Wow, That was great piece of information.

Thanks a lot.

Regards,
Pattabhi Raman
dhoffman@cerner.com wrote:
> Unix wrote:
> > Hi Guru's
> >
> > I am facinga strange problem in AIX 5.3 (ML04), i have been fcing
> > issues with libraries.. Everything is working fine untill all of a
> > sudden, i start getting library loading error. i cannot execute any
> > command, every comman gives an output saying library cannot be loaded,
> > and no one can even telnet to the machine, when ever anyone tries to
> > telnet they get th emessage
> >
> > telnet (cagney)
> >
> > Could not load program login:
> > Dependent module libc.a(shr.o) could not be loaded.
> > Could not load module libc.a(shr.o).
>
> I was having the same problem. IBM AIX support informed me that there
> is a bug in the 64-bit kernel in AIX 5.3 ML4 which causes a memory
> leak. APAR IY84780 will address the issue; unfortunately, it is not
> available yet.
>
> http://www-1.ibm.com/support/docview...id=isg1IY84780
>
> IBM support has found that enabling MODS will normally prevent the
> problem from occurring until the APAR is available. The following is
> from a document that IBM sent to me.
>
> MODS (Memory Overlay Detection System)
>
>
> Overview
> Some of the most difficult types of problems to debug are what are
> generally called "memoryoverlays." Memory overlays include the
> following:
>
> · Writing to memory that is owned by another program or routine
> · Writing past the end (or before the beginning) of declared
> variables or arrays
> · Writing past the end (or before the beginning) of
> dynamically-allocated memory
> · Writing to or reading from freed memory
> · Freeing memory twice
> · Calling memory allocation routines with incorrect parameters or
> under incorrect conditions.
>
> In the kernel environment (including the AIX kernel, kernel extensions,
> and device drivers), memory overlay problems have been especially
> difficult to debug because tools for finding them have not been
> available.
>
> Starting with AIX Version 4.2.1, however, the Memory Overlay Detection
> System helps detect memory overlay problems in the AIX kernel, kernel
> extensions, and device drivers.
>
> How to Enable MODS
> # bosdebug -M
> # bosboot -a -d /dev/ipldevice
> # reboot the system
>
> How to Disaable MODS
> # bosdebug -o
> # bosboot -a -d /dev/ipldevice
> # reboot the system
>
> How to check the current status of MODS
> # bosdebug -L
> Memory debugger off <<<<< MODS is off
> Memory sizes 0
> Network memory sizes 0
> Kernel debugger off
> Real Time Kernel off
> Backtracking fault log off
>
> How MODS Works
> The primary goal of the MODS feature is to produce a dump file that
> accurately identifies the problem. MODS works by turning on additional
> checking to help detect the conditions listed above. When any of these
> conditions is detected, your system crashes immediately and produces a
> dump file that points directly at the offending code. (Previously, a
> system dump might point to unrelated code that happened to be running
> later when the invalid situation was finally detected.)
>
> Turning MODS on has a small impact on overall system performance and
> causes somewhat more memory to be used in the kernel and the network
> memory heaps. If your system is running at full CPU utilization or if
> you are already near the maximums for kernel memory usage, turning on
> the MODS may cause some performance degradation.