On Mon, Dec 28, 2020 at 4:48 PM Lianbo Jiang <lijiang(a)redhat.com> wrote:
Currently, the kdump sysconfig document is missed, let's add it to
the kexec-kdump-howto.txt as a document in order to help users better
understand these options in the /etc/sysconfig/kdump.
Signed-off-by: Lianbo Jiang <lijiang(a)redhat.com>
kexec-kdump-howto.txt | 85 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 80 insertions(+), 5 deletions(-)
diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt
index 447bc5447886..206bc1800486 100644
@@ -524,17 +524,92 @@ to send over the necessary ssh key file. Restart the kdump service
-Kdump boot directory
+About the /etc/sysconfig/kdump
+Currently, there are a few options in the /etc/sysconfig/kdump, which are
+usually used to control the behavior of kdump kernel. Basically, all of
+these options have default values, most time we do not need to change them,
+but sometimes, we may modify them in order to better control the behavior
+of kdump kernel such as debug, etc.
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.
Hi Lianbo, this line seems to be redundant?
+This represents the image type used for kdump. The default value is "vmlinuz"
+like KDUMP_IMG="vmlinuz". In general, do not change it.
I think this 'like KDUMP_IMG="vmlinuz"' sentence can be dropped. And
just ask user don't change it if they are not sure what this means.
+This represents the images extension. Relocatable kernels don't have one.
+Currently, it should be a null string, do not modify it.
Also, here, I think some sentence like "don't change it if you don't
know what it means" is better.
+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. Usually, no need to modify it.
I think the "no need to modify it" is not necessary, the doc describes
how this params works well.
+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'. Most time, no need to modify it.
+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
+all values from the '/proc/cmdline', which is not expected. As you know, some
+default kernel parameters could affect kdump, furthermore, that could cause
+the failure of kdump kernel boot.
+In addition, the option is also helpful when we want to make a debugging, we
make a debugging reads strange to me, maybe just say it's helpful to
debug the kdump kernel?
+can use this option to reconfigure kdump kernel command line.
+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.
+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.
+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