NixOS must notify the system administrator (SA) and information system security officer (ISSO) (at a minimum) when allocated audit record storage volume reaches 75 percent utilization.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-268101	SRG-OS-000046-GPOS-00022	ANIX-00-000400	SV-268101r1131004_rule	2025-08-19	1

Description
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. Satisfies: SRG-OS-000046-GPOS-00022, SRG-OS-000343-GPOS-00134

ℹ️ Check
Verify NixOS notifies the SA and ISSO (at a minimum) when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage capacity with the following command: $ sudo grep -w space_left_action /etc/audit/auditd.conf space_left_action = syslog If the "space_left_action" parameter is missing, commented out, or set to blanks, this is a finding. If the "space_left_action" is set to "syslog", the system logs the event, but does not generate a notification, this is a finding. If the "space_left_action" is set to "exec", the system executes a designated script. If this script does not inform the SA of the event, this is a finding. If the "space_left_action" is set to "email" check the value of the "action_mail_acct" parameter with the following command: $ sudo grep action_mail_acct /etc/audit/auditd.conf action_mail_acct root@localhost The "action_mail_acct" parameter, if missing, defaults to "root". If the "action_mail_acct" parameter is not set to the email address of the SA and/or ISSO, this is a finding. Note: If the email address of the SA is on a remote system, a mail package must be available.

ℹ️ Check

Verify NixOS notifies the SA and ISSO (at a minimum) when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage capacity with the following command: $ sudo grep -w space_left_action /etc/audit/auditd.conf space_left_action = syslog If the "space_left_action" parameter is missing, commented out, or set to blanks, this is a finding. If the "space_left_action" is set to "syslog", the system logs the event, but does not generate a notification, this is a finding. If the "space_left_action" is set to "exec", the system executes a designated script. If this script does not inform the SA of the event, this is a finding. If the "space_left_action" is set to "email" check the value of the "action_mail_acct" parameter with the following command: $ sudo grep action_mail_acct /etc/audit/auditd.conf action_mail_acct root@localhost The "action_mail_acct" parameter, if missing, defaults to "root". If the "action_mail_acct" parameter is not set to the email address of the SA and/or ISSO, this is a finding. Note: If the email address of the SA is on a remote system, a mail package must be available.

✔️ Fix
Configure NixOS to initiate an action to notify the SA and ISSO (at a minimum) when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage capacity. If the space_left_action parameter is set to "syslog", make sure the event being logged generates a notification to the SA and ISSO. If the space_left_action parameter is set to "exec", make sure the command being executed notifies the SA and ISSO. If the space_left_action parameter is set to "email", set the action_mail_acct parameter to an email address for the SA and ISSO. Add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix: space_left_action = syslog For example, an updated configuration of 'environment.etc."audit/auditd.conf".text' would look like the following ('...' denoting that the 'environment.etc."audit/auditd.conf".text' configuration may have other options configured): environment.etc."audit/auditd.conf".text = [ '' ... space_left_action = syslog ... '' ]; Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch

✔️ Fix

Configure NixOS to initiate an action to notify the SA and ISSO (at a minimum) when allocated audit record storage volume reaches 75 percent of the repository maximum audit record storage capacity. If the space_left_action parameter is set to "syslog", make sure the event being logged generates a notification to the SA and ISSO. If the space_left_action parameter is set to "exec", make sure the command being executed notifies the SA and ISSO. If the space_left_action parameter is set to "email", set the action_mail_acct parameter to an email address for the SA and ISSO. Add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix: space_left_action = syslog For example, an updated configuration of 'environment.etc."audit/auditd.conf".text' would look like the following ('...' denoting that the 'environment.etc."audit/auditd.conf".text' configuration may have other options configured): environment.etc."audit/auditd.conf".text = [ '' ... space_left_action = syslog ... '' ]; Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch