topic Re: Changing Kernel parameters shmmni and semmns? in Operating System - HP-UX

Changing Kernel parameters shmmni and semmns?

boje — Mon, 01 Sep 2008 11:00:51 GMT

Hi!

According to SAP note 172747 the kernel parameter shmmni should be >=512, our is set to 400. And the parameter semmns should be >=16384, our is set to 2520.
It is now time for me to add more memory to this server, and i was wondering if i should change these parameters? I am upgrading from 48GB to 96GB RAM.

Br
Patrik

Re: Changing Kernel parameters shmmni and semmns?

Dennis Handly — Mon, 01 Sep 2008 11:14:56 GMT

What OS version?
Might as well, you have to reboot.

Re: Changing Kernel parameters shmmni and semmns?

boje — Mon, 01 Sep 2008 11:17:32 GMT

OS is HP-UX 11.23

Yes i know i have to reboot.
I was more concerned about the values, what should it be set to? Is it going to cause any problem if i change these?

Br
Patrik

Re: Changing Kernel parameters shmmni and semmns?

Dennis Handly — Mon, 01 Sep 2008 11:38:02 GMT

>I was more concerned about the values, what should it be set to? Is it going to cause any problem if I change these?

I was thinking you should just follow SAP's advice.
You can read the manpages for details in kernel memory usage:
http://docs.hp.com/en/B2355-60130/shmmni.5.html
http://docs.hp.com/en/B2355-60130/semmns.5.html

You can also use kcusage(1m) to see the current usage values.

Re: Changing Kernel parameters shmmni and semmns?

TTr — Mon, 01 Sep 2008 11:49:36 GMT

You should set them to the recommended values. There is no impact on the server other that a minor increase in the kernel internal tables (a few kb). It is better to have extra than run out.
Since you are adding all that memory, you are expecting a lot of growth on your server. You have to be proactive and increase these and other parameters depending on the type of growth you are expecting. Parameter usage for these two and others is shown in glance, and "ipcs -a" and "sar -mv" commnads.

Re: Changing Kernel parameters shmmni and semmns?

boje — Mon, 01 Sep 2008 12:00:24 GMT

Thank you for your help! I will change to recommended values by SAP.
I will do some research before growth of this system. So weÂ´r not facing a bottleneck.

Br
Patrik

Re: Changing Kernel parameters shmmni and semmns?

Deepak Kr — Mon, 01 Sep 2008 12:10:09 GMT

Also, as you are going to add memory to server you may need to add some additional swap for further system tuning.

In older versions we also need to increase maxswapchunks when we add memory but here you dont need as you are using 11.23.

Take kernel and system file backup and go ahead!!

Re: Changing Kernel parameters shmmni and semmns?

boje — Mon, 01 Sep 2008 12:21:25 GMT

How to take kernel backup?

Br
Patrik

Re: Changing Kernel parameters shmmni and semmns?

Deepak Kr — Mon, 01 Sep 2008 13:27:53 GMT

HP-UX kernel resides under /stand FS

#ls -l /stand/vmunix

Take a backup using:

#cp -p /stand/vmunix /stand/vmunix.bak

# ls -ltr /stand/vmunix*

also backup system file using same method

Re: Changing Kernel parameters shmmni and semmns?

SKR_1 — Mon, 01 Sep 2008 14:46:27 GMT

when you will change the value through SAM, it automatically ask you to rebuild the kernal. So you need to take the copy of vmunix and system as well inside the /stand directory before changing the values.

Thanks

SKR

Re: Changing Kernel parameters shmmni and semmns?

boje — Tue, 02 Sep 2008 04:39:23 GMT

Hi!

I did copy vmunix and system. Changed parameters and shutdown system. Added memory and booted up again. All went well. Thank you for your support!

Br
Patrik

Re: Changing Kernel parameters shmmni and semmns?

Gokul Chandola — Tue, 02 Sep 2008 04:57:29 GMT

Dear Patrik,
Please take backup of /stand.
You can take copy of /stand/backup in another location this is privious kernal before reboot machine.
In case of your system is not booting then you can boot from ./stand/backup/vmunix.
If this will not work then you can use your backup path e.g ./BackupPath/backup/vmunix.

Regards,
Gokul Chandola

Re: Changing Kernel parameters shmmni and semmns?

Steven E. Protter — Tue, 02 Sep 2008 05:48:39 GMT

Shalom Patrik,

Prior to any kernel changes an Ignite make_tape_backup or make_net_backup to back up your previous boot image is a very good idea.

Glad your issue is resolved.

I tend to want to remove rules from the kernel configuration that are not mandatory. They were not developed by HP in a real world scenario and tend to make work for systems administrators that they don't need.

Thanks for using ITRC forums the best peer to peer help in the business.

:=)

SEP

Re: Changing Kernel parameters shmmni and semmns?

Deepak Kr — Tue, 02 Sep 2008 12:35:32 GMT

Boje,

adding detail to SEP's advice here. Please use following command to create ignite bootable tape on your hp-ux

#make_tape_recovery -I -v -x inc_entire=vg00

this will enable to rebuild your hp-ux in case something goes wrong with box in avoidable circumstances.

Cheers!!

deepak

Re: Changing Kernel parameters shmmni and semmns?

boje — Wed, 03 Sep 2008 05:46:28 GMT

Hi!

I have Ignite (make_net_recovery) running every Sunday on all my machines in the cluster. With the option entire vg00.

Br
Patrik

Re: Changing Kernel parameters shmmni and semmns?

boje — Wed, 03 Sep 2008 05:46:59 GMT

Solved