Linux top Command

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Linux topis a real-time system monitoring tool commonly used on Linux and other Unix-like systems. It provides a dynamic, interactive real-time view showing overall system performance information and information about running processes.

Permissions: All users.

Syntax

top [-] [d delay] [q] [c] [S] [s] [i] [n] [b]

Parameter Description：

  • -d <秒数>: Specifies the refresh time interval of the top command, in seconds.
  • -n <次数>: Specifies the number of runs after which the top command automatically exits.
  • -p <进程ID>: Display only information for the specified process ID.
  • -u <用户名>: Display only process information for the specified username.
  • -H: Display detailed thread information in the process information.
  • -i: Do not display idle or useless processes.
  • -b: Run in batch mode, directly outputting results to a file.
  • -c: Display the full command line without truncation.
  • -S: Accumulatively display the CPU time used by processes.

Display Information

Some common functions and display information of the top command:

Overall system information:

  • uptime: System uptime and average load.
  • tasks: Number of currently running processes and threads.
  • CPU: Overall CPU usage and per-core usage.
  • Memory: Overall memory usage, available memory, and cache.

Process information:

  • PID: Process identifier.
  • USER: Username of the user running the process.
  • PR (Priority): Process priority.
  • NI (Nice value): Process priority adjustment value.
  • VIRT (Virtual Memory): Size of virtual memory used by the process.
  • RES (Resident Memory): Size of physical memory actually used by the process.
  • SHR (Shared Memory): Size of memory shared by the process.
  • %CPU: CPU usage of the process.
  • %MEM: Memory usage of the process.
  • TIME+: Accumulated CPU time of the process.

Functions and interactive operations:

  • Key commands: While top is running, you can use some key commands to operate, such as pressing "k" to terminate a process, pressing "h" to display help information, etc.
  • Sorting: Processes can be sorted by CPU usage, memory usage, process ID, etc.
  • Refresh rate: You can set the refresh rate of top to view system information dynamically.

Examples

Display process information

# top

Display full 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

//表示更新两次后终止更新显示

Set the information update time

# top -d 3

//表示更新周期为3秒

Display specified process information

# top -p 139

//显示进程号为139的进程信息，CPU、内存占用率等

Exit after displaying updates ten times

top -n 10

The user will not be able to use interactive commands to control processes.

top -s

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