Chapter 6. Configuring kernel parameters permanently by using the kernel_settings RHEL System Role

Procedure

1. Optionally, review the inventory file for illustration purposes:

   #  cat /home/jdoe/<ansible_project_name>/inventory
   [testingservers]
   pdoe@192.168.122.98
   fdoe@192.168.122.226
   
   [db-servers]
   db1.example.com
   db2.example.com
   
   [webservers]
   web1.example.com
   web2.example.com
   192.0.2.42

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   The file defines the [testingservers] group and other groups. It allows you to run Ansible more effectively against a specific set of systems.

2. Create a configuration file to set defaults and privilege escalation for Ansible operations.

   1. Create a new YAML file and open it in a text editor, for example:

      #  vi /home/jdoe/<ansible_project_name>/ansible.cfg

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   2. Insert the following content into the file:

      [defaults]
      inventory = ./inventory
      
      [privilege_escalation]
      become = true
      become_method = sudo
      become_user = root
      become_ask_pass = true

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      The [defaults] section specifies a path to the inventory file of managed hosts. The [privilege_escalation] section defines that user privileges be shifted to root on the specified managed hosts. This is necessary for successful configuration of kernel parameters. When Ansible playbook is run, you will be prompted for user password. The user automatically switches to root by means of sudo after connecting to a managed host.

3. Create an Ansible playbook that uses the kernel_settings role.

   1. Create a new YAML file and open it in a text editor, for example:

      #  vi /home/jdoe/<ansible_project_name>/kernel-roles.yml

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      This file represents a playbook and usually contains an ordered list of tasks, also called plays, that are run against specific managed hosts selected from your inventory file.

   2. Insert the following content into the file:

      ---
      -
        hosts: testingservers
        name: "Configure kernel settings"
        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

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      The name key is optional. It associates an arbitrary string with the play as a label and identifies what the play is for. The hosts key in the play 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.

      The vars section represents a list of variables containing selected kernel parameter names and values to which they have to be set.

      The roles key specifies what 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.

4. Optionally, verify that the syntax in your play is correct.

   #  ansible-playbook --syntax-check kernel-roles.yml
   
   playbook: kernel-roles.yml

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   This example shows the successful verification of a playbook.

5. Execute your playbook.

   #  ansible-playbook kernel-roles.yml
   
   ...
   
   BECOME password:
   
   PLAY [Configure kernel settings] **********************************************************************************
   
   
   
   PLAY RECAP ********************************************************************************************************
   fdoe@192.168.122.226       : ok=10   changed=4    unreachable=0    failed=0    skipped=6    rescued=0    ignored=0
   pdoe@192.168.122.98        : ok=10   changed=4    unreachable=0    failed=0    skipped=6    rescued=0    ignored=0

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   Before Ansible runs your playbook, you are going to be prompted for your password and so that a user on managed hosts can be switched to root, which is necessary for configuring kernel parameters.

   The recap section shows that the play finished successfully (failed=0) for all managed hosts, and that 4 kernel parameters have been applied (changed=4).

6. Restart your managed hosts and check the affected kernel parameters to verify that the changes have been applied and persist across reboots.