Linux - Kernel Parameter Management (sysctl.conf)

How to get and set the values of the Kernel Parameter

This article talks about the Kernel Parameters Management and show you how to change them.

How to

Get the value of a parameter?

Enter the following command to display the current values of the kernel parameters:

# /sbin/sysctl -a | grep para

where para is the beginning letters of the kernel parameter(s).

For instance to show the semaphore parameters:

# /sbin/sysctl -a | grep sem

Change the value of a parameter?

If the value of any kernel parameter is different from the minimum value you want, then perform the following:

fs.aio-max-nr = 1048576
fs.file-max = 6815744
kernel.shmall = 2097152
kernel.shmmax = 536870912
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 262144
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 1048586
net.ipv4.tcp_wmem = 262144 262144 262144
net.ipv4.tcp_rmem = 4194304 4194304 4194304
  • By specifying the values in the /etc/sysctl.conf file, they persist when you restart the system.
  • Include lines only for the kernel parameter values that you want to change.
  • If any of the current values are larger than the minimum value, then specify the larger value.
  • For the semaphore parameters (kernel.sem), you must specify all four values.
  • On SUSE Linux Enterprise Server systems, you must perform other command to ensure that the system reads it.
  • After updating the values of kernel parameters in the /etc/sysctl.conf file, either restart the computer, or run the following command to make the changes in the /etc/sysctl.conf file available in the active kernel memory:
# /sbin/sysctl -p

Review the output from this command to verify that the values are correct. If the values are incorrect, edit the /etc/sysctl.conf file, then enter this command again.

  • Enter the command below to confirm that the values are set correctly.
/sbin/sysctl -a 

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