Chapter 6. Configuring kernel parameters permanently by using the kernel_settings RHEL system role

You can use the kernel_settings RHEL system role to configure kernel parameters on multiple clients at once. This solution:

  • Provides a friendly interface with efficient input setting.
  • Keeps all intended kernel parameters in one place.

After you run the kernel_settings role from the control machine, the kernel parameters are applied to the managed systems immediately and persist across reboots.

Important

Note that RHEL system role delivered over RHEL channels are available to RHEL customers as an RPM package in the default AppStream repository. RHEL system role are also available as a collection to customers with Ansible subscriptions over Ansible Automation Hub.

6.1. Introduction to the kernel_settings role

RHEL system roles is a set of roles that provide a consistent configuration interface to remotely manage multiple systems.

RHEL system roles were introduced for automated configurations of the kernel using the kernel_settings RHEL system role. The rhel-system-roles package contains this system role, and also the reference documentation.

To apply the kernel parameters on one or more systems in an automated fashion, use the kernel_settings role with one or more of its role variables of your choice in a playbook. A playbook is a list of one or more plays that are human-readable, and are written in the YAML format.

You can use an inventory file to define a set of systems that you want Ansible to configure according to the playbook.

With the kernel_settings role you can configure:

  • The kernel parameters using the kernel_settings_sysctl role variable
  • Various kernel subsystems, hardware devices, and device drivers using the kernel_settings_sysfs role variable
  • The CPU affinity for the systemd service manager and processes it forks using the kernel_settings_systemd_cpu_affinity role variable
  • The kernel memory subsystem transparent hugepages using the kernel_settings_transparent_hugepages and kernel_settings_transparent_hugepages_defrag role variables

Additional resources

6.2. Applying selected kernel parameters by using the kernel_settings role

Follow these steps to prepare and apply an Ansible playbook to remotely configure kernel parameters with persisting effect on multiple managed operating systems.

Prerequisites

Procedure

  1. Create a playbook file, for example ~/playbook.yml, with the following content: 

    ---
- name: Configure kernel settings
  hosts: managed-node-01.example.com
  roles:
    - rhel-system-roles.kernel_settings
  vars:
    kernel_settings_sysctl:
      - name: fs.file-max
        value: 400000
      - name: kernel.threads-max
        value: 65536
    kernel_settings_sysfs:
      - name: /sys/class/net/lo/mtu
        value: 65000
    kernel_settings_transparent_hugepages: madvise
    • name: optional key which associates an arbitrary string with the play as a label and identifies what the play is for.
    • hosts: key in the play which specifies the hosts against which the play is run. The value or values for this key can be provided as individual names of managed hosts or as groups of hosts as defined in the inventory file.
    • vars: section of the playbook which represents a list of variables containing selected kernel parameter names and values to which they have to be set.

    • role: key which specifies what RHEL system role is going to configure the parameters and values mentioned in the vars section.

      Note

      You can modify the kernel parameters and their values in the playbook to fit your needs.

  2. Validate the playbook syntax: 

    $ ansible-playbook --syntax-check ~/playbook.yml

    Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

  3. Run the playbook: 

    $ ansible-playbook ~/playbook.yml
  4. Restart your managed hosts and check the affected kernel parameters to verify that the changes have been applied and persist across reboots.

Additional resources