Linux sysctl Command with Practical Examples

Introduction

In this lab, you will learn how to use the sysctl command in Linux to view and modify kernel parameters at runtime. The sysctl command allows you to fine-tune the behavior of your Linux system by adjusting various kernel-level settings, such as networking, memory management, and security configurations. You will start by understanding the purpose and functionality of the sysctl command, then learn how to modify kernel parameters using the command, and finally, explore how to persist these configuration changes across system reboots.

Linux Commands Cheat Sheet

Skills Graph

Understand the Purpose and Functionality of sysctl Command

In this step, you will learn about the purpose and functionality of the sysctl command in Linux. The sysctl command is used to view and modify kernel parameters at runtime, allowing you to fine-tune the behavior of your Linux system.

The sysctl command allows you to:

• View the current value of a kernel parameter
• Modify the value of a kernel parameter
• Persist kernel parameter changes across system reboots

To view the current value of a kernel parameter, you can use the sysctl command with the parameter name:

$ sysctl kernel.hostname
kernel.hostname = ubuntu

This will display the current value of the kernel.hostname parameter.

To modify the value of a kernel parameter, you can use the -w or --write option:

$ sudo sysctl -w kernel.hostname=myhost
kernel.hostname = myhost

This will change the hostname of the system to myhost.

Example output:

$ sysctl kernel.hostname
kernel.hostname = myhost

The sysctl command provides access to a wide range of kernel parameters, allowing you to customize and optimize your Linux system for specific use cases.

Modify Kernel Parameters Using sysctl Command

In this step, you will learn how to use the sysctl command to modify kernel parameters in your Linux system.

The sysctl command allows you to view and change the values of various kernel parameters at runtime. This can be useful for tuning system performance, security, and other aspects of your Linux system.

To modify a kernel parameter using sysctl, you can use the -w or --write option followed by the parameter name and the new value:

$ sudo sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1

In this example, we're enabling IP forwarding by setting the net.ipv4.ip_forward parameter to 1.

You can also use the sysctl command to modify multiple parameters at once:

$ sudo sysctl -w net.ipv4.ip_forward=1 vm.swappiness=10
net.ipv4.ip_forward = 1
vm.swappiness = 10

Here, we're enabling IP forwarding and setting the vm.swappiness parameter to 10.

Example output:

$ sysctl net.ipv4.ip_forward vm.swappiness
net.ipv4.ip_forward = 1
vm.swappiness = 10

The changes made using the sysctl command are temporary and will be lost after a system reboot. To make the changes persistent, you'll need to modify the appropriate configuration file, which we'll cover in the next step.

Persist sysctl Configuration Changes Across Reboots

In the previous step, you learned how to use the sysctl command to modify kernel parameters. However, these changes are temporary and will be lost after a system reboot. In this step, you will learn how to make the sysctl configuration changes persistent across reboots.

To persist sysctl configuration changes, you need to modify the /etc/sysctl.conf file. This file is read by the kernel at boot time, and the specified kernel parameters are applied.

First, open the /etc/sysctl.conf file using a text editor:

$ sudo nano /etc/sysctl.conf

Then, add the kernel parameters you want to persist, one per line, in the following format:

parameter=value

For example, to persist the changes made in the previous step:

net.ipv4.ip_forward=1
vm.swappiness=10

Save the file and exit the text editor.

To apply the changes immediately, without waiting for a reboot, run the following command:

$ sudo sysctl -p

This will load the new configuration from the /etc/sysctl.conf file and apply the changes.

Example output:

$ sudo sysctl -p
net.ipv4.ip_forward = 1
vm.swappiness = 10

Now, the kernel parameter changes will persist across system reboots.

Summary

In this lab, you learned about the purpose and functionality of the sysctl command in Linux, which allows you to view and modify kernel parameters at runtime. You discovered how to use the sysctl command to view the current value of a kernel parameter, as well as how to modify the value of a parameter using the -w or --write option. Additionally, you learned that the sysctl command provides access to a wide range of kernel parameters, enabling you to customize and optimize your Linux system for specific use cases. Finally, you explored how to modify multiple kernel parameters simultaneously using the sysctl command.

Linux Commands Cheat Sheet