关于孤儿进程和僵尸进程的实践
首先关于孤儿进程
processA processB processC
ps -ef|grep process
sroot 9665 24982 0 23:42 pts/0 00:00:00 /bin/bash ./processA.sh
sroot 9666 9665 023:42 pts/0 00:00:00 /bin/bash./processB.sh
sroot 9667 9666 023:42 pts/0 00:00:00 /bin/bash./processC.sh
24982 -> 9665 /processA.sh ->9666 ./processB.sh ->9667 ./processC.sh
24982是INIT下/bin/bash .
[[email protected] 24982]# pwd
/proc/24982
[[email protected] 24982]# ll
total 0
lrwxrwxrwx. 1 sroot root 0 Jun 22 23:45 cwd -> /home/craft/shell
-r--------. 1 sroot root 0 Jun 22 23:45 environ
lrwxrwxrwx. 1 sroot root 0 Jun 22 23:32 exe -> /bin/bash
[[email protected] 24982]# ps -ef |grep 24982
sroot 9665 24982 0 23:42 pts/0 00:00:00 /bin/bash ./processA.sh
sroot 19995 2740 023:47 pts/1 00:00:00 grep 24982
sroot 24982 24935 0 23:32 pts/0 00:00:00 bash
之后，kill -9 processB 看A和C的变化
[[email protected] 24982]# ps aux |grep process
sroot 17693 0.0 0.0 106104 1172 pts/0 S+ 00:22 0:00 /bin/bash./processA.sh
sroot 17694 0.0 0.0 106104 1172 pts/0 S+ 00:22 0:00 /bin/bash./processB.sh
sroot 17695 32.8 0.0 106108 1192 pts/0 S+ 00:22 0:01 /bin/bash ./processC.sh
ps aux |grep process
只剩下一个/processC.sh，A和B 都不见了
sroot 17695 36.2 0.0 106108 1192 pts/0 R 00:22 0:12 /bin/bash ./processC.sh
也就是B死掉的时候，会去通知他的父进程A。
本身A的存在就是等待B 完成的，所以B死掉，A也释放了。
但是C并不知道。
这个时候A不停的继续跑，并且无法用ctrl+c结束。
知道kill -9 processC的进程号。
这个时候并不会产生僵尸进程
此时，C就是孤儿进程。
如何产生僵尸进程
首先，僵尸进程是由于父进程没有回收子进程。
父进程会使用wait函数来等待子进程若子进程结束，用这个函数来回收子进程。
#include <stdio.h>
#include <sys/types.h>
#include <time.h>
int main()
{
//fork a child process
pid_t pid = fork(); 产生一个子进程。新产生的子进程同样用这个代码。这样就会有两个程序在使用同一个代码运行。
if (pid > 0) //parentprocess父进程进入这个if判断。
{
printf("in parentprocess, sleep for one miniute...zZ...\n");
struct timeval tv;
gettimeofday(&tv,NULL);
printf("parent microsecond:%ld\n",tv.tv_sec*1000000 +tv.tv_usec); //微秒 输出当前的时间
sleep(60);
printf("aftersleeping, and exit!\n");
gettimeofday(&tv,NULL);
printf("parentmicrosecond after sleeping:%ld\n",tv.tv_sec*1000000 + tv.tv_usec); //微秒
重新输出sleep之后的时间
}
else if (pid == 0) 子进程进入这个if判断语句
{
//child process exit,and to be a zombie process
printf("in child process, and exit!\n");
structtimeval tv;
gettimeofday(&tv,NULL);
printf("child microsecond:%ld\n",tv.tv_sec*1000000 +tv.tv_usec); //微秒
输出进入到子进程的时间
}
}
用gcc指令编译
[[email protected] test]# gcc zombie1.c -o zombie1
[[email protected] test]# ./zombie1 运行
运行结果如下
./zombie1
in parent process, sleep for one miniute...zZ...父进程先进入第一个判断语句，输出时间
parent microsecond:1498469853526179
in child process, and exit! 子进程进入判断语句，输出时间
child microsecond:1498469853526404
after sleeping, and exit!
parent microsecond aftersleeping:1498469913532272 父进程结束sleep，输出时间，这个时间跟第一个输出时间相差为60s。
用ps查看进程情况
[[email protected] test]# ps aux |grep zombie
root 3445 0.0 0.0 3924 416 pts/2 S+ 05:37 0:00 ./zombie1
root 3446 0.0 0.0 0 0 pts/2 Z+ 05:37 0:00 [zombie1]<defunct>
出现一个僵尸进程
[[email protected] test]# ps -ef |grep zomb
root 3445 3024 0 05:37 pts/2 00:00:00./zombie1
root 3446 3445 0 05:37 pts/2 00:00:00 [zombie1] <defunct>
从进程ID能看出这个僵尸进程是zombie的子进程
改进程序，来更好的观察由于父进程是否调用wait带来的结果。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main()
{
int i = 0;
char cCmd = 'a';
char cTmp = 'a';
printf("process start with pid: %d\n", getpid());
pid_t pid = fork();
switch (pid)
{
case 0:
{
printf("child_process start with pid: %d\n", getpid());
printf("child_process exit\n");
exit(1);
}
break;
case -1:
break;
default:
{
while (1)
{
printf("Input 'q' to exit without recycle the resource of child and will generate zombile process.\n");
printf("Input 'Q' to recyle resource of child.\n");
printf("No matter q or Q , the parent process will exit .\n");
cCmd = getchar();
while ((cTmp = getchar()) != '\n');
if (cCmd == 'q')
{
printf(" exit without recycle the resource of child ,generate zombile process.Please use ps command to check\n");
break;
}
else if (cCmd == 'Q')
{
printf(" Parent process will recycle the child resource .wait child_process to exit\n");
wait(NULL);
printf("Child process was recycled ,the zombile process was clear.press any key to continue...\n");
cTmp = getchar();
while ((cTmp = getchar()) != '\n');
break;
}
else
{
printf("You input %c. can not be recognized by this program Please reinput\n", cCmd);
}
}
}
break;
}
printf("Parent_process exit\n");
return 0;
}
设置了判断语句让用户输入，在子进程结束的时候，产生僵尸进程。
若用户输入q,则调用wait函数回收该僵尸进程父进程再退出。
若用户输入Q，则不调用wait函数回收，直接退出。
[[email protected] fish]# ./zombile
process start with pid: 23216
Input 'q' to exit without recycle the resource of child and will generate zombil
Input 'Q' to recyle resource of child.
No matter q or Q , the parent process will exit .
child_process start with pid: 23217
child_process exit
此时查看进程发现产生了僵尸进程
[[email protected] ~]# ps -ef |grep zombile
root 23216 22233 0 17:34 pts/1 00:00:00 ./zombile
root 23217 23216 0 17:34 pts/1 00:00:00 [zombile] <defunct>
root 23223 22391 0 17:34 pts/2 00:00:00 grep zombile
Q
Parent process will recycle the child resource .wait child_process to exit
Child process was recycled ,the zombile process was clear.press any key to continue...
运行该程序发现，在使用wait之后，僵尸子进程就消失了。
[[email protected] ~]# ps -ef |grep zombile
root 23216 22233 0 17:34 pts/1 00:00:00 ./zombile
root 23225 22391 0 17:34 pts/2 00:00:00 grep zombile
只剩下父进程自己。
此时如果直接退出该程序，退出父进程，子进程也会跟着消失，可见，清除父进程是清楚僵尸子进程的方法之一。
kill掉defunct进程方法有二：
1，重启服务器电脑，这个是最简单，最易用的方法，但是如果你服务器电脑上运行有其他的程序，那么这个方法，代价很大。
所以，尽量使用下面一种方法2，找到该defunct僵尸进程的父进程，将该进程的父进程杀掉，则此defunct进程将自动消失。
转载于:https://blog.51cto.com/12833256/1941834