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docs: Improve initrd documentation

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A list of improvements:
  * Remove reference to "initial ramdisk" and replace with "initrd". This
    then covers the case of ramdisk and ramfs, which is the usual method
    with kernels 2.6 and newer.
  * Add sentence with URL to initrd documentation Linux kernel.
  * Add a section documenting how to have the initrd command generate
    a new-style initrd via a specially crafted argument and include an example.
  * Update initrd16 to refer to the initrd section and make note that
    initrd16 is only on the pc platform.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Oskari Pirhonen <xxc3ncoredxx@gmail.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Glenn Washburn 2023-08-01 19:58:51 -05:00 committed by Daniel Kiper
parent b0890d371c
commit 43bf0b2a10
1 changed files with 41 additions and 7 deletions
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docs/grub.texi
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@ -4068,10 +4068,43 @@ load a defective boot loader, such as SCO UnixWare 7.1.
@subsection initrd
@deffn Command initrd file [file @dots{}]
Load, in order, all initial ramdisks for a Linux kernel image, and set
the appropriate parameters in the Linux setup area in memory. This may only
be used after the @command{linux} command (@pxref{linux}) has been run. See
also @ref{GNU/Linux}.
Load, in order, all initrds for a Linux kernel image, and set the
appropriate parameters in the Linux setup area in memory. This may only
be used after the @command{linux} command (@pxref{linux}) has been run.
See @ref{GNU/Linux} for more info on booting GNU/Linux. For more
information on initrds see the GNU/Linux kernel
@uref{https://docs.kernel.org/filesystems/ramfs-rootfs-initramfs.html,
documentation}.
A new-style initrd (for kernels newer than 2.6) containing one file
with leading path components can also be generated at run time. This
can be done by prefixing an argument with @code{newc:} followed by the
path of the file in the new initrd, a @code{:}, and then the GRUB file
path to the file data to be be included.
For example:
@example
initrd newc:/etc/ssh/config:(hd0,2)/home/user/.ssh/config \
newc:/etc/ssh/ssh_host_rsa_key:/etc/ssh/ssh_host_rsa_key \
/boot/initrd.gz \
newc:/init:/home/user/init.fixed
@end example
This command will generate two new-style initrds on the fly. The first
contains the path @samp{/etc/ssh/config} with the contents of
@samp{(hd0,2)/home/user/.ssh/config} and the path
@samp{/etc/ssh/ssh_host_rsa_key} with the contents of
@samp{/etc/ssh/ssh_host_rsa_key} on the @var{root} device. Parent directory
paths will automatically be generated as needed. This first generated initrd
will then have @samp{/boot/initrd.gz} concatenated after it. Next, another
new-style archive will be generated with the contents of @samp{/home/user/init.fixed}
in the path @samp{/init} and appended to the previous concatenation. Finally,
the result will be sent to the kernel when booted.
Keep in mind that paths that come later will take precedence. So in the
example above, the generated path @samp{/init} will overwrite any @samp{/init}
in @samp{/boot/initrd.gz}. This can be useful when changing the main initrd
is undesirable or difficult.
@end deffn
@ -4079,12 +4112,13 @@ also @ref{GNU/Linux}.
@subsection initrd16
@deffn Command initrd16 file [file @dots{}]
Load, in order, all initial ramdisks for a Linux kernel image to be booted in
Load, in order, all initrds for a Linux kernel image to be booted in
16-bit mode, and set the appropriate parameters in the Linux setup area in
memory. This may only be used after the @command{linux16} command
(@pxref{linux16}) has been run. See also @ref{GNU/Linux}.
(@pxref{linux16}) has been run. See also @ref{GNU/Linux} and the @command{initrd}
command (@pxref{initrd}) for more details on arguments.
This command is only available on x86 systems.
This command is only available on the pc platform for x86 systems.
@end deffn