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shmmax value

 
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Amit Manna_5
Advisor

shmmax value

I have a HP system OS version is 11.0 for
shmmax value is as follows:
kmtune -l -q shmmax
Parameter: shmmax
Value: 0XC0000000
Default: 0X4000000
Minimum: -
Module: -


Total VM : 1012mb Sys Mem : 244.7mb User Mem: 2.78gb Phys Mem: 4.00gb
Active VM: 257.9mb Buf Cache: 614.4mb Free Mem: 386.2mb

We are planning to upgrade the physical memory from 4 GB to 6 GB.

Do we need to increase the shmmax value and if yes to what value

What would be procedure for increasing it


many thanks in advance
21 REPLIES
Johnson Punniyalingam
Honored Contributor

Re: shmmax value

Hi Amit,

>>We are planning to upgrade the physical memory from 4 GB to 6 GB.<<

Your swap space should be double the size of your Pshyical RAM

if total Pshyical RAM 6GB you need have totol swap space of 12GB

# swapinfo -tam (Can check current size of you swap)

>>Do we need to increase the shmmax value and if yes to what value<<<

NO NEED

what Application are you running.?
do you have any perfromance issue?

Please below Thread for more Inforamtion

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1272448

Thanks,
Johnson


Problems are common to all, but attitude makes the difference
Mel Burslan
Honored Contributor
Solution

Re: shmmax value

>We are planning to upgrade the physical
>memory from 4 GB to 6 GB.
>
>Do we need to increase the shmmax value and
>if yes to what value

The answe is it depends, but more than likely it will be to your benefit to increase this value.

Most java-heavy applications running on hpux (and what is not java-heavy nowadays) wants you to set shmmax value to value which is equal to the amount of physical memory. Right now, you are saying you have 4GB physical memory on the system but your shmmax is set to 3GB. If it is configured like this for a reason, you need to figure out why it is that way and adjust the value according to the requirements of the person/vendor who wanted it that way. This will help you avoid headaches down the road.

If you are running Oracle, SAP, or any other java written application, in the lack of finding out what shmmax value needs to be, it is a safe bet to set it to the amount of physical memory, which will be 6GB in your case. SO the command to modify it should be as follows:

kmtune -s shmmax=6442450944

ans it is a dynamically configurable parameter, not needing a reboot.

Hope this helps
________________________________
UNIX because I majored in cryptology...
Tingli
Esteemed Contributor

Re: shmmax value

I think in oracle, the shmmax should be larger than the largest sga.
Emil Velez
Honored Contributor

Re: shmmax value

shmmax is the size of the largest shared memory segement that a program can create. A program can attach to multiple shared memory segments but this parameter is the largest size of a single shared memory segment.

Defer to your applications kernel parameter requirements.
Amit Manna_5
Advisor

Re: shmmax value

Does this parameter increase dont need reboot/
Ganesan R
Honored Contributor

Re: shmmax value

Hi Amit,

Changes to this tunable take effect immediately and does not need reboot.

Check this..

http://docs.hp.com/en/B2355-60127/shmmax.5.html

Best wishes,

Ganesh.
Steven E. Protter
Exalted Contributor

Re: shmmax value

Shalom,

Do you need to increase shmmax? No.

It might improve performance of applications like Oracle.

In this case I would do as follows:
sam
Kernel
Configurable parameters
Change shmmax

Compile kernel and boot via the menu.

Note: HP-UX 11.00 is out of support. I strongly urge a make_tape_recovery or make_net_recovery backup be done before any changes.

SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Sharma Sanjeev
Respected Contributor

Re: shmmax value

Hi Amit

Its not required to increase the value of shmmax after upgrade of memory but you can always increase it.

Its a Static value and requires reboot in 11.00

Regards
Sanjeev
Everything is Possible as " IMPOSSIBLE" word itself says I M POSSIBLE
Sharma Sanjeev
Respected Contributor

Re: shmmax value

Hi Amit

As you mentioned hp-ux version is 11.00 and in this version shmmax is static

shmmax 3221225472 3221225472 Static N/A

but not in 11.23

so it will require reboot after changing the value

Regards
Sanjeev
Everything is Possible as " IMPOSSIBLE" word itself says I M POSSIBLE
Shahul
Esteemed Contributor

Re: shmmax value


Hi,

Just for the reason of upgrading physical memory, you don't need to increase Shmmax. Check with you application vendor what should be you shmmax. When you upgrade your physical memory, the good prachtice is to alter your swap and dump. Again it is not a hard and fast rule, it's all depending on your requirement.

Good Luck
Shahul
Ganesan R
Honored Contributor

Re: shmmax value

Hi Amit,

I didn't noticed that your OS version is 11.0. I though it is higher version. In all higher versions, shmmax can be increased dynamically.
Best wishes,

Ganesh.
Amit Manna_5
Advisor

Re: shmmax value

hi
Can we increase the kernel paramter in single user mode. If yes please let me know the process.
Hein van den Heuvel
Honored Contributor

Re: shmmax value

>> Can we increase the kernel paramter in single user mode. If yes please let me know the process.

Noop.
That's why it is called 'kernel' param.
One setting for all.

Hein.
Sharma Sanjeev
Respected Contributor

Re: shmmax value

Hi Amit

You can not change/increase in Single User mode :-)

Regards
Sanjeev
Everything is Possible as " IMPOSSIBLE" word itself says I M POSSIBLE
Hein van den Heuvel
Honored Contributor

Re: shmmax value

oh wait, I guess I was reading the last question wrong (shouldn't visit forums before first coffee). I read it as 'for a single user', but surely it was 'with the system in single user mode'.
Yes, you can do that. But you can just set the parameters to chance (kctune) on the running system, for the next reboot.

Hein.
Avinash20
Honored Contributor

Re: shmmax value

On a running server

# kctune shmnax=

<< Above could be run without a reboot>

When you are ready with the downtime

# kmupdate
> Reboot the server

All the best
"Light travels faster than sound. That's why some people appear bright until you hear them speak."
Doug O'Leary
Honored Contributor

Re: shmmax value

Wow; what an entertainingly contradictory thread!

First, lets verify the environment:

It's an 11.00 system on which he's upgrading ram for 4 gigs to 6 gigs.


A couple of the more entertainingly incorrect answers:

1. kctune is 11.23 and 11.31; not 11.00. kmtune is the right command.

2. swap does not have to be 2x ram. That is archaic thinking - although, in this particular case, since it's an archaic operating system with an archaic amount of ram, the 2x ram may be right.

The right answer for the shmmax parameter is it doesn't have to be upgraded and you should check with the vendor. If you're running oracle, it probably should be. *That* being said, you're also probably running an antiquated version of oracle. Versions prior to 8.1.6 (I believe?) couldn't access more than 4 gigs of shared memory in one swell foop anyway, so updating the shmmax beyond that point doesn't get you much - and, may, in fact, prevent oracle from starting.

Should you decide to do the kernel upgrade, it will require a reboot. If you ever upgrade to 11.23 there are significantly more dynamic kernel parameters. Yet more in 11.31. Those two OSes make kernel updates a breeze, though. Run the appropriate kctune commands, then run kctune -D to find out if you need a reboot.

Here's a checklist for command line kernel creation that I always use:

http://www.olearycomputers.com/ll/hpkernel.html

This applies to 11.11 and prior; as I said, the 11.23/11.31 kernel process is so easy it doesn't require a checklist.

Hope that helps.

Doug O'Leary

------
Senior UNIX Admin
O'Leary Computers Inc
linkedin: http://www.linkedin.com/dkoleary
Resume: http://www.olearycomputers.com/resume.html
Avinash20
Honored Contributor

Re: shmmax value

"kctune in 11.11"

Oops.. Need good sleep before replying to number of thread.
Will make a habit of reading the complete thread bfor answering.

Thanks Doug for catching it ..
"Light travels faster than sound. That's why some people appear bright until you hear them speak."

Re: shmmax value

>Avinash: "kctune in 11.11" Need good sleep before replying to number of thread.

There is nothing wrong with mentioning kctune(1m) provided you put the right marketing spin on it. :-)
I.e. You can use kctune on 11.23 and shmmax is dynamic tunable so you don't have to reboot.
Amit Manna_5
Advisor

Re: shmmax value

while i am giving this

root@lust:>kmupdate
kmupdate: Newly built kernel /stand/build/vmunix_test is not found.


I am getting error as above. Please suggest what may be the issue
Avinash20
Honored Contributor

Re: shmmax value

Hi Amit,

1.) Procedure to generate a kernel at UX 11.00

1) Change to the kernel generation working directory and remove the files that have been left over from the last kernel generation:
# cd /stand/build
# rm -r * (Be careful with this! You need to be in /stand/build/)
2) Backup the current system file:
# cp /stand/system /stand/system.prev

7/33 Kernel Configuration Jan 2004
3) Is the system file up to date?
If you are not sure that the current system file (/stand/system) corresponds to the current kernel (/stand/vmunix), then use the system_prep script to extract a system file from the current kernel:
# /usr/lbin/sysadm/system_prep [-s /stand/system]
Compare the new system file to the original one. The diff command should not produce any results:
# diff /stand/system /stand/system.prev
4) Modify the system file
Use kmtune(1M) to modify kernel tunables. Use kmsystem(1M) to add/remove driver. These commands do nothing more than modifying /stand/system. Due to various dependencies, the system file should not be edited by hand. E.g.:
# kmtune -s shmmax= (changes tunable in system files)

5) Generate the kernel
After you modified the system file, you can generate the new kernel using the mk_kernel script. The name of the new kernel will be /stand/build/vmunix_test, unless explicitly specified through the -o option. The -s option specifies the system file to use, /stand/system is the default:
# mk_kernel
6) Schedule kernel update
kmupdate is used to initiate the move of the new kernel (/stand/build/vmunix_test) and the corresponding files to their appropriate places at the next shutdown or startup. The current kernel will be copied to /stand/vmunix.prev, then.
# kmupdate
7) Restart the system
The new kernel will be activated by restarting the system:
# cd /
# shutdown -ry now
"Light travels faster than sound. That's why some people appear bright until you hear them speak."