Process and planned task management

Catalog

One , The relationship between program and process

1, Thread state

2, The difference between process and multithreading

  Two , Check the process

1, View process static information ：ps

  Explanation of terms

2, ps -elf

  Explanation of terms

3、 ... and , Zombie process

4, View process dynamic information ：top

 1, Process dynamic information

2, Process information area noun explanation

4,top Common commands

5, View process information ：pgrep

 6, View the process tree ：pstree

 7,& and job

 kill command  

  Four , Planning task management

1, Plan tasks at once ：at

 2, Periodic task setup ：crontab

  Task configuration format

---

One , The relationship between program and process

Program

• Save on hard disk , Executable code and data in media such as optical disc
• Code stored statically in a file

process

• stay CPU And the program code running in memory
• Dynamically executed code
• Father child process
• Each program can create one or more processes

1, Thread state

1, newly build （NEW）： A new thread object is created

2, Can run （RUNNABLE）; After the thread object is created , Other threads （ such as main Threads ） Called the object's start（ Method ）. Threads in this state can only run in the thread pool , Waiting to be selected by thread scheduling , obtain cpu Right to use

3, function （RUNNING）; Operational state （runnable） The thread of the cpu Time slice （timeslice） Execute program code .

4, Blocking （BLOCKED）： Blocking state means that the thread has given up for some reason cpu Right to use , It also gives way cpu timelise Go to run （running） state . There are three types of congestion ：

（ One ） Waiting for a jam ： The running thread executes o.wait Method ,JVM Will put the changed thread into the waiting queue .

（ Two ） Synchronous blocking ： Running 1 The thread is getting the synchronization lock time of the object , If the synchronization lock is occupied by other threads , be JVM Will put the changed thread into the lock pool .

（ 3、 ... and ） Insufficient system resources ） function (running) Thread execution of Thread.sleep (longms)ms) or t. join() Method , Or send out I/o When asked ,JVM It puts the thread in a blocking state . When sleep() Status timeout 、join() Wait for the thread to terminate or timeout 、 perhaps I/o When it's done , The thread goes back to runnable (runnable) state .
5, Death （DEAD） Threads run()、main() Method execution ends , Or quit because of an exception run() Method , The thread ends its life cycle . Dead threads cannot be reborn

2, The difference between process and multithreading

  Process is the basic unit of operating system resource allocation , Thread is the basic unit of task investigation and execution . Processes without threads can be treated as single threads , If there are multiple threads in a process , The execution process is not a line , It is accomplished by multiple lines , Threads are part of the process , So threads are also called lightweight processes or lightweight processes

  Two , Check the process

1, View process static information ：ps

Method 1 ：ps aux

a	Display all processes on the terminal , Include other users' processes
u	Represents the user who lists the processes
x	Display the process of all terminals

  Explanation of terms

USER	Users of the process
PID	Process ID
%CPU	Process occupied cpu percentage
%MEM	Percentage of memory used
VSZ	The amount of virtual memory used by the process
RSS	The amount of physical memory consumed by the process
TTY	The terminal name of the startup process , Processes that are not started from the terminal are displayed as
STAT	D： Non interruptible sleep state ;R： Running state ;S： In a dormant state , Can be awakened ;T： Stop state , It could be a pause in the background or the process is tracking Debug status ;Z： Zombie process , The process has been aborted , But some programs are still in memory
START	The time the process was triggered to start
TIME	The process actually uses CPU Running time
COMMAND	The start command of the process

2, ps -elf

  Explanation of terms

F	The system token that the kernel assigns to a process
S	State of process
UID	The user who started these processes
PID	Process of process ID
PPID	The process number of the parent process （ If the process is started by another process ）
C	In the life cycle of a process CPU utilization
PRI	Priority of the process （ The higher the number, the lower the priority ）
NI	Humility value is used to participate in determining priority
ADDR	The memory address of the process /td>
SZ	If the process is swapped out , The approximate size of the swap space required
WCHAN	If the process is sleeping , The system function name in sleep is displayed
STIME	System time when the process started
TTY	The terminal device when the process starts
TIME	The cumulative amount required to run the process CPU Time
CMD	The start command of the process

3、 ... and , Zombie process

A process is over , But if the parent process of the process has ended , Then the process will not become a zombie process , Because every process ends 1 When , The system will scan the current system running 1 So the process , See if that process is a child process that just ended , If so , Just from init To take over it , Become its parent process , After the subprocess exits init It will recycle the relevant resources it occupies .

But when the child process ends before the parent process , The parent process does not recycle the child process , Release the resources occupied by the subprocess , At this point, the subprocess will become a zombie process .

4, View process dynamic information ：top

 1, Process dynamic information

first line ： Task queue information

19:29:21	system time
up 10:20	The system has been running for a long time
1 user	Number of currently logged in users
load average:0.03,0.02,0.05	System load , That is, the number of tasks processed by the system per unit time , The last three values are 1 minute ,5 minute ,15 The average from minutes ago to now

The second line ： Process information

tasks	The total number of processes
running	Number of running processes
sleeping	Number of dormant processes
stopped	Number of processes terminated
zombie	The number of dead processes

The third line ：CPU Information

us	User occupied
sy	Kernel occupancy
ni	Priority scheduling occupies
id	Free CPU（ To understand leisure CPU percentage . It mainly depends on %id part ）
wa	l/o Waiting for occupation
hi	Hardware interrupt occupation
si	Software interrupt occupancy
st	Virtualization takes up

In the fourth row ： Memory information

total	Total memory space
free	Free memory
used	Used memory
buff/cache	The total buffer of physical memory and interactive memory

The fifth row ： Exchange space information

total	Total swap space
free	Free swap space
used	Used swap space
avail    Mem	Available physical space

2, Process information area noun explanation

PID	process ID
USER	Process users
PR	priority
NI	Humility value , Negative value indicates high priority , A positive value indicates a low priority
VIRT	The size of virtual memory used by the process , Company kb
RES	The amount of physical memory used by the process , Company kb
SHR	Shared memory size , Company kb
S	Process status
%CPU	Last updated to now CPU Percentage occupied
%MEM	Percentage of physical memory used by the process
TIME	Used by process CPU Total time , Company 1/100 second
COMMAND	Command name / Command line

4,top Common commands

P	according to CPU Sort by percentage size
M	Sort by resident memory size
N	Sort by start time
c	Toggle display command name and full command line
h	You can get top Online help information for the program
k	Enter... Of the specified process according to the prompt PID Sign and press Enter Key to terminate the corresponding process
q	sign out top Program
Numbers 1	Show CPU Number and state

5, View process information ：pgrep

 6, View the process tree ：pstree

 7,& and job

&： Indicates that the current process is suspended without output

 jobs -l ： View tasks in the background

 bc command ： You can resume the specified tasks suspended in the background

fg command ： You can put the background tasks on the front desk

 kill command  

  Four , Planning task management

1, Plan tasks at once ：at

 

 2, Periodic task setup ：crontab

Edit scheduled task

crontab -e [-u user name ]

View scheduled tasks

crontab   -l [-u user name ]

Delete task plan

crontab -r [-u user name ]

   Every three minutes , Automatically view the time and mount the disk partition table , And output the result to /opt/kk.txt

  Task configuration format

Field	explain
minute	The value is 0~59 Any integer between
Hours	The value is 0~23 Any integer between
date	The value is 1~31 Any integer between
month	The value is 1~12 Any integer between
week	The value is 0~7 Any integer between ,0 or 7 On behalf of Sunday
command	Command or program script to execute

	Special representation of time value
*	This is an arbitrary range of time
,	Represents multiple discontinuous time points of an interval
-	Represents a continuous time range
/	Specify the time and frequency of the interval