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top

The top command allows you to dynamically view the overall operation of the system in real time. It is a practical tool that combines multiple information monitoring system performance and operational information. It provides a dynamic and interactive real-time view that displays overall performance information of the system and relevant information about running processes.

Syntax​

top -hv | -bcEHiOSs1 -d secs -n max -u|U user -p pid(s) -o field -w [cols]

Option Explanation​

  • -b: Run in batch mode and directly output the results to a file.
  • -c: Display the complete command line without truncation.
  • -d <seconds>: Screen refresh interval time.
  • -I: Ignore idle processes.
  • -s: Secure mode.
  • -S: Accumulatively display the CPU usage time of processes.
  • -i: Do not display idle or useless processes.
  • -u <username>: Specify the username.
  • -p <pid>: Specify the process.
  • -n <number>: Number of times to loop display.
  • -H: Display resource occupation of all threads.

top Interactive Commands​

Some interactive commands that can be used during the execution of the top command. These commands are single-letter, and if the -s option is used in the command line, some commands may be blocked.

  • h: Display the help screen, providing a brief summary of commands.
  • k: Terminate a process.
  • i: Ignore idle and zombie processes (toggle command).
  • q: Quit the program.
  • r: Reschedule the priority of a process.
  • S: Switch to cumulative mode.
  • s: Change the delay time between two refreshes, in seconds (if decimals are used, in milliseconds). Entering a value of 0 will continuously refresh the system. The default value is 5 seconds.
  • f or F: Add or remove items from the current display.
  • o or O: Change the order of displayed items.
  • l: Switch to display average load and boot time information.
  • m: Switch to display memory information.
  • t: Switch to display process and CPU status information.
  • c: Switch to display command names and complete command lines.
  • M: Sort by resident memory size.
  • P: Sort by CPU usage percentage.
  • T: Sort by time/accumulative time.
  • w: Write current settings to the ~/.toprc file.

Display Information​

top - 14:55:57 up  1:03,  2 users,  load average: 0.62, 0.55, 0.45
Tasks: 158 total,   1 running, 157 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.7 us,  9.3 sy,  0.0 ni, 86.0 id,  0.0 wa,  0.0 hi,  0.9 si,  0.0 st
MiB Mem :   1982.2 total,    778.4 free,    645.6 used,    558.1 buff/cache
MiB Swap:      0.0 total,      0.0 free,      0.0 used.   1307.2 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   4496 root      20   0   14660   3092   2628 R  23.8   0.2   0:00.13 top
   3032 root      20   0       0      0      0 S  14.3   0.0   0:26.43 RTW_CMD_THREAD
      1 root      20   0  167580  10200   7216 S   0.0   0.5   0:03.09 systemd
      2 root      20   0       0      0      0 S   0.0   0.0   0:00.00 kthreadd
      4 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 kworker/0:0H
      6 root       0 -20       0      0      0 I   0.0   0.0   0:00.00 mm_percpu_wq
      7 root      20   0       0      0      0 S   0.0   0.0   0:00.13 ksoftirqd/0

System Information:

  • uptime: The system's uptime and average load.
  • tasks: The number of running processes and sleeping processes.
  • CPU: The overall CPU usage and usage of each core.
  • Memory: The overall memory usage, free memory, and memory used for buffering and caching.

Process Information:

  • PID: The process identifier.
  • USER: The username of the running process.
  • PR (Priority): The priority of the process.
  • NI (Nice Value): The priority adjustment value of the process.
  • VIRT (Virtual Memory): The size of the process's virtual memory.
  • RES (Resident Memory): The amount of physical memory actually used by the process.
  • SHR (Shared Memory): The amount of memory shared by the process.
  • %CPU: The percentage of CPU usage by the process.
  • %MEM: The percentage of memory usage by the process.
  • TIME+: The cumulative CPU time of the process.

Features and Interactions:

  • Key Commands: When running top, certain key commands can be used for operations, such as pressing "k" to terminate a process and pressing "h" to display help information.
  • Sorting: Processes can be sorted by CPU usage, memory usage, process ID, etc.
  • Refresh Rate: The refresh rate of top can be set to dynamically view system information.

Common Commands​

Display Process Information

top

Show the complete command

top -c

Display program information in batch mode

top -b

Display program information in cumulative mode

top -S

Set the number of information updates

top -n 2   # means stop updating display after 2 updates

Set the information update interval

top -d 3  # means update every 3 seconds

Display specific process information

top -p 139  # display process information for process number 139, including CPU and memory usage

Exit after 10 updates

top -n 10

Users will not be able to use interactive commands to control processes

top -s