TOP Command details

The top command is a common performance analysis tool in Linux. It can display the resource usage of various processes in the system in real time, similar to the Windows Task Manager.
The following describes how to use it.

• View the display result of top
  • Statistical information area
  • Process Information area
• Change display content

View the display result of top

The result of the top command is as follows:

Top-01:06:48 up, 1 user, load average: 0.06, 0.60, 0.48
Tasks: 29 total, 1 running, 28 sleeping, 0 stopped, 0 zombie
CPU (s): 0.3% us, 1.0% Sy, 0.0% Ni, 98.7% ID, 0.0% wa, 0.0% hi, 0.0% Si
Mem: 191272 k total, 173656 K used, 17616 K free, 22052 K Buffers
Swap: 192772 k total, 0 K used, 192772 K free, 123988 K cached

PID user PR Ni virt res shr s % CPU % mem time + command
1379 root 16 0 7976 2456 S 1980 0.7. 03 sshd
14704 root 16 0 2128 980 R 796 0.7. 72 top
1 root 16 0 1992 632 s 544 0.0. 90 init
2 root 34 19 0 0 s 0.0 0.0. 00 ksoftirqd/0
3 root RT 0 0 0 s 0.0 0.0. 00 watchdog/0
 

Statistical information area

The first five lines are the overall statistics of the system. The first line is the task queue information, which is the same as the execution result of the uptime command. The content is as follows:

01:06:48	Current Time
Up :22	System running time, in the format of minutes
1 user	Current Login User count
Load average: 0.06, 0.60, 0.48	System load, that is, the average length of the task queue. The three values are the average values from 1 minute, 5 minutes, and 15 minutes ago to the present.

Second and Third, information about the process and CPU. When multiple CPUs exist, the content may exceed two rows. The content is as follows:

Tasks: 29 Total	Process count
1 running	Number of Running Processes
28 sleeping	Number of sleep Processes
0 stopped	Number of stopped Processes
0 zombie	Number of zombie Processes
CPU (s): 0.3% us	CPU usage percentage of user space
1.0% SY	CPU usage of kernel space
0.0% Ni	CPU usage percentage of processes that have changed their priorities in the process space
98.7% ID	Idle CPU percentage
0.0% wa	Percentage of CPU time waiting for Input and Output
0.0% hi
0.0% Si

Memory information of the last two behaviors. The content is as follows:

Mem: 191272 k total	Total physical memory
173656 K used	Total physical memory used
17616 K free	Total idle memory
22052 K Buffers	Memory Used as kernel Cache
Swap: 192772 k total	Total number of swap Areas
0 k used	Total number of swap zones used
192772 K free	Total number of idle swap Areas
123988 K cached	The total number of buffer swap areas. The content in the memory is swapped out to the swap zone and then into the memory, but the used swap zone has not been overwritten, The value isThe content already exists in the memory. The size of the swap area. When the corresponding memory is swapped out again, you do not have to write data to the swap zone.

Process Information area

The details of each process are displayed at the bottom of the statistics area. First, let's take a look at the meaning of each column.

Serial number	Column name	Description
A	PID	Process ID
B	Ppid	Parent process ID
C	Ruser	Real User Name
D	UID	User ID of the process owner
E	User	User Name of the process owner
F	Group	Group Name of the process owner
G	Tty	The terminal name of the startup process. Processes not started from the terminal are displayed?
H	PR	Priority
I	Ni	Nice value. A negative value indicates a high priority, and a positive value indicates a low priority.
J	P	The last CPU used is only meaningful in multiple CPU environments.
K	% CPU	CPU usage from the last update to the present
L	Time	Total CPU time used by the process, in seconds
M	Time +	Total CPU time used by the process, in 1/100 seconds
N	% Mem	Process UsedPhysical memory Percentage
O	Virt	Total virtual memory used by the process, in KB. Virt = swap + Res
P	Swap	In the virtual memory used by the process, the swap size, in KB.
Q	Res	Physical memory used by the process, not swapped out, in KB. Res = code + Data
R	Code	ExecutableCodeOccupiedPhysical Memory size, in KB
S	Data	Occupied by parts other than executable code (Data Segment + stack)Physical Memory size, in KB
T	SHR	Size of shared memory, in KB
U	Nflt	Page error count
V	MCM t	The number of pages that have been modified since the last write to the present.
W	S	Process status. D = Uninterrupted sleep R = Run S = Sleep T = Trail/stop Z = Zombie Process
X	Command	Command name/command line
Y	Wchan	If the process is sleeping, the system function name displayed in sleep
Z	Flags	Task flag, refer to sched. h

By default, only important PID, user, PR, Ni, virt, res, SHR, S, % CPU, % MEM, time +, and command columns are displayed. You can use the shortcut keys below to change the display content.

Change display content

PassF
Key to select the displayed content. Press F to display the column list. Press A-Z to display or hide the corresponding column, and press enter to confirm.

PressO
The key can change the Column Display sequence. A lower-case a-Z can move the corresponding column to the right, while an upper-case A-Z can move the corresponding column to the left. Press enter.

In upper caseF
OrO
And then press a-Z to sort the process by the corresponding column. In upper caseR
The key can reverse the current sorting.