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rpaskudniak
February 4th, 2010, 06:52 AM
Greetings.
Bottom line first: Is there a GUI or otherwise friendly tool to modify the kernel parameters? One that will give help on a highlighted parameters?

Now as to my reason for this question:

In preparing for an Informix installation, I may need to change some kernel parameters. I could follow the advice of Gérard BIGOT from a couple of years ago at this URL (https://lists.ubuntu.com/archives/ubuntu-users/2008-January/134978.html). However, messing with the kernel this way, by directly editing /etc/sysctl.conf, is a bit scary. I have already backed up the current one and started editing according the Informix machine notes. However, I have commented out my new settings. [:Chicken]

The scariest aspect of this is that the notes recommend settings to kernel parameters that I do not find in /proc/sys/kernel. for example, it recomments setting SHMMIN to 1 but when I can /proc/sys.kernel/shmmin, there is no such file. (I did find shmmax.) Similarly for the very logical shmseg (max number of shared memory segments) - not found. I am afraid to add these into sysctl.conf if the equivalent pseudo-files don't exist.

Additional question: Where [on-line] do I find all kernel parameters documented? This is so that I am more certain of what I am doing instead of relying on my memory. For example, I don't recall the names of the parameters that control Kernel-Asynchronous I/O (KAIO) events. Such a doc would be most helpful here.

Thanks much.

tgalati4
February 4th, 2010, 07:03 AM
What are your performance goals? Perhaps the default settings will work. I have found that tweaking has unintended consequences. The default settings work for a lot of workloads.

efflandt
February 4th, 2010, 08:24 AM
If you did a fresh 9.10 install (or updated to grub2 after 9.04 to 9.10 update) you modify kernel parameters in /etc/default/grub. The DEFAULT is for regular boot and without DEFAULT is for recovery boot. In this case I temporarily disabled "quiet splash" while installing a new digital monitor (actually 1080p HDTV), until I had a chance to modify /etc/usplash.conf to proper resolution.

#GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX_DEFAULT=""
GRUB_CMDLINE_LINUX=""

After any modifications sudo update-grub to update grub.cfg.

rpaskudniak
February 8th, 2010, 07:54 AM
In response to tgalati4:
ON my dinosaur box, I have no great performance goals. My concern is merely that the kernel resources that Informix requires are available. For example, I have seen that the default semaphore resources exceed the basic requirements. But the shared memory and KAIO resources listed in the machine notes were not found in the pseudo-files fro the kernel parameters. Hence, I need to find a way to set them so that the Informix engine will find them. Hence, editing /etc/sysctl.conf is a logical starting point.

This is why I am looking for on-line documentation or some nice package to adjust the parameters graphically. (I think I'm gonna give up on that last item. :-k )

As to efflandt: Your comments left me scratching my head for a while, since I could not see the relevance of the grub to this discussion. However, a google search of ubuntu kernel parameters led me to the GRUB2 page (https://help.ubuntu.com/community/Grub2). Still no discussion of actual parameters but I begin to see relevance. But no direct help yet. And since I updated from 9.04 to 9.10, I am still using the legacy GRUB. Converting to GRUB2 is rather intimidating, especially since the illustrated examples [in that page] seem to ignore Windows. (It's mentioned as "other OS" but not with explicit instructions.)

Still, Google is our friend here. If I find what I'm looking for, I will post it.

Thanks.