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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 :
crashkernel=384M-2G:64M,2G-:128M
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
USE_KDUMP: 1
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