NixOS must take action when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage capacity.

If security personnel are not notified immediately when storage volume reaches 75 percent utilization, they are unable to plan for audit record storage capacity expansion.

Verify NixOS takes action when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage capacity with the following commands:

$ sudo grep -w space_left /etc/audit/auditd.conf

space_left = 25%

If the value of the "space_left" keyword is not set to "25%" or if the line is commented out, this is a finding.

Configure the operating system to initiate an action to notify the system administrator (SA) and information system security officer (ISSO) (at a minimum) when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage.

Add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix: environment.etc."audit/auditd.conf".text = [ '' space_left = 25% '' ];

Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch