A Guide to Virtual Memory Statistics Reporting
Overview
vmstat is a command-line utility that provides detailed reports on your system’s processes, memory usage, paging activities, I/O operations, system events, disk activity, and CPU performance. It’s an invaluable tool for monitoring the health and performance of your system’s virtual memory.
The utility’s initial report offers averages since the last system reboot, while subsequent reports can be generated at specified intervals, providing real-time insights into your system’s performance.
How to Use vmstat
To utilize vmstat, the syntax is straightforward: vmstat [options] [delay [count]]. Without specifying a delay, vmstat will produce a single report with averages since the last reboot. When a delay is included, vmstat generates reports at that interval, offering continuous monitoring.
Key Options
- delay: Sets the time between each update/report in seconds.
- count: Determines how many updates/reports to generate. Without a count and when a delay is specified, vmstat will continue indefinitely.
Significant flags include:
-a: Shows active/inactive memory.-f: Displays fork count since boot.-m: Reveals slabinfo, detailed kernel cache information.-n: Prevents the header from repeating in every report.-s: Summarizes event counters and memory stats.-d: Offers disk statistics.-D: Summarizes disk activity.-p: Provides detailed statistics for a specific partition.-S: Allows you to select the unit of measurement for reporting.-t: Adds a timestamp to each line of the report.-w: Enables wide output mode.-V: Displays version information.-h: Offers help and usage information.
Field Descriptions
- Processes (
Procs): Reports on runnable and sleeping processes. - Memory: Details virtual memory usage, including free, buffered, and cached memory.
- Swap: Provides swap memory statistics.
- I/O (
IO): Shows block device I/O statistics. - System: Reports on system interrupts and context switches.
- CPU: Breaks down CPU time by user, system, idle, I/O wait, and stolen time.
Disk and Partition Reporting
For disk and partition modes, vmstat can detail reads and writes, including total operations, sectors read/written, and time spent on I/O operations.
Slab Allocator Reporting (-m option)
In slab mode, vmstat lists active objects, total objects, object size, and pages occupied by these objects, offering a deep dive into kernel cache management.
Practical Applications
Vmstat’s real power lies in its ability to report system performance metrics in real-time, making it an essential tool for system administrators and performance analysts. Whether you’re diagnosing a slow system, planning capacity, or just curious about your system’s internals, vmstat provides a comprehensive overview without needing special permissions.
Conclusion
By leveraging vmstat, users gain a powerful tool for monitoring and diagnosing system performance issues related to virtual memory. Its flexibility in reporting intervals and detailed statistics make it indispensable for maintaining system health and performance.