EX200 Operate running systems Practice Question
Which three commands can be used to display overall memory usage information?
⚠ Common exam trap
Red Hat often tests the distinction between commands that show per-process memory (like ps aux) versus those that show system-wide memory totals (like free, top, vmstat), leading candidates to incorrectly select ps aux as a memory usage command.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
free
The 'free' command displays the total, used, and available physical and swap memory on the system. It reads /proc/meminfo and presents a concise summary of memory usage, making it a primary tool for checking overall memory consumption.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
free
Why this is correct
`free` is a dedicated memory-reporting utility that reads from `/proc/meminfo` and displays a concise summary of total, used, free, shared, buff/cache, and available physical memory, along with swap usage. Modern versions emphasize the `available` field, which estimates how much memory can be allocated without swapping, unlike the more misleading `free` column. This makes `free` a straightforward and accurate command for quickly checking overall memory utilization.
- ✗
uptime
Why it's wrong here
The `uptime` command displays the current time, how long the system has been running, how many users are logged on, and the system load averages for 1, 5, and 15 minutes. Because it reports only processor load queue information and no memory counters, it cannot show overall memory utilization. While a high load average might indirectly correlate with memory pressure, uptime never reads from `/proc/meminfo`, so it is not a valid tool for this task.
- ✓
top
Why this is correct
`top` provides a real-time, interactive view of system health, with a five-line summary at the top that shows total, used, and free physical memory, as well as buff/cache and available memory. The process list beneath the summary details per-process memory consumption and includes a `%MEM` column, but the header's "KiB Mem" line is the system-wide overall memory usage. Because it refreshes continuously, it can reveal changing memory utilization dynamically, making it an appropriate choice for monitoring overall memory.
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ps aux
Why it's wrong here
The `ps aux` command lists every process on the system with columns such as `%MEM`, `RSS`, and `VSZ`, which are per-process memory metrics obtained from `/proc/<pid>/statm` and `/proc/<pid>/status`. It does not aggregate these numbers to show a single system-wide total of used or free memory, nor does it include system-level caches and buffers in a summary line. Summing the RSS values manually would double-count shared pages and ignore kernel memory, so `ps aux` is not reliable for reporting overall memory usage.
- ✓
vmstat
Why this is correct
The `vmstat` command, when run with no arguments, prints a single system-wide summary followed by periodic snapshots; the memory portion reports free memory, buffered memory, cache, and swap in/out activity. With `-a`, it displays inactive and active memory, and with `-s`, it gives a detailed table of memory statistics from `/proc/meminfo`. Because it provides both memory and swap totals alongside CPU and I/O metrics, it is a valid command for viewing overall memory usage.
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