From 43bf0b2a10bc8f312ad4b38649c8523620d66d2b Mon Sep 17 00:00:00 2001 From: Glenn Washburn Date: Tue, 1 Aug 2023 19:58:51 -0500 Subject: [PATCH] docs: Improve initrd documentation 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 Reviewed-by: Oskari Pirhonen Reviewed-by: Paul Menzel Reviewed-by: Daniel Kiper --- docs/grub.texi | 48 +++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 41 insertions(+), 7 deletions(-) diff --git a/docs/grub.texi b/docs/grub.texi index b233e28e0..be2261670 100644 --- a/docs/grub.texi +++ b/docs/grub.texi @@ -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