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6.5. Verification

To confirm that the kernel dump mechanism is enabled, there are a few things to verify. First, confirm that the crashkernel boot parameter is present (note: The following line has been split into two to fit the format of this document:

cat /proc/cmdline

BOOT_IMAGE=/vmlinuz-3.2.0-17-server root=/dev/mapper/PreciseS-root ro crashkernel=384M-2G:64M,2G-:128M

The crashkernel parameter has the following syntax:

crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset] range=start-[end] 'start' is inclusive and 'end' is exclusive.

So for the crashkernel parameter found in /proc/cmdline we would have :


The above value means:

• if the RAM is smaller than 384M, then don't reserve anything (this is the "rescue" case)

• if the RAM size is between 386M and 2G (exclusive), then reserve 64M

• if the RAM size is larger than 2G, then reserve 128M

Second, verify that the kernel has reserved the requested memory area for the kdump kernel by doing:

dmesg | grep -i crash


[ 0.000000] Reserving 64MB of memory at 800MB for crashkernel (System RAM: 1023MB)

Finally, as seen previously, the kdump-config show command displays the current status of the kdump-tools configuration :

kdump-config show

DUMP_MODE: kdump


KDUMP_SYSCTL: kernel.panic_on_oops=1 KDUMP_COREDIR: /var/crash

crashkernel addr: 0x2c000000

/var/lib/kdump/vmlinuz: symbolic link to /boot/vmlinuz-4.4.0-10-generic kdump initrd:

/var/lib/kdump/initrd.img: symbolic link to /var/lib/kdump/initrd.img-4.4.0-10-generic current state: ready to kdump

kexec command:

/sbin/kexec -p --command-line="BOOT_IMAGE=/vmlinuz-4.4.0-10-generic root=/dev/ mapper/VividS--vg-root ro debug break=init console=ttyS0,115200 irqpoll maxcpus=1 nousb

systemd.unit=kdump-tools.service" --initrd=/var/lib/kdump/initrd.img /var/lib/kdump/vmlinuz

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