Prerequisites
Kdump stores kernel core dumps under /var. The partition that /var is on must have enough available disk space for the vmcore file, which will be approximately the size of the system's physical memory. By default, the system will attempt to keep 5 vmcore files.
Check the taint status of the kernel (recommended)
Whenever possible, kernel crashes should be reproduced using untainted kernels.
Set up magic SysRq (recommended)
For kernel problems other than a kernel oops or panic, a kernel core dump is not triggered automatically. If the system still responds to keyboard input to some degree, a kernel core dump can be triggered manually through a "magic SysRq" keyboard combination (typically: hold down three keys simultaneously: the left Alt key, the Print Screen / SysRq key and a letter key indicating the command - ' s' for sync, ' c' for core dump), if this feature has been enabled.
For general documentation of the "magic SysRq" feature, please refer to the Documentation/sysrq.txt file in the Linux kernel source.
To enable the magic SysRq feature permanently, edit /etc/sysconfig/sysctl, change the ENABLE_SYSRQ line to ENABLE_SYSRQ="yes". This change becomes active after a reboot. To enable the feature for the running kernel, run
echo 1>/proc/sys/kernel/sysrq
Configure the system for capturing kernel core dumps (SLES 10)
- Install the packages kernel-kdump, kdump, and kexec-tools.
The kernel-kdump package contains a "crash" or "capture" kernel that is started when the primary kernel has crashed and which provides an environment in which the primary kernel's state can be captured. The version of the kernel-dump package needs to be identical to that of the kernel whose state needs to be captured.
The kexec-tools package contains the tools that make it possible to start the capture kernel from the primary kernel.
- Reserve memory for the capture kernel by passing appropriate parameters to the primary kernel.
For the x86 and x86_64 architecture use the table below based upon how much memory you have.
| Memory | crashkernel= |
| 0 - 12 GB | 64M@16M |
| 13 - 48 GB | 128M@16M |
| 49 - 128 GB | 256M@16M |
| 129 - 256 GB | 512M@16M |
For the PPC64 architecture: crashkernel=128M@32M
Note: for Xen installations, this parameter needs to be passed to the GRUB line for the Xen hypervisor, not the module line for the Dom0 kernel.
This can be done as follows: Start YaST, under System, select Boot Loader. On the tab Section Management, select the default section and select Edit. Add the settings to the field labeled Optional Kernel Command Line Parameter , then select Ok and Finish to save the settings.
- Activate the kdump system service.
Run
chkconfig kdump on
or in YaST: under System, select System Services (Runlevel), select kdump , then select Enable and Finish.
- Reboot the system for the settings to take effect
Test local kernel core dump capture
To test the local kernel core dump capture, follow these steps.
If magic SysRq has been configured:
- Magic-SysRq-S to sync (flush out pending writes)
- Magic-SysRq-C to trigger the kernel core dump
Alternatively, without magic SysRq:
- Open a shell or terminal
- Run sync
- Run echo c >/proc/sysrq-trigger
Please note that the 'c' must be lower case! Also, the system will not be responsive while the capture is being prepared and made as the capture kernel environment is a limited, non-interactive environment.
Once the system becomes responsive again, verify that a capture file was created as /var/log/dump/ date-time /vmcore.