Process and planned task management

Program : Binary , static state /bin/date,/usr/sbin/sshd

process : It's the process of running the program , dynamic , It has life cycle and operation state .

1、 The relationship between program and process

Program

• Save on hard disk 、 Executable code and data in media such as CD
• Code stored statically in a file

process

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

 

2、 Planning task management crontab2-1

crontab command

• According to the preset time period （ minute 、 Hours 、 God .......） Repeat the user specified command operation
• It belongs to periodic plan
• Main settings file         

• Global profile , Located in file ：/etc/crontab
• System default location , Located in the directory ：/etc/cron.*/
• User defined settings , Located in file ：/var/spool/cron/ user name

3、 Planning task management crontab2-2

management crontab Planning tasks

• Edit scheduled task

crontab -e [ user name ]

• View scheduled tasks

crontab -l [-u user name ]

• Delete scheduled task

crontab -r [-u user name ]

 4、crontab The format of task configuration 2-1

 

 

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

 5、crontab The format of task configuration 2-2

  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

Application example

• 0 17 * * 1-5       Monday to Friday... Every day 17:00
• 30 8 * * 1,3,5     Every Monday 、 3、 ... and 、 Five 8 spot 30 branch
• 0 8-18/2  *  * *     8 Point to 18 Between every point 2 Hours
• 0 *  */3  * *            Every time 3 God

6、 Thread state

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

2. Can run (RUNABLE): After the thread object is created , Other threads ( such as main Threads ） Called the object's start() Method . The thread in this state is in the runnable 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 refers to the thread giving up for some reason cpu Right to use , That is to say, to give up cputimeslice, Stop running temporarily . Until the thread becomes runnable (runnable) state , To have another chance to get cpu timeslice Go to run (running) state . There are three types of obstruction :   

• Waiting for a jam : function (running) Thread execution of o.wait() Method ,JVw The thread will be put into the waiting queue (waitting queue) in .
•   Synchronous blocking : function (runing) When the thread of gets the synchronization lock of the object , If the synchronization lock is held by another thread , be JVWM The thread will be put into the lock pool (lockpool) in . 
•   Other blockages : function (running) Thread execution of Thread.sleep (longms) or t.join() Method , Or send out 1/o When asked ,Jvw 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 regenerated

7、ps Command to view static process statistics

TTY ： terminal

Common parameters

• -a: Display all process information under the current terminal , Include other users' processes . And "x" When the options are combined, all process information in the system will be displayed .
• -u: Output process information in user oriented format .
• -x: Display the process information of the current user under all terminals .

  Common option combinations

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

 

  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 ?. 

STAT: The state of the process (D: Non interruptible sleep state :R: Running state ;s: In a dormant state , Can be awakened ; Four : 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 、 The execution of the program generally stops
• R: The program is currently in operation , Or the town is 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

8、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 space (Swap) And so on , The following shows the ranking of the current process

• System tasks (Tasks） Information : total, The total number of processes ;running, Number of running processes ;sleeping, 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/0, 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 Men, Available physical space .
• %CPU   Last updated to now CPU Percentage of time used
• %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

 

 

top Command full screen operation interface shortcut key :
Default 3s Refresh once , Press s Modify the refresh time, press space : Refresh now .

• P: Press cPU Sort
• M: Sort by memory T: Sort by time
• p: Process worker e, View the status of a process N Key according to the start time to sort the number keys 1: Show the... For each kernel cPU Usage rate
• u/Uu: Specify the user to display
• h: You can get top Online help information for the program q: Jian can exit normally top Program

notes : If through top The ranking tool finds a process cPT The occupancy rate is very high , The process needs to be terminated , Can be in top Press... In the operation interface k key , Then... Will appear at the top of the list "PID to signal/kill [default pid =3180]:" A reminder of , Enter... Of the specified process according to the prompt PID Sign and press Enter key , appear "send pid 5597signal [15/sigterm]" Prompt information for secondary confirmation of , Then press Enter Press OK to terminate the corresponding process .