Kdump over Ethernet or HFI for Linux diskless nodes

This document illustrates how to configure and use kdump on the RHEL6 and SLES11 diskless nodes.

• Overview
  • xCAT Interface
    • The pkglist file
  • Setup pkglist
    • The exclude file
    • The postinstall file
  • The dump attribute
  • The crashkernelsize attribute
  • The enablekdump postscript
  • The litefile table
  • Notes
  • How to trigger kernel panic on Linux
  • Dump Analysis

Overview

kdump is an advanced crash dumping mechanism. When enabled, the system is booted from the context of another kernel. This second kernel reserves a small amount of memory, and its only purpose is to capture the core dump image in case the system crashes. Since being able to analyze the core dump helps significantly to determine the exact cause of the system failure.

xCAT Interface

The pkglist, exclude and postinstall files location and name can be obtained by running the following command:

lsdef -t osimage <osimage name>

The pkglist file

For RHEL6 and RHEL7, there are two rpm packages for kdump:

     kexec-tools 
     crash

For SLES11, there are 3 rpm packages for kdump:

     kdump
     kexec-tools
     makedumpfile

For SLES10, there are 4 rpm packages for kdump:

    kernel-kdump
    kexec-tools
    kdump
    makedumpfile

Setup pkglist

Before setting up kdump,the approprite rpms should be added to the pkglist file as found by running:

lsdef -t osimage <osimage name>

The exclude file

The base diskless image excludes the /boot directory, but it is required for kdump. Update the exlist file and remove the entry for /boot. Then run the packimage or liteimg command to update your image with the changes.

The postinstall file

The kdump will create a new initrd which used in the dumping stage. The /tmp or /var/tmp directory will be used as the temporary directory. These 2 directory only are allocated 10M space by default. You need to enlarge it to 200M.

For RHELS6 or SLES10, modify the postinstall file to increase /tmp space:

 tmpfs   /var/tmp    tmpfs   defaults,size=200m   0 2

For SLES11, modify the postinstall file to increase /tmp/space.

 tmpfs   /tmp    tmpfs   defaults,size=200m       0 2

The dump attribute

In order to support kdump, the dump attribute was added into linuximage table, which is used to define the remote path where the crash information should be dumped to. Use the chdef command to change the image's dump attribute using the URI format.

  chdef -t osimage <image name> dump=nfs://<nfs_server_ip>/<kdump_path>

The <nfs_server_ip> can be excluded if the destination NFS server is the service or management node.

  chdef -t osimage <image name> dump=nfs:///<kdump_path>

The crashkernelsize attribute

For system x machine, on sles10 set the crashkernelsize attribute like this:

 chdef -t osimage <image name> crashkernelsize=<size>M@16M

On sles11 and rhels6 set the crashkernelsize attribute like this:

 chdef -t osimage <image name> crashkernelsize=<size>M

Where <size> recommended value is 256. For more information about the size can refer to the following information:

[https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/ch-kdump.html#s2-kdump-configuration-cli]
[http://www.novell.com/support/kb/doc.php?id=3374462]
[https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/s2-kdump-configuration-cli.html]
[http://www.novell.com/support/kb/doc.php?id=3374462]

For system p machine, set the crashkernelsize attribute to this:

  chdef -t osimage <image name> crashkernelsize=<size>@32M

Where <size> recommended value is 256, more information can refer the kdump document for the system x.

When your node starts, and you get a kdump start error like this:

  Your running kernel is using more than 70% of the amount of space you reserved for kdump,
   you should consider increasing your crashkernel

You should modify this attribute using this chdef command:

  chdef -t osimage <image name> crashkernelsize=512M@32M

If 512M@32M is not large enough, you should change the crashkernelsize larger like 1024M until the error message disappear.

The enablekdump postscript

This postscript enablekdump is used to start the kdump service when the node is booting up. Add it to your nodes list of postscripts by running this command:

  chdef -t node <node range> -p postscripts=enablekdump

The litefile table

This is for statelite images only. When the kdump service is starting, one special initial ramdisk for kdump will be generated if it does not exist. The initial ramdisk will be put into the /boot/ directory.

For RHEL6 statelite node:
YOu will need to add /boot/ to the litefile table. The config file (/etc/kdump.conf)
will be updated by the enablekdump postscript, so we also need to add /etc/kdump.conf to the litefile table. See below.

  tabdump litefile
  #image,file,options,comments,disable
  "ALL","/boot/",,,
  "ALL","/etc/kdump.conf",,,

For SLES11 statelite node

/lib/mkinitrd/ will be updated in the enablekdump postscript(the workaround for kdump on sles diskless install node). We need to add /lib/mkinitrd/ and /boot/ to the litefile table.

  tabdump litefile
  #image,file,options,comments,disable
  "ALL","/boot/",,,
  "ALL","/lib/mkinitrd/",,,

Notes

Currently, only NFS is supported for the setup of kdump.

If the dump attribute is not set, the kdump service will not be enabled.

Please make sure the NFS remote path(nfs://<nfs_server_ip>/<kdump_path>) is exported and it is read-writeable to the node where kdump service is enabled.

How to trigger kernel panic on Linux

Normally, kernel panic() will trigger booting into capture kernel. Once the kernel panic is triggered, the node will reboot into the capture kernel, and a kernel dump (vmcore) will be automatically saved to the directory on the specified NFS server (<nfs_server_ip>).

For RHESL6 the directory is <kdump_path>/var/crash/<node_ip>-<time>/ 

For SLES11 the directory is <kdump_path>/<node hostname>/<date>

For SLES10 the directory is <kdump_path>/<node hostname>

For RHELS6 testing purposes, you can simulate the trigger through /proc interface:

  echo c > /proc/sysrq-trigger

For SLES11.1 testing, you can use the following commands:

  echo 1 > /proc/sys/kernel/sysrq
  echo c > /proc/sysrq-trigger

This will force the Linux kernel to crash, and the address-YYYY-MM-DD-HH:MM:SS/vmcore file will be copied to the location you have selected on the specified NFS server directory.

Dump Analysis

Once the system has returned from recovering the crash, you may wish to analyze the kernel dump file using the crash tool.

1. Locate the recent vmcore dump file.

2. Locate the kernel file for the crash server(the kernel is under /tftpboot/xcat/netboot/<OS name="">/<ARCH>/<profile>/kernel on management node).

3. One you have located a vmcore dump file and kernel file, call crash

   crash <vmcore_dump_file> <kernel_file>

If crash cannot find any files under /usr/lib/debug? Make sure you have the kernel-debuginfo package installed.

For more information about the dump analysis you can refer the following documents:
[http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/s1-kdump-crash.html RHEL document]
[http://www.novell.com/support/kb/doc.php?id=3374462 SLES document]