NixOS must have time synchronization enabled.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-268151	SRG-OS-000356-GPOS-00144	ANIX-00-001440	SV-268151r1131103_rule	2025-08-19	1

Description
Inaccurate time stamps make it more difficult to correlate events and can lead to an inaccurate analysis. Determining the correct time a particular event occurred on a system is critical when conducting forensic analysis and investigating system events. Synchronizing internal information system clocks provides uniformity of time stamps for information systems with multiple system clocks and systems connected over a network. Organizations should consider setting time periods for different types of systems (e.g., financial, legal, or mission-critical systems). Organizations should also consider endpoints that may not have regular access to the authoritative time server (e.g., mobile, teleworking, and tactical endpoints). This requirement is related to the comparison done every 24 hours in SRG-OS-000355 because a comparison must be done to determine the time difference.

Description

Inaccurate time stamps make it more difficult to correlate events and can lead to an inaccurate analysis. Determining the correct time a particular event occurred on a system is critical when conducting forensic analysis and investigating system events. Synchronizing internal information system clocks provides uniformity of time stamps for information systems with multiple system clocks and systems connected over a network. Organizations should consider setting time periods for different types of systems (e.g., financial, legal, or mission-critical systems). Organizations should also consider endpoints that may not have regular access to the authoritative time server (e.g., mobile, teleworking, and tactical endpoints). This requirement is related to the comparison done every 24 hours in SRG-OS-000355 because a comparison must be done to determine the time difference.

ℹ️ Check
Verify NixOS synchronizes internal information system clocks to the authoritative time source when the time difference is greater than one second with the following command: $ grep -iR timesyncd.enable /etc/nixos/ services.timesyncd.enable = true; If "services.timesyncd.enable" is not set to "true", is commented out, or is missing, this is a finding.

✔️ Fix
Configure NixOS to regularly synchronize the system clock. Add the following Nix code to the NixOS Configuration, usually located in /etc/nixos/configuration.nix or /etc/nixos/flake.nix: services.timesyncd.enable = true; Rebuild and switch to the new NixOS configuration: $ sudo nixos-rebuild switch