Anyone ever experienced a core dump when running NMON. I am running AIX 5.3 on an 8 CPU LPAR (P570). This has only recently started to happen.

Not personally but:
http://www-128.ibm.com/developerwork...u-analyze_aix/
"Even though IBM doesn't officially support the tool and you must use it at your own risk"
"Usage notes: This nmon tool is NOT OFFICIALLY SUPPORTED. No warrantee is given or implied, and you cannot obtain help with it from IBM."
Any performance tool can case problems. They all add extra load to the cpu and memory, and if the system was in trouble before you started using them they wll often push the system over the edge.
Try using the AIX tools to see if you can work out the problem without nmon.
topas, iostat, vmstat, etc.

I realise this is not a supported tool, the whole reason why I posted a message here. If it was supported I would have reported it ti Call AIX by now.

Solved. This LPAR had been setup wrongly. It has 8 physical CPUs and had been set to 24 logical (48 when lparstat is run). This was effecting the shared memory paging. When I ran nmon as a normal user (not root) the first thing it looked was /dev/kmem (kernel shared memory). When I changed the permissions on the device so world had rights to it the core dump occurred. I have now reduced the logical CPUs down to match the physical and nmon is now working again. Strange.