Top

Top is a general performance analysis tool in Linux. It displays the system load, memory usage, and resource usage of each process in real time.

You can run the top command to show the overall situation of the system. Here is an example:

top - 17:51:14 up 69 days, 20:06,  2 users,  load average: 71.81, 71.99, 63.46
Tasks: 1335 total,   1 running, 1334 sleeping,   0 stopped,   0 zombie
%Cpu(s): 34.9 us,  6.0 sy,  0.1 ni, 58.9 id,  0.0 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem : 79180025+total, 53055686+free, 16692761+used, 94315792 buff/cache
KiB Swap:        0 total,        0 free,        0 used. 61829075+avail Mem

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 52974 hudson    20   0  160.1g 146.3g  73796 S  3893 19.4   1273:28 observer
 33773 root      39  19  764452 104396   4408 S   8.2  0.0  14:55.16 bianque_daemon_
  8951 root      20   0 3398328  16880   3284 S   4.3  0.0   1787:32 y_watchdog
 11959 root      10 -10  247688 107284   4508 S   3.9  0.0   4226:29 AliYunDun
  9321 root      20   0  577532  79328   4264 S   3.0  0.0   1074:18 asar
 98164 hudson    20   0  159020   3560   1572 R   1.6  0.0   0:00.14 top
 95053 root      16  -4 1936116  72160   4460 S   1.3  0.0   2699:29 h2o
 97939 root      20   0  169488  24716    788 S   1.3  0.0   0:00.13 vsar
  2529 root      20   0  162396  14628   2148 S   1.0  0.0 453:31.03 ob-sm-probe
 51856 root      39  19 2215292  56896   4072 S   1.0  0.0 561:25.46 argusage

• The first line shows the overall situation of the system.

  Specifically, it shows the current system time, the length of system uptime (up) since the last boot, the number of online users, and the average CPU load information over the last 1 minute, 5 minutes, and 15 minutes, respectively.

• The second line shows information about the tasks in the system.

  Specifically, it shows the total number of tasks, the number of running processes, the number of sleeping processes, the number of stopped processes, and the number of zombie processes.

• The third line shows the CPU state percentages on the server.

  Specifically, it shows the percentages of time of running un-niced user processes (us), time of running kernel processes (sy), time of running niced user processes (ni), time spent on the kernel idle handler (id), time of waiting for I/O completion (wa), time spent on servicing hardware interrupts (hi), and time spent on servicing software interrupts (si).

  To show or hide the information of each CPU, press 1. Here is an example:

  %Cpu0  : 24.3 us,  0.0 sy,  0.7 ni, 75.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu1  : 30.7 us,  0.7 sy,  1.0 ni, 67.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu2  : 40.7 us,  0.3 sy,  0.0 ni, 58.6 id,  0.0 wa,  0.0 hi,  0.3 si,  0.0 st
  %Cpu3  : 39.1 us,  0.3 sy,  0.0 ni, 60.6 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu4  : 46.5 us,  0.0 sy,  0.0 ni, 53.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu5  : 10.6 us,  0.3 sy,  0.3 ni, 88.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  

• The fourth line shows information about the physical memory of the system.

  Specifically, it shows the total physical memory (total), free physical memory (free), used physical memory (used), and cached physical memory (buff/cache) in kibibytes (KiB).

• The fifth line shows the memory information in the swap file.

  Specifically, it shows the total memory, free memory, used memory, and the estimated available memory in the swap file in KiB.

• Starting from the seventh line, the information about each process is shown.

  • PID: the ID of a process.
  • USER: the owner of a process.
  • PR: the priority of a process. The smaller the value, the higher the priority.
  • NI: the Nice value of a process. A positive value indicates a low priority, a negative value indicates a high priority, and the value 0 indicates that the priority of the process will not be adjusted.
  • VIRT: the virtual memory used by a process.
  • RES: the physical memory occupied by a process.
  • SHR: the shared memory used by a process.
  • S: the status of a process. S indicates that the process is in hibernation. R indicates that the process is running. Z indicates that the process is a zombie process. N indicates that the priority value of the process is negative.
  • %CPU: the CPU utilization of a process.
  • %MEM: the percentage of physical memory used by the process in the total memory.
  • TIME+: the total CPU time that is occupied by the process after it starts, which indicates the accumulated CPU occupied time.
  • COMMAND: the name of the command used to start the process.

You may use the following options to obtain more information:

• H: specifies to display the thread information. You can use this option to view the status of each OBServer thread.

• P: specifies to sort the processes by CPU utilization.

• M: specifies to sort the processes by memory usage.

• I: specifies to display ongoing processes.

• O: specifies to add a filter. For example, COMMAND:observer returns only processes with the process name observer. It also applies to thread filtering, such as COMMAND:RpcIO.