Top

Linux System Monitoring Commands #

Review

  1. 2020/04/15

This guide covers essential Linux system monitoring commands for analyzing system performance and resource usage.

1. top - Process Activity Monitor #

top（Time of Process）is a real-time system monitor that displays system summary information and a list of processes currently being managed by the Linux kernel.

Basic Usage #

top

top

Key Metrics #

  • CPU Usage:

    • %us: User space CPU usage (without nice scheduling)
    • %sy: System space CPU usage (kernel processes)
    • %ni: User space CPU usage with nice scheduling
    • %id: Idle CPU
    • %wa: CPU waiting for I/O operations
    • %hi: Hardware interrupt handling
    • %si: Software interrupt handling
    • %st: CPU stolen by virtual machine

  • Memory Usage:

    • Mem: Physical memory usage
    • Swap: Swap space usage

Interactive Commands #

  • P: Sort by CPU usage
  • M: Sort by memory usage
  • N: Sort by process ID
  • k: Kill a process
  • q: Quit top
  • 1: Toggle CPU core display

2. free - Memory Usage #

free displays the total amount of free and used physical and swap memory in the system.

brew install procps

Basic Usage #

free -h  # Human readable format
free -m  # Display in megabytes

Key Metrics #

  • total: Total installed memory
  • used: Used memory
  • free: Unused memory
  • shared: Memory used by tmpfs
  • buff/cache: Memory used by buffers and cache
  • available: Memory available for new applications

3. vmstat - Virtual Memory Statistics #

vmstat reports information about processes, memory, paging, block IO, traps, and CPU activity.

Basic Usage #

vmstat 1  # Update every second

# for macOS
vm_stat -c 5 1

Key Metrics #

  • Procs:
    • r: Running processes
    • b: Blocked processes
  • Memory:
    • swpd: Used swap space
    • free: Free memory
    • buff: Buffer memory
    • cache: Cache memory
  • Swap:
    • si: Swap in
    • so: Swap out
  • IO:
    • bi: Blocks in
    • bo: Blocks out
  • System:
    • in: Interrupts per second
    • cs: Context switches per second
  • CPU:
    • us: User time
    • sy: System time
    • id: Idle time
    • wa: I/O wait time
    • st: Stolen time

get free memory

vm_stat | perl -ne '/page size of (\d+)/ and $size=$1; /Pages free:\s+(\d+)/ and printf("Free Memory: %.2f MB\n", $1*$size/1048576)'

4. pmap - Process Memory Map #

pmap reports the memory map of a process, showing the memory usage of each segment.

brew install pmap

Basic Usage #

pmap -x <PID>  # Detailed memory map
pmap -d <PID>  # Display device format

Example #

# View memory usage of process with PID 5647
pmap -d 5647

Key Information #

  • Address space
  • Permissions
  • Offset
  • Device
  • Mapping name
  • Size
  • RSS (Resident Set Size)
  • Dirty pages
  • Referenced pages
  • Anonymous pages

Best Practices #

  1. Regular Monitoring:

    • Use top for real-time monitoring
    • Schedule regular checks with vmstat
    • Monitor memory usage with free

  2. Troubleshooting:

    • High CPU usage: Check top for process details
    • Memory issues: Use free and pmap
    • I/O bottlenecks: Monitor with vmstat

  3. Performance Optimization:

    • Identify memory-hungry processes with pmap
    • Track system resource trends
    • Monitor swap usage to prevent performance degradation

Remember to run these commands with appropriate permissions (usually as root or with sudo) for complete system information.