Default variable details

Some of debops.sysctl default variables have more extensive configuration than simple strings or lists, here you can find documentation and examples for them.

sysctl__writable

Certain parts of the proc(5) filesystem can be mounted with read-only permissions to limit privileges in certain contexts, like unprivileged containers. Usually the /proc/sys/ filesystem is bind-mounted as read-only and specific paths inside which are correctly namespaced by the kernel, for example /proc/sys/net/ directory, are bind-mounted with read-write permissions.

When the sysctl command tries to modify kernel parameters in read-only path, it returns with an error. Since the debops.sysctl calls the sysctl command directly, in such case the playbook execution will stop and users will be forced to manually recover from the error.

To avoid this, the role checks via Ansible local facts, what paths in /proc/sys/ directory are writable, and only creates configuration entries for the paths that can be modified in the current context. Any parameters that cannot modify kernel variables will be automatically commented out with additional comment marking that parameter as read-only.

This mechanism is controlled by the sysctl__writable default variable. It contains a list of paths in the /proc/sys/ directory which can be written to, for example:

sysctl__writable: [ 'net', 'fs.nfs', 'kernel' ]

The path elements need to be separated by a dot (.) instead of a slash (/) to be correctly used by the role.

sysctl__parameters

The sysctl__*_parameters variables contain configuration of the kernel parameters stored in the /etc/sysctl.d/ directory. The variables are merged in the order specified by the sysctl__combined_parameters variable, the parameters can be manipulated using Ansible inventory without the need to copy the entire default variable.

Each list entry is a YAML dictionary that defines one configuration file with specific parameters:

name
Required. Name of the configuration section. Multiple entries with the same name will be merged together in order of appearance. The name is used as a part of the filename and it's best not to change it without complete redeployment of the configuration file.
filename

Optional. Specify the filename of the configuration file to manage in the /etc/sysctl.d/ directory (the .conf suffix needs to be included). If the filename parameter is not specified, the file will be named as:

/etc/sysctl.d/{{ weight }}-{{ name }}.conf
comment
Optional. A string or YAML text block with a comment added at the top of the generated configuration file.
state

Optional. Specify the desired state of the configuration file. Known states:

Value Description
present Default if not specified. The configuration file will be generated in the /etc/sysctl.d/ directory.
absent The configuration file will be removed from the /etc/sysctl.d/ directory if present, and it won't be generated.
comment The configuration file will be generated but all of the kernel parameters will be commented out. This can be used to disable the entire configuration file, preserving the set parameter values for reference.
ignore A given configuration entry will not be processed by the role and all of the kernel parameters defined in it will not be present in the generated configuration file.
options

Required. A list of entries that define kernel parameters present in a given configuration file. Each entry is a YAML dictionary, the entries can be specified in a simple or complex form. An example of a simple form:

sysctl__parameters:
  - name: 'network'
    options:

      - 'net.ipv4.ip_forward': True

      - 'net.ipv4.icmp_ratelimit': 100

Complex form is enabled when the name parameter is used. You can use the parameters:

name
Required. Name of the kernel parameter to configure.
value
Required. The value of a given kernel parameter which should be set. Values can be YAML booleans (converted to 0 or 1 in the configuration file), numbers and strings.
comment
Optional. String or YAML text block with additional comments about a given kernel parameter.
state

Optional. Specify the desired state of a given kernel parameter. Possible states:

Value Description
present The kernel parameter will be present in the generated configuration file.
absent The kernel parameter will be absent from the configuration file.
comment The kernel parameter will be present in the configuration file, but it will be commented out.
ignore A given option will be ignored by the role during template generation.

The options parameters from multiple configuration entries with the same name parameter are merged, you can use this to modify existing parameters defined in the role default variables via Ansible inventory, without copying the entire default variable.

Examples

Enable IPv4 forwarding using the default configuration:

sysctl__parameters:

  - name: 'network'
    options:

      - name: 'net.ipv4.ip_forward'
        Value: True

You can also check the sysctl__default_parameters variable for more examples.