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Re: [gentoo-dev] New News Item v2: 2026-xx-yy-dracut-hostonly-cmdline

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Nowa Ammerlaan <nowa@gentoo.org> writes:

> Hi Team,
>
> Here's v2 of the news item after feedback from Immolo and Sam.
>
> @Sam, in this version I have added a list of relevant files for each
> possible setup directly below the section header. I think this helps
> to make it more clear at a single glance where users have to look to
> verify and set the cmdline. Together with a general comment about
> 'lsinitrd' in an earlier paragraph this might help to navigate the
> instructions quicker. Is this sort of what you meant?
>
> I have also changed:
> - the order of systemd-boot and GRUB
> - Added instructions on how to check if secureboot is enabled
> - formatting (more and less '='s where relevant)
> - Added a general note about lsinitrd in the all-users section
> - rescue CD or USB -> rescue media
>
> Best regards,
> Nowa

Thanks, I think this is getting there. I reviewed most of it but needed
to get on with some other things, but hopefully the suggestions so far
are enough to get the idea, and I can come back and do the rest then.

>
>
> Title: Dracut changed default for hostonly_cmdline setting
> Author: Nowa Ammerlaan <nowa@gentoo.org>
> Posted: 2026-xx-yy
> Revision: 1
> News-Item-Format: 2.0
> Display-If-Installed: >=sys-kernel/dracut-111
>
> Dracut is an initramfs generation tool. It may be invoked via the
> installkernel mechanism or manually after building custom kernels.
>
> What changed?
> =============
>
> In version 111 of sys-kernel/dracut the default for the
> hostonly_cmdline setting changed from enabled to disabled.

[Blank line added here.]

> When enabled, this setting causes Dracut to attempt to detect which
> parameters are required on the kernel command line to boot the system.
> Examples are the root= parameter or parameters controlling partition
> decryption. These parameters are then included in the generated
> initramfs and appended to the kernel command line during boot.
>
> Why has this setting been changed?
> ==================================
>
> When enabled, Dracut's hostonly_cmdline setting may use the kernel
> command line of the running kernel (/proc/cmdline) to construct the
> kernel command line that will be embedded in the initramfs.

[Blank line added here.]

> This can cause problems when Dracut is being executed from a live or rescue
> environment. In such cases an incorrect root= could be included in the
> embedded kernel command line which could lead to boot failure.
>
> To prevent this behaviour from causing such unpleasant surprises, a
> check was added to sys-kernel/installkernel to detect whether the
> kernel was being installed from chroot and if Dracut was configured
> to include an embedded kernel command line (hostonly_cmdline=yes).

[Blank line added here.]

> While this check prevents boot failures, it also has the unfortunate
> side effect of creating a hard error that is triggered by default on
> new Gentoo installs. This has proven to be a significant stumbling
> block that new users often trip over. For this reason it was decided
> to disable the hostonly_cmdline setting in Gentoo's default settings
> for Dracut.
>
> User Action Required (all users)
> ================================
>
> When upgrading to Dracut version 111, a sanity check should be

"With >=dracut-111, users need to perform the sanity check this news
item describes.

This will ensure that kernel parameters ...

> performed to ensure that kernel parameters required to boot
> successfully are still present in the kernel command line. When in

This is okay to say, but tell me precisely what to run at least as well,
like:

"""
Suggested procedure for distribution kernels:
* Run emerge --config ... to regenerate the initramfs w/ dracut
* Get the cmdline in the just-made initramfs with: `...`
* Compare with /proc/cmdline
* If any important options are missing from the just-made initramfs, put
them in ...
"""

> doubt, ensure a system rescue media is close at hand. More specific

"ensure system rescue media" (no "a")

> instructions for various setups follow below, ordered from the
> specific to the more general.
>
> For each option a summarised list of relevant files that should be
> double checked is provided first. In general the 'lsinitrd' tool
> provided by sys-kernel/dracut can be used to obtain the current
> embedded kernel command line, these kernel parameters will be absent
> after (re)generating an initramfs with version 111 of dracut.
>
> As always, do not hesitate to use our support channels to ask for
> clarification or assistance.
>
> User Action Required (Systemd GPT Auto Generator)
> =================================================
> Files to double check:
> - /dev/gpt-auto-root (symlink must be valid)
>

Possibly: "If you don't have that, you are not using the auto generator."

> Systems that utilise the Systemd GPT Auto Generator mechanism to

s/Systemd/systemd/, and then on subsequent references, just "the auto
generator" IMO

> automatically detect and find the root partition at boot should not
> require any manual intervention. Though, before rebooting, users
> should verify that the GPT Auto Generator is actually being used and
> is working properly. To do so, check that /dev/gpt-auto-root currently
> exists and points to your root partition. For example:
>
> ls -l /dev/gpt-auto-root
>
> Should produce an output similar to the below if /dev/nvme0n1p1 is the
> root partition:
>
> lrwxrwxrwx 1 root root 4 May  2 10:33 /dev/gpt-auto-root -> nvme0n1p1
>
> If this is not the case then proceed with the instructions below that
> best match the setup to ensure that the root partition is set on the
> kernel command line using an alternative method.
>
> User Action Required (Generic Unified Kernel Image: "generic-uki")
> ==================================================================
> Files to double check:
> - none
>
> Users booting with the generic Unified Kernel Image (USE=generic-uki)
> functionality provided by the distribution kernels (dist-kernel) do
> not have to take any action as the hostonly_cmdline is already
> disabled in these builds:
> - sys-kernel/vanilla-kernel[generic-uki]
> - sys-kernel/gentoo-kernel[generic-uki]
> - sys-kernel/gentoo-kernel-bin[generic-uki]
>
> User Action Required (Unified Kernel Image with Secure Boot)
> ============================================================
> Files to double check:
> - /etc/kernel/cmdline and/or /etc/kernel/uki.conf (ukify)
> - /etc/dracut.conf and/or /etc/dracut.conf.d/*.conf (dracut)
>
> Booting a Unified Kernel Image (UKI) with Secure Boot enabled is a
> special case because in this situation the kernel command line
> supplied by the bootloader or the firmware is ignored and the built-in
> UKI command line, along with the parameters embedded in the initramfs,
> take precedence. The instructions below are also relevant if no
> kernel command line is set by the bootloader or the firmware.
>
> Verify whether Secure Boot is enabled with dmesg, for example:
>

  $ dmesg | grep -i secure
  ...

> dmesg | grep -i secure
> [    0.012418] Secure boot enabled
>
> An easy way to check the built-in kernel command line of an UKI is to
> use the lsinitrd tool provided by sys-kernel/dracut. For example:
>
> lsinitrd /efi/EFI/Linux/gentoo-x.y.z-gentoo-dist.efi
>
> This command will produce an output that could contain for example:
>
> <snip>
> Command line:
> quiet
> splash
> root=PARTUUID=7ae430c6-07e8-3b4e-a796-b2a28706b3fb
> <snip>

new line

> dracut cmdline:
> ro
>
> Showing that the built-in kernel command line for this UKI contains
> "quiet", "splash" and sets the root partition to the partition that
> has the partition UUID "7ae430c6-07e8-3b4e-a796-b2a28706b3fb".
> Additionally, the kernel command line embedded in the initramfs
> contains "ro".
>
> If kernel parameters that are essential for successfully booting
> the system (such as root=) are present in the "dracut cmdline"
> section but not in the "Command line" section then user intervention
> is required. In that case please adjust the configuration of the
> UKI generator to include the appropriate kernel parameters in the
> built-in UKI command line.
>
> If Ukify (sys-apps/systemd[ukify] or sys-apps/systemd-utils[ukify])
> is generating the UKI then adjust the "Cmdline=" setting in
> /etc/kernel/uki.conf. If that setting is not present in the uki.conf
> then adjust the kernel command line in /etc/kernel/cmdline.
>
> If Dracut itself is generating the UKI then please set or adjust the
> "kernel_cmdline=" setting in a dracut configuration file in
> /etc/dracut.conf.d/.
>
> If unsure which tool is generating the UKI then please inspect the
> current value of "uki_generator" in /usr/lib/kernel/install.conf and
> /etc/kernel/cmdline.
>
> User Action Required (GRUB)
> ===========================
> Files to double check:
> - /etc/default/grub
>
> Users booting with GRUB should compare the GRUB_CMDLINE_LINUX and
> GRUB_CMDLINE_LINUX_DEFAULT settings in /etc/default/grub against the
> kernel command line embedded in the initramfs or
> Unified Kernel Image (UKI). The lsinitrd utility provided by
> sys-kernel/dracut can be used for this purpose. For example, in the
> case of a plain initramfs:
>
> lsinitrd /boot/initramfs-x.y.z-gentoo-dist.img
>
> Or, in the case of an Unified Kernel Image:
> lsinitrd /boot/vmlinuz-x.y.z-gentoo-dist.efi
>
> The final lines of the output of these commands show which kernel
> parameters are embedded in the Dracut initramfs. For example:
>
> dracut cmdline:
> ro
>
> If kernel parameters that are essential for successfully booting
> the system (such as root=) are present in the "dracut cmdline"
> section but not in /etc/default/grub then user intervention is
> required. In that case please adjust the GRUB_CMDLINE_LINUX or
> GRUB_CMDLINE_LINUX_DEFAULT settings in /etc/default/grub to include
> the missing kernel parameters. After adjustments don't forget to
> update the grub.cfg. For example:
>
> grub-mkconfig -o /boot/grub/grub.cfg
>
> Note that when Secure Boot is enabled the grub.cfg might reside in a
> different directory, for example: /efi/EFI/Gentoo/grub.cfg.
>
> User Action Required (systemd-boot)
> ===================================
> Files to double check:
> - /etc/kernel/cmdline
>
> Users booting with systemd-boot should compare the contents of
> /etc/kernel/cmdline against the kernel command line embedded in the
> initramfs or Unified Kernel Image (UKI). If Unified Kernel Images are
> used and the /etc/kernel/cmdline file is empty or missing then no
> kernel command line is set by systemd-boot, in this case please refer
> to the "Unified Kernel Image with Secure Boot" section above, even if
> Secure Boot is not enabled.
>
> The lsinitrd utility provided by sys-kernel/dracut can be used to
> inspect the kernel parameters embedded in an initramfs or UKI. For
> example, in the case of a plain initramfs:
>
> lsinitrd /efi/gentoo/x.y.z-gentoo-dist/initrd
>
> Or, in the case of an Unified Kernel Image:
> lsinitrd /efi/EFI/Linux/gentoo-x.y.z-gentoo-dist.efi
>
> The final lines of the output of these commands show which kernel
> parameters are embedded in the Dracut initramfs. For example:
>
> dracut cmdline:
> ro
>
> If kernel parameters that are essential for successfully booting
> the system (such as root=) are present in the "dracut cmdline"
> section but not in /etc/kernel/cmdline then user intervention is
> required. In that case please adjust /etc/kernel/cmdline to include
> the missing kernel parameters.
>
> User Action Required (rEFInd)
> =============================
> Files to double check:
> - refind_linux.conf
>
> Users booting with rEFInd should compare kernel command line set
> in the refind_linux.conf file against the kernel command line embedded
> in the initramfs or Unified Kernel Image (UKI). The refind_linux.conf
> configuration file usually resides in /boot but may also be found
> elsewhere. If Unified Kernel Images are used and the refind_linux.conf
> configuration file is empty or missing then no kernel command line is
> set by rEFInd, in this case please refer to the "Unified Kernel Image
> with Secure Boot" section above, even if Secure Boot is not enabled.
>
> The lsinitrd utility provided by sys-kernel/dracut can be used to
> inspect the kernel parameters embedded in an initramfs or UKI. For
> example, in the case of a plain initramfs:
>
> lsinitrd /boot/initramfs-x.y.z-gentoo-dist.img
>
> Or, in the case of an Unified Kernel Image:
> lsinitrd /boot/vmlinuz-x.y.z-gentoo-dist.efi
>
> The final lines of the output of these commands show which kernel
> parameters are embedded in the Dracut initramfs. For example:
>
> dracut cmdline:
> ro
>
> If kernel parameters that are essential for successfully booting
> the system (such as root=) are present in the "dracut cmdline"
> section but not in the refind_linux.conf then user intervention is
> required. In that case please adjust refind_linux.conf to include the
> missing kernel parameters.
>
> User Action Required (other/general)
> ====================================
>
> For other setups please refer to the wiki page or manual of your
> bootloader and find where the kernel command line is set. Then
> compare this setting with the kernel parameters embedded in the
> initramfs. If essential parameters are present in the later but not in
> the former, then please move those parameters to your bootloader's
> configuration. When Unified Kernel Images are used then also consider
> the built-in UKI command line set by the UKI generator. Note that when
> Secure Boot is disabled, the bootloader may override the built-in UKI
> command line. However, when Secure Boot is enabled then any parameters
> set by the bootloader are ignored and the built-in UKI command line is
> always used.
>
> See Also
> ========
>
> [1] https://github.com/dracut-ng/dracut-ng/pull/2399
> [2] https://bugs.gentoo.org/971572

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[gentoo-dev] New News Item: 2026-xx-yy-dracut-hostonly-cmdline Nowa Ammerlaan <nowa@gentoo.org> - 2026-05-02 15:00 +0200
  Re: [gentoo-dev] New News Item v2: 2026-xx-yy-dracut-hostonly-cmdline Nowa Ammerlaan <nowa@gentoo.org> - 2026-05-07 13:00 +0200
    Re: [gentoo-dev] New News Item v2: 2026-xx-yy-dracut-hostonly-cmdline Sam James <sam@gentoo.org> - 2026-05-07 14:30 +0200

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