Rebuilding the kernel on AIX 4.1/4.2

Rebuilding the kernel on AIX 4.1/4.2

Post by mna.. » Fri, 05 Jan 2001 20:19:03



This is probably a stupid question from someone use to working with SCO
Openserver - Is is possible to rebuild the kernel with updated
paramters on AIX systems?

I have been told that AIX dynamically sets the kernel parameters while
it is running - is this true?

Is there a way of seeing what the current values of the kernel
parameters are?

Thanks
Martin

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Rebuilding the kernel on AIX 4.1/4.2

Post by Zoltan Soo » Fri, 05 Jan 2001 21:23:34



> This is probably a stupid question from someone use to working with
SCO
> Openserver - Is is possible to rebuild the kernel with updated
> paramters on AIX systems?

No, it is not. Reason number one is that you do not have the source...

Quote:> I have been told that AIX dynamically sets the kernel parameters while
> it is running - is this true?

Yes. Some parameters are dinamically configured, some can be set using
a command such as vmtune or schedtune.

Quote:> Is there a way of seeing what the current values of the kernel
> parameters are?

Most probably. The commands you need are in /usr/samples/kernel. If
they are not there, install the bos.adt.samples fileset.

--

-zoltan-

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Rebuilding the kernel on AIX 4.1/4.2

Post by Ellerman, Scott [RICH2:2I38:EXCH » Sat, 06 Jan 2001 02:27:15


[snip]

Quote:> > Is there a way of seeing what the current values of the kernel
> > parameters are?

> Most probably. The commands you need are in /usr/samples/kernel. If
> they are not there, install the bos.adt.samples fileset.

Some of the parameters you might be interested in changing (like max.
processes per user) can be seen with 'lsattr -El sys0'.  Those parameters
can be changed with 'chdev -l sys0 -a parm-name=new-value', or through
'smitty chgsys'.  The parameter name is the first field on each line of the
lsattr output.  The second field shows the current value.  The third field
shows a short description of the attribute.  You can usually disregard the
last field (True/False) on each line as it has no relation to the actual
value of the attribute.

For example, to set the maximum number of processes allowed per user to 128
(default is 40, I think), run:
    chdev -l sys0 -a maxuproc=128

For networking-related parameters, '/usr/sbin/no -a' will show you the list
and current values.  'no -o parm-name=new-value' will change it until the
next reboot; if you want to change it permanently you should also edit
/etc/rc.net and put the command in there.

This is valid for all AIX 4.x releases.

Regards,
Scott

 
 
 

Rebuilding the kernel on AIX 4.1/4.2

Post by Alex Robinso » Sat, 06 Jan 2001 03:09:40




> This is probably a stupid question from someone use to working with
SCO
> Openserver - Is is possible to rebuild the kernel with updated
> paramters on AIX systems?

> I have been told that AIX dynamically sets the kernel parameters while
> it is running - is this true?

> Is there a way of seeing what the current values of the kernel
> parameters are?

Martin,

Not a stupid question. Remember, "There are no stuid questions, just
stupid answers". What you have seen with SCO is what I believe is known
as a 'monolithic kernel'. AIX is an altogether different beast.

Anyway, for AIX the answer depends on what you consider kernel
parameters. Some kernel parameters for other Unixes do not apply with
AIX, shared memory kernel values for Solaris being a good example.
Solaris also sets the number of pseudo ptys via settings in the
/etc/system file, which requires a reboot to take effect. In AIX this is
done via SMIT or the command line, on-line.

Also, be aware that in AIX some of what may be considered kernel values
are set within the ODM that AIX uses. These ODM values are then used in
various methods depending on what sub-system they apply to. In these
cases setting the value involves setting the value in the ODM, again
either via SMIT or a command from the command line.

As for seeing what the kernel value is, as can be seen from the above,
seeing the value will depend on where it is. Sometimes looking at
the ODM may be the answer, other times SMIT or a command from the
command line will show the value.

Regards,
Alex

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Rebuilding the kernel on AIX 4.1/4.2

Post by Joe Moo » Sat, 06 Jan 2001 03:16:04




Quote:>He's not being stupid.  Other UNIX's really do provide
>object, source and header files for recompilation or relinking
>when you need to change the value of a limit variable or
>add a device driver to the kernel.  According to the lore
>I've been told, that's the *only* way you could ever change
>those things on ( list old UNIX system here ).

Those old UNIX systems include Solaris, SunOS, and HP/UX.

Current versions of those systems still require relinking the kernel to,
for example, set a network interface to force 100Mbps, or change the number
of processes that can be running simultaneously.

These changes also require a reboot on those systems, but don't on AIX.

--Joe
--
Lord, what fools these mortals be!

 
 
 

Rebuilding the kernel on AIX 4.1/4.2

Post by jthom.. » Sat, 06 Jan 2001 04:03:59


For a pretty good summary of all AIX parameters there is a tool called
snap which is available in a complete install of AIX.  Try "man snap"
to see if it's loaded...

running snap -a creates a full summary of your system
in /tmp/ibmsupt/xxxx.  About 8 megabytes of ascii files result that
contain almost every parameter in your system.

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Rebuilding the kernel on AIX 4.1/4.2

Post by Joe Moo » Sat, 06 Jan 2001 22:44:37





>> Current versions of those systems still require relinking the kernel to,
>> for example, set a network interface to force 100Mbps, or change the number
>> of processes that can be running simultaneously.

>> These changes also require a reboot on those systems, but don't on AIX.

>I don't buy what you're saying about Solaris.  You can change
>a setting in /etc/system and reboot.  If you don't want to
>reboot, you can use adb -k to change it yourself.  You
>can also use modload and modinfo (like AIX's *kex* commands)
>to load and unload drivers dynamically.

I was basing my Solaris comment on my conversation with a Solaris admin
here.  Apparently, for certain (supported) cards, in order to disable
autonegotiation you have to change a value in one of the kernel header
files.

Quote:>Does what you're saying apply to HP-UX 11.0 as well?  I
>thought 10.20 was the last release that was non-dynamic.

10.20 is the last release I have dealt with directly.

--Joe
--
Lord, what fools these mortals be!

 
 
 

Rebuilding the kernel on AIX 4.1/4.2

Post by Nicholas Drone » Sun, 07 Jan 2001 03:37:45






>>> Current versions of those systems still require relinking the kernel to,
>>> for example, set a network interface to force 100Mbps, or change the number
>>> of processes that can be running simultaneously.

>>> These changes also require a reboot on those systems, but don't on AIX.

>>I don't buy what you're saying about Solaris.  You can change
>>a setting in /etc/system and reboot.  If you don't want to
>>reboot, you can use adb -k to change it yourself.  You
>>can also use modload and modinfo (like AIX's *kex* commands)
>>to load and unload drivers dynamically.
> I was basing my Solaris comment on my conversation with a Solaris admin
> here.  Apparently, for certain (supported) cards, in order to disable
> autonegotiation you have to change a value in one of the kernel header
> files.

That's not at all true.  Solaris doesn't ship with source code.
What he meant was that he had to change a value in /etc/system,
which is the same as modifying a kernel variable.

Regards,

Nick Dronen

 
 
 

1. Default Kernel Tuning Changes - AIX 4.1 - 4.2 - 4.3 ???

We observed a substantial and unexpected performance difference between
certain specific applications running on an SP 135 Wide Node (595 equiv)
and the same application running on a Power3 Wide (43P-260) node. The
difference was tracked down to AIX 4.2 vs AIX 4.3 rather than the
hardware,
and relates to the default value for the kernel tuning parameter
"numclust", which controls VMM write-behind.  It appears that the
default in AIX 4.1 and AIX 4.3 was numclust=1, as documented, but that
AIX 4.2 slipped in numclust=0.   Has anyone else experienced or
investigated this?  I presume that numclust=0 implies that VMM
write-behind is disabled, although it is not documented as such.
Straight sequential I/O to a LVM striped SSA disk subsystem is
substantially faster with numclust=1, but certain types of reverse-skip
sequential are substantially slower.   I've opened a PMR with IBM but
while they are scratching their heads I thought I'd seek the collective
wisdom of this group...

Thanks...

--
=============================
      Scott S. Denham
Manager, Computer Technology
    Western Geophysical
      scott.denham

=============================

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