On Mon, Mar 22, 2021 at 7:26 PM Lianbo Jiang <lijiang(a)redhat.com> wrote:
Because there are some duplicated contents, this will remove the
infrequently used options descriptions from the "kexec-kdump-howto.txt",
only add the "KDUMP_COMMANDLINE_REMOVE" and
Signed-off-by: Lianbo Jiang <lijiang(a)redhat.com>
kexec-kdump-howto.txt | 78 +++++++++++++++----------------------------
1 file changed, 27 insertions(+), 51 deletions(-)
diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt
index 88af6078ae6e..d23dd24b3fc7 100644
@@ -525,7 +525,7 @@ Advanced Setups
Currently, there are a few options in /etc/sysconfig/kdump, which are
usually used to control the behavior of kdump kernel. Basically, all of
@@ -533,51 +533,29 @@ these options have default values, usually we do not need to change
but sometimes, we may modify them in order to better control the behavior
of kdump kernel such as debug, etc.
+Usually option of kexec utility is used to inherit the kernel cmdline
+from the 1st kernel for kdump kernel. E.g specifying --command-line=
+"`cat /proc/cmdline`" or simply using '--reuse-cmdline'. Then only
+modify KDUMP_COMMANDLINE_APPEND and KDUMP_COMMANDLINE_REMOVE in the
+/etc/sysconfig/kdump to adjust the kernel cmdline of kdump as expected.
Hi Lianbo, I find this part of the document a bit confusing to me.
The "Usually option of kexec utility ..." doesn't sound right, maybe
just descript how this kexec-tools scripts works is good enough, and
no need to go through kexec binary details.
+For detailed description of each options, please refer to the file
+Kdump boot directory
Usually kdump kernel is the same as 1st kernel. So kdump will try to find
kdump kernel under /boot according to /proc/cmdline. E.g we execute below
command and get an output:
BOOT_IMAGE=/xxx/vmlinuz-3.yyy.zzz root=xxxx .....
+Then kdump kernel will be /boot/xxx/vmlinuz-3.yyy.zzz.
+However a variable KDUMP_BOOTDIR in /etc/sysconfig/kdump is provided to
+user if kdump kernel is put in a different directory.
-Then kdump kernel will be /boot/xxx/vmlinuz-3.yyy.zzz. However, this option
-is provided to user if kdump kernel is put in a different directory.
-This represents the image type used for kdump. The default value is
-This represents the images extension. Relocatable kernels don't have one.
-Currently, it is a null string by default.
-Any additional kexec arguments required. For example:
-In most situations, this should be left empty. But, sometimes we hope to get
-additional kexec loading debugging information, we can add the '-d' option
-for the debugging.
-This is a kernel version string for the kdump kernel. If the version is not
-specified, the init script will try to find a kdump kernel with the same
-version number as the running kernel.
-The value of 'KDUMP_COMMANDLINE' will be passed to kdump kernel as command
-line parameters, this will likely match the contents of the grub kernel line.
-In general, if a command line is not specified, which means that it is a null
-string such as KDUMP_COMMANDLINE="", the default will be taken automatically
-from the '/proc/cmdline'.
This option allows us to remove arguments from the current kdump command line.
If we don't specify any parameters for the KDUMP_COMMANDLINE, it will inherit
@@ -586,30 +564,28 @@ default kernel parameters could affect kdump, furthermore, that
the failure of kdump kernel boot.
In addition, the option is also helpful to debug the kdump kernel, we can use
-this option to change kdump kernel command line.
+this option to change kdump kernel command line. For example:
-For more kernel parameters, please refer to kernel document.
+KDUMP_COMMANDLINE_REMOVE="hugepages hugepagesz slub_debug quiet log_buf_len
+For more kernel parameters, please refer to kernel document:
This option allows us to append arguments to the current kdump command line
after processed by the KDUMP_COMMANDLINE_REMOVE. For kdump kernel, some
specific modules require to be disabled like the mce, cgroup, numa, hest_disable,
etc. Those modules may waste memory or kdump kernel doesn't need them,
-furthermore, there may affect kdump kernel boot.
+furthermore, there may affect kdump kernel boot. For example:
Just like above option, it can be used to disable or enable some kernel
modules so that we can exclude any errors for kdump kernel, this is very
meaningful for debugging.
--KDUMP_STDLOGLVL | KDUMP_SYSLOGLVL | KDUMP_KMSGLOGLVL
-These variables are used to control the kdump log level in the first kernel.
-In the second kernel, kdump will use the rd.kdumploglvl option to set the log
-level in the above KDUMP_COMMANDLINE_APPEND.
-Logging levels: no logging(0), error(1), warn(2), info(3), debug(4)
Kdump Post-Capture Executable
Other parts looks good.