IT Management

Linux on System z Kernel Dumps

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To trigger the dump under z/VM, a ZFCP adapter (device number 1700 in this example) must be specified for IPL with the dump (see Figure 5). The ZFCP dump tool writes the dump as a file into the specified file system. This file can be used directly for dump analysis; no zgetdump tool is needed.


VMDUMP: Under the z/VM hypervisor, the VMDUMP command can be used to create dumps for VM guests. To use VMDUMP, no preparation of any dump device is required; the dump file is written into virtual SPOOL. This dump mechanism should be used only for small guests because it’s quite slow. A Linux tool called vmur copies dump SPOOL files into Linux, and the vmconvert tool converts VMDUMPs into Linux-readable dump format (the --convert option on vmur can also convert the dump on the fly while receiving it from SPOOL). VMDUMP is the only non-disruptive dump method for Linux on System z and is also the only method to dump Named Saved Systems (NSSs).

Example of VMDUMP use:

  1. Trigger VMDUMP on the VM console: #cp vmdump.
  2. Boot Linux.
  3. Receive dump in Linux format from reader: vmur rec -c <dump spool id> dumpfile.

Automatic dump: When the Linux kernel crashes because of a non-recoverable error, normally, a kernel function named panic is called. By default, panic stops Linux. With Linux on System z, panic can be configured to automatically take a dump and re-IPL. The dump device is specified in the file /etc/sysconfig/dumpconf. Figure 6 shows the configuration for a DASD dump device. The service script dumpconf enables the configuration:

# service dumpconf start

and chkconfig can make the behavior persistent across reboot:

# chkconfig --add dumpconf

With this configuration, DASD device 0.0.4000 will be used for dump in case of a kernel crash. After the dump process finishes, the current system is rebooted. To instead stop the system after dumping, specify “ON_PANIC=dump” without the “reipl.”

How System z Dumps Compare to Kdump

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