When an unexpected system halt occurs, the system dump facility automatically copies selected areas of kernel data to the primary dump device. These areas include kernel segment 0 as well as other areas registered in the Master Dump Table by kernel modules or kernel extensions. An attempt is made to dump to the secondary dump device if it has been defined.
When you install the operating system, the dump device is automatically configured for you. By default, the primary device is /dev/hd6, which is a paging logical volume, and the secondary device is /dev/sysdumpnull.
If a dump occurs to paging space, the system will automatically copy the dump when the system is rebooted. By default, the dump is copied to a directory in the root volume group, /var/adm/ras. See the sysdumpdev command for details on how to control dump copying.
If you are using AIX 4.3.2 or later, compressing your system dumps before they are written to the dump device will reduce the size needed for dump devices. Refer to the sysdumpdev command for more details.
Starting with AIX 5.1, the dumpcheck facility will notify you if your dump device needs to be larger, or the file system containing the copy directory is too small. It will also automatically turn compression on if this will alleviate these conditions. This notification appears in the system error log. If you need to increase the size of your dump device, refer to the article in this publication, Increasing the Size of a Dump Device.
For maximum effectiveness, dumpcheck should be run when the system is most heavily loaded. At such times, the system dump is most likely to be at its maximum size. Also, even with dumpcheck watching the dump size, it may still happen that the dump won't fit on the dump device or in the copy directory at the time it happens. This could occur if there is a peak in system load right at dump time.
To have your device driver data areas included in a system dump, you must register the data areas in the master dump table. In AIX 5.1, use the dmp_ctl kernel service to add an entry to the master dump table or to delete an entry. The syntax is as follows:
#include <sys/types.h> #include <sys/errno.h> #include <sys/dump.h> int dmp_ctl(op, data) int op; struct dmpctl_data *data;
Before AIX 5.1, use the dmp_add kernel service. For more information, see dmp_add Kernel Service in AIX 5L Version 5.2 Technical Reference: Kernel and Subsystems Volume 1.