6:48 p.m.
On Wed, Dec 29, 2021 at 09:25:41PM +0800, Pingfan Liu wrote:
On Tue, Dec 28, 2021 at 08:49:30AM +0800, Coiby Xu wrote:
> Update crashkernel-howto since crashkernel.default has been removed. The
> documentation is also simplified as a result.
>
> Signed-off-by: Coiby Xu <coxu(a)redhat.com>
> ---
> crashkernel-howto.txt | 123 +++++++-----------------------------------
> 1 file changed, 19 insertions(+), 104 deletions(-)
>
> diff --git a/crashkernel-howto.txt b/crashkernel-howto.txt
> index 20f50e03..15768ab4 100644
> --- a/crashkernel-howto.txt
> +++ b/crashkernel-howto.txt
> @@ -13,13 +13,14 @@ kdump after you updated the `crashkernel=` value or changed the
dump target.
> Default crashkernel value
> =========================
>
> -Latest kernel packages include a `crashkernel.default` file installed in kernel
> -modules folder, available as:
> +Latest kexec-tools provides "kdumpctl get-default-crashkernel" to
retrieve
> +the default crashkernel value,
>
> - /usr/lib/modules/<kernel>/crashkernel.default
> + $ echo $(kdumpctl get-default-crashkernel)
> + 1G-4G:192M,4G-64G:256M,64G-102400T:512M
^^^ A
>
> -The content of the file will be taken as the default value of
'crashkernel=', or
> -take this file as a reference for setting crashkernel value manually.
> +It will be taken as the default value of 'crashkernel=', you can use
> +this value as a reference for setting crashkernel value manually.
>
>
> New installed system
> @@ -27,7 +28,7 @@ New installed system
>
> Anaconda is the OS installer which sets all the kernel boot cmdline on a newly
> installed system. If kdump is enabled during Anaconda installation, Anaconda
> -will use the `crashkernel.default` file as the default `crashkernel=` value on
> +will use the default crashkernel value as the default `crashkernel=` value on
> the newly installed system.
>
> Users can override the value during Anaconda installation manually.
> @@ -36,20 +37,11 @@ Users can override the value during Anaconda installation
manually.
> Auto update of crashkernel boot parameter
> =========================================
>
> -Following context in this section assumes all kernel packages have a
> -`crashkernel.default` file bundled, which is true for the latest official kernel
> -packages. For kexec-tools behavior with a kernel that doesn't have a
> -`crashkernel.default` file, please refer to the “Custom Kernel” section of this
> -doc.
> -
> -When `crashkernel=` is using the default value, kexec-tools will need to update
> -the `crashkernel=` value of new installed kernels, since the default value may
> -change in new kernel packages.
> -
> -kexec-tools does so by adding a kernel installation hook, which gets triggered
> -every time a new kernel is installed, so kexec-tools can do necessary checks and
> -updates.
> -
> +A new release of kexec-tools could update the the default crashkernel value.
> +By default, kexec-tools would reset crashkernel to the new default value if it
> +detects old default crashkernel value is used by installed kernels. If you
don't
> +want kexec-tools to update the old default crashkernel to the new default
> +crashkernel, you can change auto_reset_crashkernel to no in kdump.conf.
>
> Supported Bootloaders
> ---------------------
> @@ -59,92 +51,13 @@ on `grubby`. If other boot loaders are used, the user will have
to update the
> `crashkernel=` value manually.
>
>
> -Updating kernel package
> ------------------------
> -
> -When a new version of package kernel is released in the official repository, the
> -package will always come with a `crashkernel.default` file bundled. Kexec-tools
> -will act with following rules:
> -
> -If current boot kernel is using the default `crashkernel=` boot param value from
> -its `crashkernel.default` file, then kexec-tools will update new installed
> -kernel’s `crashkernel=` boot param using the value from the new installed
> -kernel’s `crashkernel.default` file. This ensures `crashkernel=` is always using
> -the latest default value.
> -
> -If current boot kernel's `crashkernel=` value is set to a non-default value,
the
> -new installed kernel simply inherits this value.
> -
> -On systems using GRUB2 as the bootloader, each kernel has its own boot entry,
> -making it possible to set different `crashkernel=` boot param values for
> -different kernels. So kexec-tools won’t touch any already installed kernel's
> -boot param, only new installed kernel's `crashkernel=` boot param value will be
> -updated.
> -
> -But some utilities like `grub2-mkconfig` and `grubby` can override all boot
> -entry's boot params with the boot params value from the GRUB config file
> -`/etc/defaults/grub`, so kexec-tools will also update the GRUB config file in
> -case old `crashkernel=` value overrides new installed kernel’s boot param.
> -
> -
> -Downgrading kernel package
> ---------------------------
> -
> -When upgrading a kernel package, kexec-tools may update the `crashkernel=` value
> -in GRUB2 config file to the new value. So when downgrading the kernel package,
> -kexec-tools will also try to revert that update by setting GRUB2 config file’s
> -`crashkernel=` value back to the default value in the older kernel package. This
> -will only occur when the GRUB2 config file is using the default `crashkernel=`
> -value.
> -
> -
> -Custom kernel
> -=============
> -
> -To make auto crashkernel update more robust, kexec-tools will try to keep
> -tracking the default 'crashkernel=` value with kernels that don’t have a
> -`crashkernel.default` file, such kernels are referred to as “custom kernel” in
> -this doc. This is only a best-effort support to make it easier debugging and
> -testing the system.
> -
> -When installing a custom kernel that doesn’t have a `crashkernel.default` file,
> -the `crashkernel=` value will be simply inherited from the current boot kernel.
> -
> -When installing a new official kernel package and current boot kernel is a
> -custom kernel, since the boot kernel doesn’t have a `crashkernel.default` file,
> -kexec-tools will iterate installed kernels and check if the boot kernel
> -inherited the default value from any other existing kernels’
> -`crashkernel.default` file. If a matching `crashkernel.default` file is found,
> -kexec-tools will update the new installed kernel `crashkernel=` boot param using
> -the value from the new installed kernel’s `crashkernel.default` file, ensures
> -the auto crashkernel value update won’t break over one or two custom kernel
> -installations.
> -
> -It is possible that the auto crashkernel value update will fail when custom
> -kernels are used. One example is a custom kernel inheriting the default
> -`crashkernel=` value from an older official kernel package, but later that
> -kernel package is uninstalled. So when booted with the custom kernel,
> -kexec-tools can't determine if the boot kernel is inheriting a default
> -`crashkernel=` value from any official build. In such a case, please refer to
> -the "Reset crashkernel to default value" section of this doc.
> -
> -
> Reset crashkernel to default value
> ==================================
>
> kexec-tools only perform the auto update of crashkernel value when it can
> confirm the boot kernel's crashkernel value is using its corresponding default
> -value or inherited from any installed kernel.
> -
> -kexec-tools may fail to determine if the boot kernel is using default
> -crashkernel value in some use cases:
> -- kexec-tools package is absent during a kernel package upgrade, and the new
> - kernel package’s `crashkernel.default` value has changed.
> -- Custom kernel is used and the kernel it inherits `crashkernel=` value from is
> - uninstalled.
> -
> -So it's recommended to reset the crashkernel value if users have uninstalled
> -kexec-tools or using a custom kernel.
> +value and auto_reset_crashkernel=yes in kdump.conf. In other cases, the user
> +can reset the crasherknel value by themselves.
>
> Reset using kdumpctl
> --------------------
> @@ -152,12 +65,14 @@ Reset using kdumpctl
> To make it easier to reset the `crashkernel=` kernel cmdline to this default
> value properly, `kdumpctl` also provides a sub-command:
>
> - `kdumpctl reset-crashkernel [<kernel version>]`
> + `kdumpctl reset-crashkernel [--kernel=path_to_kernel] [--reboot]`
>
> This command will read from the `crashkernel.default` file and reset
> bootloader's kernel cmdline to the default value. It will also update
bootloader
> config if the bootloader has a standalone config file. User will have to reboot
> -the machine after this command to make it take effect.
> +the machine after this command to make it take effect if --reboot is not specified.
> +For ppc64le, an optional "[--fadump=[on|off|nocma]]" can also be specified
to toggle
> +FADump on/off.
>
> Reset manually
> --------------
> @@ -166,7 +81,7 @@ To reset the crashkernel value manually, it's recommended to
use utils like
> `grubby`. A one liner script for resetting `crashkernel=` value of all installed
> kernels to current boot kernel's crashkernel.default` is:
>
> - grubby --update-kernel ALL --args "$(cat /usr/lib/modules/$(uname
-r)/crashkernel.default)"
> + grubby --update-kernel ALL --args "$(kdumpctl get-default-crashkernel)"
^^^ B
Either A or B should contain "crashkernel="
I should add "crashkernel=". Thanks for catching this mistake!
Else,
Reviewed-by: Pingfan Liu <piliu(a)redhat.com>
>
> Estimate crashkernel
> ====================
> --
> 2.31.1
>
--
Best regards,
Coiby