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

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

On Thu, Mar 28, 2019 at 9:24 AM Gianluca Cecchi <gianluca.cecchi at
gmail.com>
wrote:
>
>
> 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
>
> [snip]
>
> 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"
>
>
The command line fo CentOS 6 clearly misses the kernel version to build
initrd file for, so the correct command should be:

/sbin/mkdumprd -d -f
"/boot/initrd-2.6.32-642.13.1.el6.x86_64kdump.img" 
2.6.32-642.13.1.el6.x86_64

On a test system of mine with version 6.8:
# /sbin/mkdumprd -d -f
"/boot/initrd-2.6.32-642.13.1.el6.x86_64kdump.img"
2.6.32-642.13.1.el6.x86_64
Warning: There might not be enough space to save a vmcore.
         The size of UUID=359ce627-f3b1-49a3-a9b9-f607435a40d9 should be
greater than 132250104 kilo bytes.
#

# ll /boot/initrd-2.6.32-642.13.1.el6.x86_64kdump.img
-rw------- 1 root root 7515358 Mar 28 09:52
/boot/initrd-2.6.32-642.13.1.el6.x86_64kdump.img

> -----Original Messages-----
> From: "Gianluca Cecchi" <gianluca.cecchi at gmail.com>
> Sent Time: 2019-03-28 16:59:19 (Thursday)
> [...]
> The command line fo CentOS 6 clearly misses the kernel version to build
> initrd file for, so the correct command should be:
> 
> /sbin/mkdumprd -d -f
> "/boot/initrd-2.6.32-642.13.1.el6.x86_64kdump.img" 
2.6.32-642.13.1.el6.x86_64
> 
I test it and it works for me, although prints some harmless warnings.

Thanks