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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 ULTRIX

sizer

sizer(8)						      System Manager's Manual							  sizer(8)

Name
       sizer - a program that sizes system hardware

Syntax
       /etc/sizer [ options ]

Description
       The program reports various items of information about a kernel file and the running system.  It is also used to create a system configura-
       tion file in the doconfig command.

Options
       -b   Create a boot command file for the current system disk.  The program creates the appropriate and command files in These files can then
	    be used to update the systems console media.  This only applies for VAX 8600, VAX 780, VAX 6200, and VAX 3400 cpus.  This also applies
	    for the VAX 750 and VAX 8200 only if the system disk is connected to an HSC.

       -c   Return the CPU type of the running cpu.

       -t timezone
	    Use timezone in the config file.

       -wt  Returns the workstation display type.

       -wu  Returns the workstation display units.

       -k image
	    Use the indicated kernel file instead of This is useful when the running system is not or you wish information about a system that	is
	    not running.

       -n filename
	    Creates  a	configuration  file.   The system must be running the kernel unless the option is used. The option creates a configuration
	    file in and also a file required for called

	    NOTE: The user should run to build a new kernel.

       -r   Return only the name of the root device and partition.

       -s   Return only the CPU subtype of the running cpu.  This only applies to VAX cpus. It returns following values for the following cpus:

	       Returned
	       Value	 CPU

	       11	 VAX8800
	       10	 VAX8700
		9	 VAX8550
		8	 VAX8500
		6	 VAX8300
		5	 VAX8200
		4	 VAXstation/MVAX 2000/3100
		3	 VAX60
		1	 MVAXII, VAX3x00, VAX62xx

       The value 0 is returned for all other cpu types.

Files
See Also
       config(8), doconfig(8)
       ULTRIX Advanced Installation Guide

																	  sizer(8)
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