Detailed explanation of top and free commands

top command

In the O & M interview top Commands are asked more frequently than other commands , because top It is too important for the operation and maintenance personnel , It can not only be used to view process information 、CPU、 Memory 、 System status, etc . The operation and maintenance personnel can maintain the system accordingly .

// In this interface , Use P In order to CPU Use case to sort ;M To sort by memory usage ;N In order to PID To sort and display ;T It is displayed in the cumulative sorting of process usage time ;k To someone pid A signal , To kill the process ;r To someone pid Re customize one nice value ( That is what we often call priority );q Is used to exit top The interaction mode of

// This is top Command output content , Some people will feel very confused , Actually top The command can view the content you want to view according to the parameters

Parameters	effect
-d	Specify the time interval between every two screen information refreshes .
-p	By specifying the monitoring process ID To just monitor the status of a process .
-q	This option will make the top Refresh without any delay .
-S	Specify the cumulative mode
-s	send top The command runs in safe mode . This will remove the potential danger of interactive commands .
-i	send top Do not show any idle or zombie processes
-c	Show the entire command, not just the command name

// When you are in top Interactive mode of press 1 It can monitor every logic of you CPU The state of

// Press f You can enter this view , Press q You can exit this view

// Press ”shift+>” perhaps ”shift+<” It can be done to "%CPU" Sort

top The first line of the command

// The first line is task queue information

• 21:50:47 Indicates the current system time
• up 6:26 It indicates how long the current system has been running , The format is , Hours ： minute
• 2 users Indicates the number of users currently logged in to the system
• load average: 0.00, 0.00, 0.00 This represents the system load , That is, the average length of the task queue . All three values are 1 minute , The smaller the three values, the better , The system load is low in Yueming , higher than 5 It means that the system is heavily loaded .

top The second line of the command

// The second line represents the process information of the system

• 208 total Represents the total number of processes in the current system
• 1 running Indicates the number of processes currently running in the system
• 207 sleeping Indicates the number of current system sleep processes
• 0 stopped Indicates the number of processes stopped by the current system
• 0 zombie Indicates the number of zombie processes in the current system

top The third line of the command

// The third line represents the system CPU Information about

• 0.0 us Indicates the occupancy of user space CPU Percent of
• 0.2 sy Indicates the kernel space occupation CPU Percent of
• 0.0 ni It indicates that the priority of the process in the user process space has been changed CPU percentage
• 99.8 id I'm free CPU percentage
• 0.0 wa Waiting for input and output CPU Time percentage
• 0.0 hi Indicates hard interrupt occupancy CPU Percent of
• 0.0 si Indicates soft interrupt occupancy CPU Percent of
• 0.0 st For virtual CPU The situation of , Indicates that the virtual machine has stolen CPU Time

top The fourth line of the command

// The fourth line is the memory information of the system

• 1800.6 total Represents the total amount of physical memory
• 1010.9 free Indicates the total amount of free memory
• 382.3 used Indicates the total amount of physical memory used
• 407.5 buff/cache Indicates the amount of memory used as the kernel cache

top The fifth line of the command

// The fifth line shows the information of the exchange partition of the system

• 2092.0 total Indicates the total number of swap partitions
• 2092.0 free Indicates the total number of free swap areas
• 0.0 used Indicates the total number of swap partitions used
• 1255.4 avail Mem Represents the amount of physical memory that can be used for the next allocation of the process

top The sixth line of the command

• PID Represents the of the process id
• USER Which user owns the process
• PR Indicates priority
• NI nice Values are all our priorities , Negative values have high priority , Positive values have a lower priority than negative values
• VIRT Total virtual memory used by the process , Unit is kb,VIRT=SWAP( Swap partition )+RES
• RES Represents the 、 Physical memory size not swapped out , Unit is kb.RES=CODE+DATA
• CODE Represents the physical memory occupied by executable code , Unit is kb.
• SHR Indicates the size of the shared memory , The unit is also kb
• S Represents the state of the process .D= Uninterrupted sleep ;R= function ’;S= sleep ;T= track / stop it ;Z= Zombie process
• %CPU It represents the last update to the present CPU Percentage of time used
• %MEM Represents the percentage of physical memory used by the process
• TIME+ Represents the process used CPU Total time , Company 1/100 second
• COMMAND Indicates the command name / Command line
• WCHAN Indicates if the process is sleeping , The system function name in sleep is displayed
• nFLT Number of page errors
• nDRT Last write to now , Number of pages modified .

free command

// free The command is used to view the system memory , But in a static way top The orders are different .free Command is also one of the most frequently asked commands in the O & M interview

[[email protected] ~]# free 
              total        used        free      shared  buff/cache   available
Mem:        1843864      390628     1035936        8888      417300     1286336
Swap:       2142204           0     2142204

• total Indicates the total amount of memory , Total physical memory
• used The amount of memory used
• free Represents the amount of free memory
• shared Total memory shared by multiple processes
• buff/cache Number of cache memory

// The relationship between the total amount of memory and the amount of used memory and free memory
total=used+free

There is another important point I don't have here, but I'll list it for you
-/+ buffers/cache

-buffers/cache： Is the amount of memory actually used
+buffers/cache： Amount of memory available .

-buffers/cache This is actually the memory actually used by the process or service ; and +buffers/cache Is the total amount of memory available .

Parameters	effect
-b	Output to the screen in bytes
-k	With kb Output to the screen in the form of
-m	With mb Output to the screen in the form of
-g	With gibibytes Form output to the screen ( This gibibytes I don't understand )
-h	Output to the screen in a human readable manner
-l	Display detailed low memory and high memory statistics ( The simple point is that the output content is more detailed )
-t	Show total The sum of
-s	Output to the screen in seconds -s2, Output to the screen every two seconds
-c	How many times to print and then exit ,-c3, Is to print three times to the screen and then exit
-w	Interpreted as range output , Is to put buff/cache Output separately .
-V	see free Version information for , You can also use --version see

Here I will not demonstrate the specific use , You can try it yourself , Believe in yourself .