#include "apue.h"#include <sys/wait.h>void pr_exit(int status){    if (WIFEXITED(status))        printf("normal termination, exit status = %d\n",                WEXITSTATUS(status));    else if (WIFSIGNALED(status))        printf("abnormal termination, signal number = %d%s\n",                WTERMSIG(status),#ifdef WCOREDUMP                WCOREDUMP(status) ? " (core file generated)" : "");#else    "");#endif    else if (WIFSTOPPED(status))        printf("child stopped, signal number = %d\n",                WSTOPSIG(status));}

#include "apue.h"#include <sys/wait.h>intmain(void){	pid_t	pid;	int		status;	if ((pid = fork()) < 0)		err_sys("fork error");	else if (pid == 0)				/* child */		exit(7);	if (wait(&status) != pid)		/* wait for child */		err_sys("wait error");	pr_exit(status);				/* and print its status */	if ((pid = fork()) < 0)		err_sys("fork error");	else if (pid == 0)				/* child */		abort();					/* generates SIGABRT */	if (wait(&status) != pid)		/* wait for child */		err_sys("wait error");	pr_exit(status);				/* and print its status */	if ((pid = fork()) < 0)		err_sys("fork error");	else if (pid == 0)				/* child */		status /= 0;				/* divide by 0 generates SIGFPE */	if (wait(&status) != pid)		/* wait for child */		err_sys("wait error");	pr_exit(status);				/* and print its status */	exit(0);}

all: shell1 shell2 fork1 vfork1 wait1shell1: shell1.c	g++ -g -Wall shell1.c ../lib/libapue.a -I ../include -o shell1shell2: shell2.c	g++ -g -Wall shell2.c ../lib/libapue.a -I ../include -o shell2fork1: fork1.c	g++ -g -Wall fork1.c ../lib/libapue.a -I ../include -o fork1vfork1: vfork1.c	g++ -g -Wall vfork1.c ../lib/libapue.a -I ../include -o vfork1wait1: wait1.c	g++ -g -Wall wait1.c ../lib/libapue.a -I ../include -o wait1clean:	rm shell1 shell2 fork1 vfork1 wait1

调用fork两次以避免僵死进程

#include "apue.h"#include <sys/wait.h>int main(void){    printf("file %s, line %d parent, getpid() = %d\n", __FILE__, __LINE__, getpid());    fflush(stdout);    pid_t pid;    if ((pid = fork()) < 0)    {        err_sys("fork error");    }    else if (pid == 0)    { /* first child */        printf("file %s, line %d child 1, getpid() = %d\n", __FILE__, __LINE__, getpid());        fflush(stdout);        if ((pid = fork()) < 0)        {            err_sys("fork error");        }        else if (pid > 0)        {            printf("first child, going to sleep(2)\n");            sleep(2);            printf("first child, after sleep(2), begin exiting\n");            exit(0);   /* parent from second fork == first child */        }        /*         * We‘re the second child; our parent becomes init as soon         * as our real parent calls exit() in the statement above.         * Here‘s where we‘d continue executing, knowing that when         * we‘re done, init will reap our status.         */        printf("file %s, line %d, child 2, getpid() = %d\n", __FILE__, __LINE__, getpid());        printf("second child, going to sleep(5)\n");        sleep(5);        printf("second child, after sleep(5)\n");        printf("second child, parent pid = %d, parent id is 1, which means my parent process is init\n", getppid());        exit(0);    }    if (waitpid(pid, NULL, 0) != pid)  /* wait for first child */        err_sys("waitpid error");    else        printf("after sleep(2), first child exit caught by parent (waitpid)\n");    printf("file %s, line %d, getpid() = %d\n", __FILE__, __LINE__, getpid());    /*     * We‘re the parent (the original process); we continue executing,     * knowing that we‘re not the parent of the second child.     */    exit(0);}

all: shell1 shell2 fork1 vfork1 wait1 fork2shell1: shell1.c	g++ -g -Wall shell1.c ../lib/libapue.a -I ../include -o shell1shell2: shell2.c	g++ -g -Wall shell2.c ../lib/libapue.a -I ../include -o shell2fork1: fork1.c	g++ -g -Wall fork1.c ../lib/libapue.a -I ../include -o fork1fork2: fork2.c	g++ -g -Wall fork2.c ../lib/libapue.a -I ../include -o fork2vfork1: vfork1.c	g++ -g -Wall vfork1.c ../lib/libapue.a -I ../include -o vfork1wait1: wait1.c	g++ -g -Wall wait1.c ../lib/libapue.a -I ../include -o wait1clean:	rm shell1 shell2 fork1 vfork1 wait1 fork2

UNIX环境高级编程8.5exit 8.6wait waitpid