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Full Discussion: What exactly does Kernel parameters do ?
Top Forums UNIX for Dummies Questions & Answers What exactly does Kernel parameters do ? Post 302822907 by John K on Tuesday 18th of June 2013 11:01:32 AM
Old 06-18-2013
What exactly does Kernel parameters do ?
Virtual Machine running on VMWare workstation 9.2
os : RHEL 5.8
RAM : 2.5GB
Swap : 2.6gb
CPU : 1 virtual CPU


Surprizingly I couldn't find much from googling on What exactly does Kernel parameters do ?

I was under the impression that kernel parameters just set the limits/maximum for a certain resources in the server.

To install Oracle RDBMS in my Linux VM, i set /etc/sysctl.conf as shown below . I found these settings from google.

Code:
$ cat /etc/sysctl.conf
# Kernel sysctl configuration file for Red Hat Linux
#
# For binary values, 0 is disabled, 1 is enabled.  See sysctl(8) and
# sysctl.conf(5) for more details.

# Controls IP packet forwarding
net.ipv4.ip_forward = 0


net.ipv4.conf.default.rp_filter = 1

# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0


kernel.sysrq = 0

kernel.core_uses_pid = 1

# Controls the use of TCP syncookies
net.ipv4.tcp_syncookies = 1

# Controls the maximum size of a message, in bytes
kernel.msgmnb = 65536

# Controls the default maxmimum size of a mesage queue
kernel.msgmax = 65536

# Controls the maximum shared segment size, in bytes
kernel.shmmax = 68719476736

# Controls the maximum number of shared memory segments, in pages
kernel.shmall = 4294967296

kernel.core_pattern = core.%e.%t

# Oracle Settings
net.ipv4.ip_local_port_range=9000 65500
net.ipv4.tcp_rmem = 4096 262144 26214400
net.ipv4.tcp_wmem = 4096 262144 26214400
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
net.ipv4.tcp_timestamps = 0
vm.pagecache=30
vm.swappiness=100
kernel.shmmni=4096
kernel.sem=268 32000 100 142
fs.file-max=6815744
fs.aio-max-nr=1048576
vm.nr_hugepages=32768
#vm.nr_hugepages=0
vm.drop_caches=0
net.core.rmem_default=262144
net.core.wmem_default=262144
net.core.rmem_max=4194304
net.core.wmem_max=1048576

I restarted the VM after after editing /etc/sysctl.conf like above. But the Linux VM was hanging at startup. It took around 1 hour for the VM to actually come up and it was very slow. So, i reverted /etc/sysctl.conf to the original file.

Why was the VM hanging at startup ?

Has it got anything to do with the kernel.shmmax value? But I am just setting a maximum possible value here. Right ?
 

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LEARN ABOUT OPENSOLARIS

cpc_access

cpc_access(3CPC)				    CPU Performance Counters Library Functions					  cpc_access(3CPC)

NAME

       cpc_access - test access CPU performance counters

SYNOPSIS

       cc [ flag... ] file... -lcpc [ library... ]
       #include <libcpc.h>

       int cpc_access(void);

DESCRIPTION

       Access  to  CPU	performance  counters  is  possible only on systems where the appropriate hardware exists and is correctly configured. The
       cpc_access() function must be used to determine if the hardware exists and is accessible on the platform before any of the interfaces  that
       use the counters are invoked.

       When  the hardware is available, access to the per-process counters is always allowed to the process itself, and allowed to other processes
       mediated using the existing security mechanisms of /proc.

RETURN VALUES

       Upon successful completion, cpc_access() returns 0.  Otherwise, it returns -1 and sets errno to indicate the error.

       By default, two common errno values are decoded and cause the library to  print	an  error  message  using  its	reporting  mechanism.  See
       cpc_seterrfn(3CPC) for a description of how this behavior can be modified.

ERRORS

       The cpc_access() function will fail if:

       EAGAIN	 Another process may be sampling system-wide CPU statistics.

       ENOSYS	 CPU  performance  counters are inaccessible on this machine. This error can occur when the machine supports CPU performance coun-
		 ters, but some software components are missing. Check to see that all	CPU  Performance  Counter  packages  have  been  correctly
		 installed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |ATTRIBUTE TYPE		     |ATTRIBUTE VALUE		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Obsolete			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cpc(3CPC), cpc_open(3CPC), cpc_seterrfn(3CPC), libcpc(3LIB), proc(4), attributes(5)

NOTES

       The cpc_access() function exists for binary compatibility only. Source containing this function will not compile. This function is obsolete
       and might be removed in a future release. Applications should use cpc_open(3CPC) instead.

SunOS 5.11							    28 Mar 2005 						  cpc_access(3CPC)
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