Process Creation fork, Getpid, Getppid

Create a process:

/* ******************* * Function: Create a new process by copying the current process (as with the parent process) and performing the same position *pid_t: generally 16-bit signed integer number, not enough to typedef     * Return value: 0: " In the parent process,---> Return child process Number *         0: In child process---> return 0 *        -1: Failed and set errno * *************** */pid_t Fork (void);

Parent-Child process difference:Fork return value is not the same

Different PID

Ppid different

Pending signals (unresponsive signals) and file locks do not inherit

Resource Utilization 0

Init process: Is the ancestor process of all processes---process No. 1th

Eg: simple creation of a child process

/************************ * Create a child process ***********************/#include<stdio.h>#include<stdlib.h>#include<unistd.h>intMain () {pid_t pid; printf ("[%d]:begin\n", Getpid ());  //0. Be sure to flush the previously opened stream fflush (NULL) before fork; //1. Create a processPID =Fork (); if(PID <0) {perror ("Fork ()"); Exit (1); }    //2. Sub-process    if(PID = =0) {printf ("[%d]:child is working\n", Getpid ()); }    Else{printf ("[%d]:p arent is working\n", Getpid ()); } printf ("[%d]:end\n", Getpid ()); Exit (0);}

There are two kinds of results without fflus.

Result 1:

[root]#./forkbase
[3862]:begin
[3862]:p arent is working
[3862]:end
[3863]:child is working
[3863]:end

Result 2:

[root]#./forkbase >/tmp/out
[root]# Cat/tmp/out
[3997]:begin
[3997]:p arent is working
[3997]:end
[3997]:begin
[3998]:child is working
[3998]:end

*[root]#./forkbase output to terminal (row buffer, add \ n to flush buffer, so begin prints once)

*[root]#./forkbase >/tmp/out Redirect to a file, the file is in full buffer mode (\ n is just a newline), because the child process inherits everything from the parent process, then the buffer has two begin, so begin will be printed 2 times,

*: Scheduler scheduling policy to determine which process runs first

Get PID Number:

#include <sys/types.h><unistd.h>/******** get current process PID number ********* / pid_t getpid (void); /* ******* Gets the parent process PID number of the current process ******** */ pid_t getppid (void);

=======================================================================

Man PS

Command PS: Some information about the output process

PS AXF: Information about the printing process PID TTY STAT time COMMAND

Process number occupies terminal state consumption time which command triggered the

PS AXM: More information view

PS ax-l : View LWP (Lightweight process)---threads in a Linux-specific way

=======================================================================

Process number is used down

Process Creation fork, Getpid, Getppid