Need kernel tuning help with Red Hat Linux 7.0

[Debbie Fleith]

I'm installing a database application on our first Linux platform, and normally under other flavors of Unix, I need to adjust semaphore kernel parameters for the database.

Does Linux have a comparable command to "sysdef" which will display current kernel settings?

How would I change kernel settings under Linux?

[Vincent Stedema]

Hi,

Read the man page for sysctl. This is a program that can be used to set kernel parameters that are displayed under /proc/sys.

For instance, to get an overview of all tunable parameters:

# sysctl -A

Regards,

Vincent

[Kodjo Agbenu]

Hello Debbie,

Kernel parameters are available through /proc filesystem. Some of these kernels are dynamic. Of course, changing parameters on live systems may result in unexpected behaviour. That is why it is better to set them in system start scripts, before launching applications such as databases.

In /etc/rc.d/rc.sysinit, the sysctl program is called to set some dynamic parameters during system boot.

These parameters can be defined in file /etc/sysctl.conf. For example, to set the shmmax parameter, you should add something like this in /etc/sysctl.conf :

kernel.shmmax = value_in_bytes

It stands for :

echo "value_in_bytes" >/proc/sys/kernel/shmmax


Other remark : if you had the linux kernel source and documentation installed, you would find some useful information in /usr/src/linux/Documentation/sysctl.

Good luck.

Kodjo



P.S. Some database tuning requirements are related to buffer cache. Check /etc/fstab for mount options that disable the buffer cache (man mount -> "sync" option).