CentOS - Mar 2019 - How to specify kernel version when restart kdump

What do you mean? Wouldn't the kernel version always be the actual 
running version of the kernel that was booted?

Ben

On 3/26/19 6:16 PM, wuzhouhui wrote:
>> -----Original Messages-----
>> From: "Benjamin Hauger" <hauger at noao.edu>
>> Sent Time: 2019-03-27 00:15:21 (Wednesday)
>> To: centos at centos.org
>> Cc:
>> Subject: Re: [CentOS] How to specify kernel version when restart kdump
>>
>> kdump operates by booting a fresh kernel to capture the context of a
>> crashed kernel, and so the only way for kdump to dump a kernel is to
>> crash it and cause kdump to invoke its post-crash kernel.
>>
>> You can manually force a running kernel to panic (and invoke a
>> correctly-configured kdump) with the following command sequence:
>>
>>>      echo 1 > /proc/sys/kernel/sysrq
>>>      echo c > /proc/sysrq-trigger
>>
>> Cheers,
>> Ben
> Hi, Ben
> 
> I think your response doesn't answered my question. I'm not asking
> how to trigger kernel crash and see whether the kdump is works, but
> asking how to specifying kernel version when start kdump service.
> 
> Thanks.
>>
>>
>> On 3/25/19 7:19 PM, wuzhouhui wrote:
>> CentOS at centos.org
>> https://lists.centos.org/mailman/listinfo/centos
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> https://lists.centos.org/mailman/listinfo/centos
> 
-- 

Benjamin Hauger
SysAdmin/CSDC-DMO
Rm. 94
x8371

> -----Original Messages-----
> From: "Benjamin Hauger" <hauger at noao.edu>
> Sent Time: 2019-03-28 01:31:40 (Thursday)
> To: wuzhouhui <wuzhouhui14 at mails.ucas.ac.cn>, centos at centos.org
> Cc: 
> Subject: Re: [CentOS] How to specify kernel version when restart kdump
> 
> What do you mean? Wouldn't the kernel version always be the actual 
> running version of the kernel that was booted?
> 
Suppose the running kernel is 2.6.32, and then I installed kernel 3.10.0.
The files under /boot includes (exclude some unimportant files):
  initramfs-2.6.32.img
  initramfs-3.10.0.img
  vmlinuz-2.6.32
  vmlinuz-3.10.0
  initrd-2.6.32kdump.img
We can see that there is no initrd-3.10.0kdump.img for newly installed
kernel 3.10.0, and kdump will generate initrd-3.10.0kdump.img only when
booted as kernel 3.10.0. However, I want kdump to generate
initrd-3.10.0kdump.img
now (the current running kernel is 2.6.32).
> Ben
> 
> On 3/26/19 6:16 PM, wuzhouhui wrote:
> >> -----Original Messages-----
> >> From: "Benjamin Hauger" <hauger at noao.edu>
> >> Sent Time: 2019-03-27 00:15:21 (Wednesday)
> >> To: centos at centos.org
> >> Cc:
> >> Subject: Re: [CentOS] How to specify kernel version when restart
kdump
> >>
> >> kdump operates by booting a fresh kernel to capture the context of
a
> >> crashed kernel, and so the only way for kdump to dump a kernel is
to
> >> crash it and cause kdump to invoke its post-crash kernel.
> >>
> >> You can manually force a running kernel to panic (and invoke a
> >> correctly-configured kdump) with the following command sequence:
> >>
> >>>      echo 1 > /proc/sys/kernel/sysrq
> >>>      echo c > /proc/sysrq-trigger
> >>
> >> Cheers,
> >> Ben
> > Hi, Ben
> > 
> > I think your response doesn't answered my question. I'm not
asking
> > how to trigger kernel crash and see whether the kdump is works, but
> > asking how to specifying kernel version when start kdump service.
> > 
> > Thanks.
> >>
> >>
> >> On 3/25/19 7:19 PM, wuzhouhui wrote:
> >> CentOS at centos.org
> >> https://lists.centos.org/mailman/listinfo/centos
> > _______________________________________________
> > CentOS mailing list
> > CentOS at centos.org
> > https://lists.centos.org/mailman/listinfo/centos
> > 
> 
> -- 
> 
> Benjamin Hauger
> SysAdmin/CSDC-DMO
> Rm. 94
> x8371

On Thu, Mar 28, 2019 at 6:55 AM wuzhouhui <wuzhouhui14 at
mails.ucas.ac.cn>
wrote:
> > -----Original Messages-----
> > From: "Benjamin Hauger" <hauger at noao.edu>
> > Sent Time: 2019-03-28 01:31:40 (Thursday)
> > To: wuzhouhui <wuzhouhui14 at mails.ucas.ac.cn>, centos at
centos.org
> > Cc:
> > Subject: Re: [CentOS] How to specify kernel version when restart kdump
> >
> > What do you mean? Wouldn't the kernel version always be the actual
> > running version of the kernel that was booted?
> >
> Suppose the running kernel is 2.6.32, and then I installed kernel 3.10.0.
> The files under /boot includes (exclude some unimportant files):
>   initramfs-2.6.32.img
>   initramfs-3.10.0.img
>   vmlinuz-2.6.32
>   vmlinuz-3.10.0
>   initrd-2.6.32kdump.img
> We can see that there is no initrd-3.10.0kdump.img for newly installed
> kernel 3.10.0, and kdump will generate initrd-3.10.0kdump.img only when
> booted as kernel 3.10.0. However, I want kdump to generate
> initrd-3.10.0kdump.img
> now (the current running kernel is 2.6.32).
>
>
Your particolar versions seem quite strange because 2.6.32 lets me think
about CentOS 6 and 3.10.0 lets me think about CentOS 7.
Any way see below for some discussion, not tried by me, so in case please
use on test system before.

1) In CentOS 6 we have the classical SysV service
file: /etc/rc.d/init.d/kdump

Supposing you have just installed 2.6.32-642.13.1.el6.x86_64 kernel

Analyzing what it runs we have

DUMP_KERNELVER=""
MKDUMPRD_ARGS=""

. /etc/sysconfig/kdump
In my case:
KDUMP_BOOTDIR="/boot"

local running_kernel=`uname -r`
kdump_kver=`echo $running_kernel | sed 's/smp//g'`
MKDUMPRD="/sbin/mkdumprd -d -f $MKDUMPRD_ARGS"

kdump_initrd="${KDUMP_BOOTDIR}/initrd-${kdump_kver}kdump.img"

and at the end it runs this command if it doesn't find one:
$MKDUMPRD $kdump_initrd $kdump_kver

that tipically will translate in:

/sbin/mkdumprd -d -f
"/boot/initrd-2.6.32-642.13.1.el6.x86_64kdump.img"


2) In CentOS 7 we have systemd unit files and for
kdump: /usr/lib/systemd/system/kdump.service

Supposing you have just installed 3.10.0-693.21.1.el7.x86_64

The script called actually it is /usr/bin/kdumpctl

See also fadump (firmware assisted dump) concepts in RHEL 7 / CentOS 7:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/kernel_administration_guide/kernel_crash_dump_guide

But I think you are x86_64 so kdump sttill applies
In kdumpctl we have something like this:

MKDUMPRD="/sbin/mkdumprd -f"
TARGET_INITRD=""

. /lib/kdump/kdump-lib.sh

. /etc/sysconfig/kdump

eval $(cat /proc/cmdline| grep "BOOT_IMAGE" | cut -d' ' -f1)
KDUMP_BOOTDIR="/boot"$(dirname $BOOT_IMAGE)

kdump_kver=`uname -r`
TARGET_INITRD="${KDUMP_BOOTDIR}/initramfs-${kdump_kver}kdump.img"

rebuild_kdump_initrd()
{
        $MKDUMPRD $TARGET_INITRD $kdump_kver
        if [ $? != 0 ]; then
                echo "mkdumprd: failed to make kdump initrd"
>&2
                return 1
        fi

        return 0
}

So at the end the command will be:

$MKDUMPRD $TARGET_INITRD $kdump_kver

that in general should be something like this if you want to compile for
kernel 3.10.0-693.21.1.el7.x86_64 :

/sbin/mkdumprd -f /boot/initramfs-3.10.0-693.21.1.el7.x86_64kdump.img
3.10.0-693.21.1.el7.x86_64

HIH trying,
Gianluca