Hi All,

Now that i have applied the fix pack and updated my machine to ML5,
shoul i disable MODS??

Regards,
Pattabhi Raman
Unix wrote:
> 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.