How to configure kdump for a Red Hat Enterprise Linux system running on Microsoft Hyper-V

Solution Unverified - Updated

Environment

  • Red Hat Enterprise Linux 5, 6, or 7
  • Hyper-V host

Issue

  • Kdump service fails to start on RHEL system running on Hyper V
  • Kdump service starts, but crash kernel hangs while attempting to generate a core

Resolution

Note: It is necessary to manually reserve a specific memory amount for the crash kernel on the Grub kernel command line for Hyper-V systems. You cannot use the "crashkernel=auto" option

Note HyperV daemons are not available for RHEL 5. These instructions should work for RHEL 5 with LIS, but are provided by Microsoft and are not guaranteed to work in all situations

  • From here, please follow these steps. Note that these must be followed for any dump target (i.e. SSH, NFS, or local dump target).

RHEL 5 guests, on Hyper-V before 2012 R2

Ensure /etc/kdump.conf contains the following lines:

blacklist hv_vmbus hv_storvsc hv_utils hv_netvsc hid-hyperv
disk_timeout 100

Next, add the following options to the KDUMP_COMMANDLINE_APPEND line in /etc/sysconfig/kdump:

KDUMP_COMMANDLINE_APPEND="ide_core.prefer_ms_hyperv=0"

RHEL 6 guests, on Hyper-V before 2012 R2

Ensure /etc/kdump.conf contains the following lines:

extra_modules ata_piix sr_mod sd_mod
options ata_piix prefer_ms_hyperv=0
blacklist hv_vmbus hv_storvsc hv_utils hv_netvsc hid-hyperv
disk_timeout 100

Warning: There is a known issue which causes kdump to fail in RHEL6.7 and likely earlier versions when hosted on ws2012 r2. The fix for this issue was included in kernel version kernel-2.6.32-642.13.1.el6. This kernel is a 6.8 z-stream kernel.

RHEL 7 guests, on Hyper-V before 2012 R2

Ensure your /etc/kdump.conf file has the following options:

extra_modules ata_piix sr_mod sd_mod

Next, add the following options to the KDUMP_COMMANDLINE_APPEND line in /etc/sysconfig/kdump:

KDUMP_COMMANDLINE_APPEND="ata_piix.prefer_ms_hyperv=0 disk_timeout=100 rd.driver.blacklist=hv_vmbus,hv_storvsc,hv_utils,hv_netvsc,hid-hyperv"

RHEL 6 or 7 guests, on Hyper-V 2012 R2 and Hyper-V 2016 R2

On these systems, no /etc/kdump.conf modifications are required. Currently, October 2018, Windows Server 2012 R2 Hyper-V Generation 2 Virtual Machines are only certified with RHEL7. Windows Server 2016 Hyper-V Generation 2 Virtual Machines are certified with RHEL6 and RHEL7.

  • On RHEL6 with these newer Hyper-V, these BZs are relevant:
  • bz1333167 [Hyper-V][RHEL6.8] kdump triggered through NMI does not create vmcore dump file, fixed in RHEL6.9GA (and later), as well as for RHEL6.8.z in RHSA-2017-0036.
  • bz1301903 [Hyper-V][RHEL 6.8]Failure to get dump by "Sysrq" + "c" in RHEL on Hyper-V, fixed in RHEL6.9GA with RHSA-2017-0817

Root Cause

  • Hyper-V can not host two simultaneous connections from the same synthetic driver that's running inside a virtual machine. This means that kdump cannot utilize the Hyper-V storage driver, storvsc.

  • For this reason, these settings are intended to force the crash kernel to utilize standard Linux storage driver.

  • Hyper-V Generation 2 guests (supported since Hyper-V 2012 R2) have no longer IDE emulated disks available. On older Hyper-V guests, the paravirtualized drivers need to be blacklisted. On systems of the newer type, the paravirtualized drivers should be used.

Diagnostic Steps

  • Be aware that it can take some time for the kdump driver to fully initialize and write the core to disk.

  • The system may appear to hang with no console logs for a few minutes.

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