doc: Add "Initial RAM Disk" section.
* doc/guix.texi (Initial RAM Disk): New node. * gnu/system/linux-initrd.scm (expression->initrd): Adjust docstring.
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Ludovic Courtès
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@ -2847,6 +2847,7 @@ instance to support new system services.
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* File Systems:: Configuring file system mounts.
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* User Accounts:: Specifying user accounts.
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* Services:: Specifying system services.
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* Initial RAM Disk:: Linux-Libre bootstrapping.
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* Invoking guix system:: Instantiating a system configuration.
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* Defining Services:: Adding new service definitions.
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@end menu
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@ -3259,6 +3260,76 @@ password. When @var{auto-login?} is true, log in automatically as
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@end deffn
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@node Initial RAM Disk
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@subsection Initial RAM Disk
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@cindex initial RAM disk (initrd)
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@cindex initrd (initial RAM disk)
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For bootstrapping purposes, the Linux-Libre kernel is passed an
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@dfn{initial RAM disk}, or @dfn{initrd}. An initrd contains a temporary
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root file system, as well as an initialization script. The latter is
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responsible for mounting the real root file system, and for loading any
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kernel modules that may be needed to achieve that.
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The @code{initrd} field of an @code{operating-system} declaration allows
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you to specify which initrd you would like to use. The @code{(gnu
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system linux-initrd)} module provides two ways to build an initrd: the
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high-level @code{base-initrd} procedure, and the low-level
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@code{expression->initrd} procedure.
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The @code{base-initrd} procedure is intended to cover most common uses.
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For example, if you want to add a bunch of kernel modules to be loaded
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at boot time, you can define the @code{initrd} field of the operating
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system declaration like this:
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@example
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(initrd (cut base-init <>
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#:extra-modules '("my.ko" "modules.ko")))
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@end example
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It also handles common use cases that involves using the system as a
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QEMU guest, or as a ``live'' system whose root file system is volatile.
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@deffn {Monadic Procedure} base-initrd @var{file-systems} @
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[#:qemu-networking? #f] [#:virtio? #f] [#:volatile-root? #f] @
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[#:extra-modules '()]
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Return a monadic derivation that builds a generic initrd. @var{file-systems} is
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a list of file-systems to be mounted by the initrd, possibly in addition to
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the root file system specified on the kernel command line via @code{--root}.
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When @var{qemu-networking?} is true, set up networking with the standard QEMU
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parameters. When @var{virtio?} is true, load additional modules so the initrd can
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be used as a QEMU guest with para-virtualized I/O drivers.
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When @var{volatile-root?} is true, the root file system is writable but any changes
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to it are lost.
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The initrd is automatically populated with all the kernel modules necessary
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for @var{file-systems} and for the given options. However, additional kernel
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modules can be listed in @var{extra-modules}. They will be added to the initrd, and
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loaded at boot time in the order in which they appear.
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@end deffn
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Needless to say, the initrds we produce and use embed a
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statically-linked Guile, and the initialization program is a Guile
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program. That gives a lot of flexibility. The
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@code{expression->initrd} procedure builds such an initrd, given the
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program to run in that initrd.
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@deffn {Monadic Procedure} expression->initrd @var{exp} @
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[#:guile %guile-static-stripped] [#:name "guile-initrd"] @
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[#:modules '()] [#:to-copy '()] [#:linux #f] @
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[#:linux-modules '()]
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Return a derivation that builds a Linux initrd (a gzipped cpio archive)
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containing @var{guile} and that evaluates @var{exp}, a G-expression,
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upon booting.
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@var{linux-modules} is a list of @file{.ko} file names to be copied from
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@var{linux} into the initrd. @var{to-copy} is a list of additional
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derivations or packages to copy to the initrd. @var{modules} is a list
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of Guile module names to be embedded in the initrd.
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@end deffn
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@node Invoking guix system
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@subsection Invoking @code{guix system}
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@ -57,11 +57,13 @@
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(to-copy '())
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(linux #f)
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(linux-modules '()))
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"Return a package that contains a Linux initrd (a gzipped cpio archive)
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containing GUILE and that evaluates EXP upon booting. LINUX-MODULES is a list
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of `.ko' file names to be copied from LINUX into the initrd. TO-COPY is a
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list of additional derivations or packages to copy to the initrd. MODULES is
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a list of Guile module names to be embedded in the initrd."
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"Return a derivation that builds a Linux initrd (a gzipped cpio archive)
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containing GUILE and that evaluates EXP, a G-expression, upon booting.
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LINUX-MODULES is a list of '.ko' file names to be copied from LINUX into the
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initrd. TO-COPY is a list of additional derivations or packages to copy to
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the initrd. MODULES is a list of Guile module names to be embedded in the
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initrd."
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;; General Linux overview in `Documentation/early-userspace/README' and
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;; `Documentation/filesystems/ramfs-rootfs-initramfs.txt'.
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