst | 42 | ||||
| -rw-r--r-- | documentation/ref-manual/variables.rst | 42 |
2 files changed, 42 insertions, 42 deletions
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: | |||
| 212 | of the supported image types that the Yocto Project provides, see the | 212 | of the supported image types that the Yocto Project provides, see the |
| 213 | ":ref:`ref-manual/images:Images`" chapter. | 213 | ":ref:`ref-manual/images:Images`" chapter. |
| 214 | 214 | ||
| 215 | :term:`Initramfs` | ||
| 216 | An Initial RAM Filesystem (:term:`Initramfs`) is an optionally compressed | ||
| 217 | :wikipedia:`cpio <Cpio>` archive which is extracted | ||
| 218 | by the Linux kernel into RAM in a special :wikipedia:`tmpfs <Tmpfs>` | ||
| 219 | instance, used as the initial root filesystem. | ||
| 220 | |||
| 221 | This is a replacement for the legacy init RAM disk ("initrd") | ||
| 222 | technique, booting on an emulated block device in RAM, but being less | ||
| 223 | efficient because of the overhead of going through a filesystem and | ||
| 224 | having to duplicate accessed file contents in the file cache in RAM, | ||
| 225 | as for any block device. | ||
| 226 | |||
| 227 | .. note: | ||
| 228 | |||
| 229 | As far as bootloaders are concerned, :term:`Initramfs` and "initrd" | ||
| 230 | images are still copied to RAM in the same way. That's why most | ||
| 231 | most bootloaders refer to :term:`Initramfs` images as "initrd" | ||
| 232 | or "init RAM disk". | ||
| 233 | |||
| 234 | This kind of mechanism is typically used for two reasons: | ||
| 235 | |||
| 236 | - For booting the same kernel binary on multiple systems requiring | ||
| 237 | different device drivers. The :term:`Initramfs` image is then customized | ||
| 238 | for each type of system, to include the specific kernel modules | ||
| 239 | necessary to access the final root filesystem. This technique | ||
| 240 | is used on all GNU / Linux distributions for desktops and servers. | ||
| 241 | |||
| 242 | - For booting faster. As the root filesystem is extracted into RAM, | ||
| 243 | accessing the first user-space applications is very fast, compared | ||
| 244 | to having to initialize a block device, to access multiple blocks | ||
| 245 | from it, and to go through a filesystem having its own overhead. | ||
| 246 | For example, this allows to display a splashscreen very early, | ||
| 247 | and to later take care of mounting the final root filesystem and | ||
| 248 | loading less time-critical kernel drivers. | ||
| 249 | |||
| 250 | This cpio archive can either be loaded to RAM by the bootloader, | ||
| 251 | or be included in the kernel binary. | ||
| 252 | |||
| 253 | For information on creating and using an :term:`Initramfs`, see the | ||
| 254 | ":ref:`dev-manual/building:building an initial ram filesystem (Initramfs) image`" | ||
| 255 | section in the Yocto Project Development Tasks Manual. | ||
| 256 | |||
| 215 | :term:`Layer` | 257 | :term:`Layer` |
| 216 | A collection of related recipes. Layers allow you to consolidate related | 258 | A collection of related recipes. Layers allow you to consolidate related |
| 217 | metadata to customize your build. Layers also isolate information used | 259 | 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. | |||
| 3956 | even if the toolchain's binaries are strippable, there are other files | 3956 | even if the toolchain's binaries are strippable, there are other files |
| 3957 | needed for the build that are not strippable. | 3957 | needed for the build that are not strippable. |
| 3958 | 3958 | ||
| 3959 | :term:`Initramfs` | ||
| 3960 | An Initial RAM Filesystem (:term:`Initramfs`) is an optionally compressed | ||
| 3961 | :wikipedia:`cpio <Cpio>` archive which is extracted | ||
| 3962 | by the Linux kernel into RAM in a special :wikipedia:`tmpfs <Tmpfs>` | ||
| 3963 | instance, used as the initial root filesystem. | ||
| 3964 | |||
| 3965 | This is a replacement for the legacy init RAM disk ("initrd") | ||
| 3966 | technique, booting on an emulated block device in RAM, but being less | ||
| 3967 | efficient because of the overhead of going through a filesystem and | ||
| 3968 | having to duplicate accessed file contents in the file cache in RAM, | ||
| 3969 | as for any block device. | ||
| 3970 | |||
| 3971 | .. note: | ||
| 3972 | |||
| 3973 | As far as bootloaders are concerned, :term:`Initramfs` and "initrd" | ||
| 3974 | images are still copied to RAM in the same way. That's why most | ||
| 3975 | most bootloaders refer to :term:`Initramfs` images as "initrd" | ||
| 3976 | or "init RAM disk". | ||
| 3977 | |||
| 3978 | This kind of mechanism is typically used for two reasons: | ||
| 3979 | |||
| 3980 | - For booting the same kernel binary on multiple systems requiring | ||
| 3981 | different device drivers. The :term:`Initramfs` image is then customized | ||
| 3982 | for each type of system, to include the specific kernel modules | ||
| 3983 | necessary to access the final root filesystem. This technique | ||
| 3984 | is used on all GNU / Linux distributions for desktops and servers. | ||
| 3985 | |||
| 3986 | - For booting faster. As the root filesystem is extracted into RAM, | ||
| 3987 | accessing the first user-space applications is very fast, compared | ||
| 3988 | to having to initialize a block device, to access multiple blocks | ||
| 3989 | from it, and to go through a filesystem having its own overhead. | ||
| 3990 | For example, this allows to display a splashscreen very early, | ||
| 3991 | and to later take care of mounting the final root filesystem and | ||
| 3992 | loading less time-critical kernel drivers. | ||
| 3993 | |||
| 3994 | This cpio archive can either be loaded to RAM by the bootloader, | ||
| 3995 | or be included in the kernel binary. | ||
| 3996 | |||
| 3997 | For information on creating and using an :term:`Initramfs`, see the | ||
| 3998 | ":ref:`dev-manual/building:building an initial ram filesystem (Initramfs) image`" | ||
| 3999 | section in the Yocto Project Development Tasks Manual. | ||
| 4000 | |||
| 4001 | :term:`INITRAMFS_DEPLOY_DIR_IMAGE` | 3959 | :term:`INITRAMFS_DEPLOY_DIR_IMAGE` |
| 4002 | Indicates the deploy directory used by :ref:`ref-tasks-bundle_initramfs` | 3960 | Indicates the deploy directory used by :ref:`ref-tasks-bundle_initramfs` |
| 4003 | where the :term:`INITRAMFS_IMAGE` will be fetched from. This variable is | 3961 | where the :term:`INITRAMFS_IMAGE` will be fetched from. This variable is |
