6:49 p.m.
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
-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)"
Estimate crashkernel
====================
--
2.31.1