Processes, jobs, and services

process 、 Homework

1、PID： Process ID ( Each new process has a unique PID)
2、PPID： Parent process ID
3、 Any process can create a child process
4、 stay redhat 7 above , The parent of all processes : systemd, stay redhat 5. 6 in , The parent of all processes : init

• process

process ：LInux Independent programs that run on their own

Interactive process ： By a shell Qi Dynamic process , It can be run in the foreground , It can also run in the background

Batch process ： It's a sequence of processes , No contact with the terminal

Monitor progress ( Daemon ) ：Linux When the system starts , The process started , And run it in the background

• Homework

Homework ： An executing process , And jobs can contain one or more processes .

Operation control ： Control the behavior of running processes . Such as : Suspend a process 、 It will be implemented later 、 interrupt , In this way, users can switch between multiple jobs

• View live processes top

top 

 Parameters 
-d： Number of seconds , Appoint top The command is updated every few seconds . The default is 3 second 

 stay top Commands that can be executed in command interaction mode :
~? or h： Display help for interactive mode 
P： With CPU Usage sort , This is the default 
M： Sort by memory usage 
N： With PID Sort 
q： sign out top

• View the process tree pstree

pstree

 Parameters 
-p： Show progress PID
-u： Show users of the process 

• . Look at the processes running in the background

jobs
// View the current background process status 

jobs -l： In addition to listing the process number , Also list PID
jobs -r： List processes that only run in the background 
jobs -S： List processes that are only suspended in the background 

ps -aux： List all processes and states 
ps -ef： List all processes 
ps -l： List the processes and states related to the current user 
ps -u： user name ： View the process status of a user 
ps -j： List PID \ SPID 	

Parameter interpretation ps -aux Inquire about

1、%CPU： The amount of CPU Usage rate 
2、%MEM： Occupied memory usage ,
3、VSZ： Occupied by the virtual memory size 
4、RSS： Occupied by memory size 
5、TTY： The secondary device number of the terminal (minor device numberoftty)
6、STAT： The state trip 
7、START  Start Time travel 
8、TIME： Execution time 
9、COMMAND： Instruction executed 

START Process status

 Running :
R： The process is running or waiting to run 

 sleep :
S： Sleeping but can be awakened 
D： Sleeping , And cannot be awakened , The process was interrupted , May cause abnormal state of the equipment 
K： Sleeping , And cannot be awakened , The process can be interrupted .
 Has stopped :
T： The process was stopped , But it can be restored through other processes 
T： The process being debugged 

 Stiff stop :
Z： The child process signals the parent process when it exits , except PID Outside , All resources are released 
X： The parent process gets the structure of the child process , Child processes can be released completely , This state is not visible in the process 

START Priority of process status

<： High priority 
n： Low priority 
s： Include subprocesses 
+： Process groups in the background 

• interrupt 、 Kill process

The signal ： Pass to Linux Process operation

kill-l PID ： The display can be passed to Linux All signals of the process 

ctrl +c ： Interrupt process 
ctrl +z ：  Suspend process 

kill -9 PID ： Force to kill a process 
kill -15 PID ： Terminate a process in the normal way 

• Control command of operation

&： Use this symbol after the command , Commands can be executed in the background

fg + Job number ： Transfer the background command to the foreground to continue execution , Can't put it back in the background
bg + Job number ： Continue the command suspended in the background

Control services and daemons

ssh： It's an agreement

sshd： It's a process

systemd： Is the parent of all processes (Linux kernel 3.0 Above version )

systemctl： Users manage various types of systemd object , These objects are called : unit

Common units :：.service ( Service unit ) .socket ( Socket ) .path ( Path unit )

systemctl start sshd

start： Start in the system - - Item service 
stop： Wait for the procedure to be processed before stop,
restart： The direct closing program is on 
reload： Reload the configuration file , Process halted , Then load the configuration file , Continue with follow-up . Process PID No change 
enable： Set power on self start 
disable： Turn off and start automatically 
status： View the status of a unit 

• systemctl status sshd.service Query parameters

loaded: Unit configuration file to handle 
active (running) : Running 
active (exited) : Configuration is successful 
active
(waiting) : Running , But waiting for events 
inactive: It's not running 
enable: Boot up 
disabled: Power on does not start automatically 
static: Can't start , But it can be started by a unit that has been started