The vmstat command is a standard Linux utility designed to report virtual memory statistics, which includes information about processes, memory, paging, block IO, traps, and CPU activity. The command's syntax is vmstat [options] [delay [count]]. The delay parameter specifies the time interval between updates in seconds. Therefore, executing vmstat 5 will display system memory and CPU load statistics, refreshing the output every 5 seconds until interrupted. This directly and efficiently satisfies all requirements of the question.

A. watch -t 5 vmstat: The -t option for watch turns off the header display; it does not set the time interval. The correct option for interval is -n.

C. vmstat -t 5: While this command would run with a 5-second interval, the -t option adds a timestamp, which was not requested. vmstat 5 is the most direct and accurate answer.

D. watch uptime: The uptime command provides system load averages but does not offer the detailed memory statistics (e.g., free, buffer, cache) that vmstat provides.

E. watch -n 10 vmstat: This command sets the update interval to 10 seconds, not the 5 seconds required by the question.

1. Official Vendor Documentation (Linux Man Page): The vmstat(8) manual page is the authoritative source for the command's usage. It states: "vmstat reports information about processes, memory, paging, block IO, traps, disks and cpu activity. ... vmstat [options] [delay [count]] ... The delay is the time between updates in seconds." This confirms that vmstat 5 sets a 5-second delay.

Source: vmstat(8) — Linux manual page. Available via any standard Linux distribution or online archives like man7.org.

2. Official Vendor Documentation (Forescout): Forescout appliances run a hardened Linux-based operating system. The Forescout Administration Guide references the use of standard Linux commands via the CLI for troubleshooting and monitoring system performance, including CPU and memory.

Source: Forescout Platform and Base Modules Administration Guide, Version 8.4.2, "CLI Commands" section, Page 637. (Note: While it lists general CLI access, the use of standard Linux tools like vmstat is implicit for system-level diagnostics).

3. University Courseware: Reputable computer science and system administration courses cover standard performance monitoring tools. These materials consistently describe vmstat's delay parameter as the method for setting refresh intervals.

Source: University of Chicago, CMSC 23200/33200: Introduction to Computer Security, Winter 2014, Lab 2: "Tools like top, vmstat, and iostat are your friends. For example, vmstat 5 will give you a snapshot of system performance every 5 seconds."