当前位置：网站首页>Process and scheduled task management

【 process ： The process of running a program , Is dynamic , It has life cycle and operation state , Concurrent multiple threads , Each thread performs a different task 】

Program , process , Thread relationship ：

Threads are contained in the process , Is the actual operation unit in the process , It is also the basic unit that can run independently in the operating system , Also known as lightweight process , Multiple threads can be concurrent in one process , Each thread can perform different tasks in parallel , The processes in the task manager are generated by the downloaded application , An application can also contain multiple processes .

2.ps View static process information

ps command ： View static process statistics

1)ps -aux： The process information will be displayed in the form of a simple list

-a： All process information under the current terminal

-u： Output process information in user oriented format

-x： Process information of the current user under all terminals

In the above output information , The first line is the title of the list , The meaning of each field is described as follows .

USER: The name of the user account that started the process .
PID: The number of processes in the system ID Number , It's the only one in the current system .

%CPU:CPU Percentage occupied .
%MEM: Percentage of memory used .
vsz: The amount of virtual memory used by the process (KB).

RSS: The amount of physical memory consumed by the process (KB).
TTY: Indicates which terminal the process is running on . Processes that are not started from the terminal are shown as ?.

Jane said :

pts It's a remote login terminal ctrl+ALT F1-F6 tty1 Image interface 2 and 6
Character interface ? The process executed by the system itself

Open a terminal , This terminal is called pts/0, If you open another terminal , This new terminal is called pts /1.

STAT: The state of the process (D: Non interruptible sleep state :R: Running state ;s : In a dormant state , Can be awakened ;

T: Stop state , It may be suspended in the background or the process is in trace debugging state :
z: Zombie process , The process has been aborted , But some programs are still in memory )
D: System daemons
T: mode 、 Program execution generally stops
R: The program is currently in operation , Or it can be operated ;
s : The program is currently sleeping （ It can be said that idle Status !), But some signals (signal) Wake up the .

T: The program is currently detecting or stopping ;
Z: The program should have terminated , But his father's program can't stop him normally , cause zombie Jiang Zang corpse )
The status of the program

D Non interruptible state ．
They mean the following ::
<: Indicates that the process is running at a high priority

N: Indicates that the process is running at a low priority

L: Indicates that the process has pages locked in memory

s: Indicates that the process is the controlling process
l: Indicates that the process is multithreaded
+: Indicates that the current process is running in the foreground

D: System daemons
T mode 、 Program execution generally stops
START: Time to start the process .|
TIME: The cPU Time .

COMMAND: The name of the command that started the process

2)ps -elf ： The process information in the system will be displayed in long format

-e: Display all process information in the system .
-1: Use long format to display process information .
-f: Display process information in full format .

3.top View dynamic process information

top command ： View dynamic process information

top command - View process dynamic information
In the above output information , The beginning section shows the system tasks (Tasks ) 、CPu Occupy 、 Memory footprint （Mem)、 Swap empty
between （Swap） And so on , Remit . The ranking of the current process is displayed under the general information . The meaning of relevant information is expressed as follows
uptime
13:22:30 current time
up 20days System running time , Indicates that this server is running continuously 20 days

user Number of currently logged in users
load average:0.06,0.60,0.48 System load , That is, the average length of the task queue . The three values are 1 minute 、5 minute 、15 The average from minutes ago to now .

System tasks （Tasks） Information :

total, The total number of processes ;

running, Number of running processes ;

sl Number of dormant processes ;

stopped, Number of processes aborted ;

zombie, The number of dead and unresponsive processes .

CPU Occupancy information :

us, User occupied ;

sy, Kernel occupancy ;

ni, Priority scheduling occupies ;

id, Free cPU;

wa,I/o Waiting for occupation ;

hi, Hardware interrupt occupation ;

si, Software interrupt occupancy ;

st, Virtualization takes up . Learn about the free cPU percentage , It mainly depends on %id part .

Memory footprint (Mem） Information :

total, Total memory space ;free, Free memory ;used, Used memory ;
buff/ cache, The sum of memory and physical buffers .

Swap space (Swap） Occupy :

total, Total swap space ;

free, Free swap space ;

used, Used swap space ;

avail Mem, Available physical space .

4.pgrep Query the process according to specific conditions PID Information

-l: Option to output the corresponding process name and PID
-U： Option to query the processes of a specific user
-t： Option to query the processes running on a specific terminal

5.pstree: List process information in a tree structure

-p： When using this option, you can list the corresponding PID Number
-u： Option to list the corresponding user names
-a： Option to list complete command information

Two , Process startup mode ：

1. Manual start

The front desk starts ： The user enters the command , Direct execution

Background start ： Add... At the end of the command line "&" operator

【jobs -l: View the task list running in the background 】

2. Scheduling start

at command ： Set up a one-time scheduled task

crontab command ： Set up periodic planning tasks

3. Front and back scheduling of processes

ctrl+Z: Suspend the current process , That is to call into the background and stop execution

jobs: View the list of tasks in the background

fg： Restore the background process to the foreground , Task sequence number can be specified

4. Terminate the running of a process

When a user executes a process in the foreground , Can press Ctrl＋C The key combination forces an interrupt （ If the command is not responded for a long time ）.
After interrupting the operation of the foreground process , The system will return to the command line prompt state and wait for the user to enter a new command . When the Ctrl＋C When a key combination cannot terminate a program or needs to end a process running on another terminal or in the background , You can use a special process termination tool kill、killall and pkill.

kill -15 The signal simply tells the corresponding process to proceed " Security 、 Clean exit ", After the program receives the signal , It's usually done before you quit " preparation ", Such as the release of resources 、 Temporary file cleaning and so on , If the preparation is done , And then terminate the program . however , If in " preparation " In the process , Block or other problems cause failure to succeed , Then the application can choose to ignore the termination signal . That's why we sometimes use kill There is no way to order " Kill " Reason for application , Because the default kill The signal is SIGTERM（15）, and SIGTERM（15） Can be blocked and ignored .

Compared with kill -15 command ,kill -9 When executed , There's no time for the app " preparation " Of , So it usually has side effects , Data loss or terminal failure to recover to normal state .