Linux systems can view information such as CPU, memory, run time, swap partitions, thread of execution of the system through the top command.The top command is an effective way to find out what's wrong with your system.Not enough memory, not enough CPU processing power, too high IO reading and writing....

[root@foundation6 docker]# top

top - 21:31:26 up 15:16,  5 users,  load average: 0.61, 0.82, 0.75
Tasks: 240 total,   2 running, 238 sleeping,   0 stopped,   0 zombie
%Cpu(s): 13.7 us,  1.5 sy,  0.0 ni, 84.2 id,  0.6 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  3775264 total,   250100 free,  2495300 used,  1029864 buff/cache
KiB Swap:  4064252 total,  2789544 free,  1274708 used.   527664 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND    
16507 kiosk     20   0 1935284 201988  10816 R  46.8  5.4  68:11.92 plugin-con+
15773 kiosk     20   0 1784208 497692  40776 S   4.7 13.2  37:05.32 firefox    
  408 root      20   0   36940   4116   3920 S   3.0  0.1   4:51.67 systemd-jo+
 3789 kiosk     20   0  747664  14124   4696 S   2.0  0.4   2:49.76 gnome-term+
 2404 root      20   0  439488 106688  84580 S   1.7  2.8  16:08.35 Xorg       
 2662 kiosk      9 -11  700096   5232   3032 S   1.7  0.1   5:17.25 pulseaudio 
21632 kiosk     20   0  812940 167440  30100 S   1.7  4.4  20:15.48 wps        
 2688 kiosk     20   0 2111764 218776  18580 S   1.3  5.8  20:25.33 gnome-shell
  663 root      20   0  399976   3352   2984 S   1.0  0.1   0:46.92 rsyslogd   
 7349 qemu      20   0 1697464 956932    556 S   0.7 25.3   5:03.80 qemu-kvm   
 7803 qemu      20   0 1697460 708164    544 S   0.7 18.8   4:16.74 qemu-kvm   
   18 root      20   0       0      0      0 S   0.3  0.0   0:16.94 rcuos/0    
   19 root      20   0       0      0      0 S   0.3  0.0   0:18.43 rcuos/1    
   21 root      20   0       0      0      0 S   0.3  0.0   0:19.62 rcuos/3    
  671 root      20   0  207984    160    120 S   0.3  0.0   0:01.60 abrt-watch+
 5676 root      20   0       0      0      0 S   0.3  0.0   0:00.28 kworker/u1+
    1 root      20   0  189128   2900   1432 S   0.0  0.1   0:06.11 systemd    

The first line of the top command:

top - 21:31:26 up 15:16,  5 users,  load average: 0.61, 0.82, 0.75

Corresponds in turn: the current time of the system up system so far i run time, the number of users currently logged on to the system, the three numbers after load average represent the load of one minute, five minutes, and fifteen minutes, respectively.
Note: The load average data is the number of active processes that are checked every five seconds and then calculated according to a particular algorithm.If this number is divided by the number of logical CPU s, a result higher than 5 indicates that the system is overloaded.

top Second line of command:
Tasks: 240 total,   2 running, 238 sleeping,   0 stopped,   0 zombie

Tasks represent tasks (processes), 240 total represents 240 processes, of which 2 are running, 238 are dormant (suspended), stopped is stopped, and zombie is zombie is zero.

The third line of the top command, cpu status:

%Cpu(s): 13.7 us,  1.5 sy,  0.0 ni, 84.2 id,  0.6 wa,  0.0 hi,  0.0 si,  0.0 st

Correspond in turn: percentage of user space occupied by cpu, percentage of kernel space occupied by cpu, percentage of CPU occupied by processes that have changed priority, percentage of idle cpu, percentage of CPU occupied by IO waiting, percentage of CPU occupied by hard interrupt (Hardware IRQ), percentage of CPU occupied by soft interrupt - software
top command line 4, memory state:

KiB Mem :  3775264 total,   250100 free,  2495300 used,  1029864 buff/cache

Correspond in turn: total physical memory (3.7G), total free memory (2.5G), total in-use memory (2.4G), buffer memory
The total amount of memory in use in the fourth line refers to the number of memory currently controlled by the system's kernel, and the total amount of free memory refers to the number of memory that the kernel has not yet been brought under its control.Kernel-managed memory isn't necessarily in use, but also used memory that can now be reused. The kernel doesn't return this reusable memory to free, so free memory on linux will get smaller and smaller, but don't worry about it
top command line 5, swap swap partition:

KiB Swap:  4064252 total,  2789544 free,  1274708 used.   527664 avail Mem 

Correspond in turn: total exchange area (4G), total free exchange area (2.7G), total used exchange area (1.2G), total available exchange area

For memory monitoring, we need to monitor the use of the swap swap partition on the fifth line all the time in top. If this value keeps changing, it means that the kernel is constantly swapping data between memory and swap, which is really not enough memory.

top command line 6 is empty

top command line 7, monitoring of processes:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND    

Correspond in turn:
PID - Process id
USER - Process Owner
PR - Process Priority
NI-nice value.Negative values indicate high priority and positive values indicate low priority
VIRT - The total amount of virtual memory used by the process in kb.VIRT=SWAP+RES
RES - The size of physical memory used by a process and not swapped out in kb.RES=CODE+DATA
SHR - Shared memory size in kb
S - Process state.D=Uninterrupted Sleep State R=Run S=Sleep T=Track/Stop Z=Zombie Process
%CPU - Percentage of CPU time consumed since last update
%MEM - Percentage of physical memory used by the process
TIME+ - Total CPU time used by a process in 1/100 seconds
COMMAND - Process name (command name/command line)