Understanding Linux System Performance Metrics

CPU and Memory Utilization

• The % of time the CPU has been idle
• The % of time the CPU has been waiting for I/O
• The % of CPU time spent servicing hard interrupts
• The % of CPU time spent servicing soft interrupts
• The % of CPU time stolen from the current vm by the hypervisor

Memory Utilization

• 4 KiB Mem: The amount of RAM being used in kilobytes
• 5 KiB Swap: The amount of swap space (virtual memory) being used in kilobytes

Top Program Header

• PID: Process ID
• USER: Username under which the process is running
• PR: Priority for the process, ranging from -20 (very important) to 19 (unimportant)
• NI: Niceness value, negative increases priority, positive decreases priority
• VIRT: Total amount of virtual memory used by the process
• RES: Resident size in kb, non-swapped physical memory used by the process
• SHR: Shared memory size in kb, memory that could be allocated to other processes
• S: Process status
• %CPU: Percentage of CPU time the process was using at the time top last updated
• %MEM: Percentage of memory the process was using at the time top last updated
• TIME+: Cumulative CPU time the process and children of the process have used
• COMMAND: Name of the process or path to the command used to start the process

Controlling Processes

• To interrupt a process, press Ctrl + C

Processes Characteristics

• Can be started from the GUI or the command line
• Can start another process
• Can only be created by another process

Commands Used in Viewing and Controlling Processes

• ps: Reports a snapshot of current processes
• top: Displays tasks
• jobs: Lists active jobs
• bg: Places a job in the background
• fg: Places a job in the foreground

Viewing Processes

• ps Command:
  • Process States:
    • R: Running
    • S: Sleeping (waiting for an event)
    • D: Uninterruptible sleep (waiting for I/O)
    • T: Traced or stopped
    • Z: A defunct or “zombie” process (child process that has been terminated, but not cleaned up by its parent)
  • Characters used with Process States:
    • <: High priority process
    • N: Low priority process
    • L: Has pages locked into memory (for real-time and custom I/O)
    • s: A session leader
    • l: Multi-threaded
    • +: In the foreground process group

ps Command with the aux option

• Header Meaning:
  • USER: User ID, owner of the process
  • %CPU: CPU usage in percent
  • %MEM: Memory usage in percent
  • VSZ: Virtual Memory Size
  • RSS: Resident Set Size, amount of physical memory (in kilobytes) the process is using
  • START: Time when the process has started

Top Program System Summary

• Row Field 1:
  • Up: Uptime, amount of time since the machine was last booted
  • User: Number of users logged in
  • Load average: Number of processes waiting to run (in a runnable state and sharing the CPU)
  • Tasks: Number of processes and their various process states
  • %Cpu(s): CPU usage:
    • us: User processes
    • sy: System (kernel) processes
    • ni: “nice” (low priority) processes
    • id: Idle time
    • wa: Waiting for I/O
    • hi: Hardware interrupts
    • si: Software interrupts
    • st: Stolen time (from the hypervisor)