Which statement is true regarding FortiGate firmware upgrades?

The statement about retaining all policies during a firmware upgrade is indeed correct. When performing a firmware upgrade on a FortiGate device, the system is designed to preserve the configuration and policy settings. This ensures that after the upgrade, the existing firewall rules, security profiles, and other configurations remain intact, allowing the device to continue functioning without requiring reconfiguration. This feature is essential for operational continuity, as it minimizes downtime and simplifies the upgrade process, enabling administrators to maintain their security posture through updates.

While there are other aspects related to firmware upgrades, such as command line execution or the timing of the upgrade in relation to production hours, these are not true universally across all scenarios. Therefore, the ability to retain all policies simplifies the upgrade process and alleviates concerns about losing configuration data during maintenance.