Working with the Unix OS

Processes II
A process that terminates cannot leave the system until its parent accept code. If its parent is already dead, it is
adopted by the "init" process
If a process's parent is alive but never executes a wait() the process's will never be accepted and the process will
remain a zombie.
/* zombie.c */
#include
main()
{
int pid;
pid = fork(); /* duplicate process */
if (pid != 0) /* parent lives */
{
while (1)
sleep(1000); /* child dies */
}
else {
exit(2);
}
}
ps
PID TT STAT TIME COMMAND
160 p1 S 0:00 -ksh
170 p1 S 0:00 zombie # parent process
171 p1 Z 0:00
180 p1 R 0:00 ps
kill 170
[1] Terminated
ps
PID TT STAT TIME COMMAND
160 p1 S 0:00 -ksh
190 p1 R 0:00 ps
/* wait.c */
#include
main()
{
int pid, status, childpid;
printf("original process with PID %d\n", getpid());
pid = fork(); /* duplicate process */
if (pid != 0)
{ /* parent */
printf("parent process with PID %d and PPID %d\n", getpid(), getppid());
childpid = wait(&status); /* wait for child */
printf("child PID %d terminated with exit code %d\n", childpid, status>>8);
} else { /* child */
printf("child process with PID %d and PPID %d\n", getpid(), getppid());
exit(2);
}
printf("PID %d terminates\n", getpid());
}
original process with PID 190
child process with PID 191 and PPID 190
parent process with PID 190 and PPID 188
child PID 191 terminated with exit code 2
PID 191 terminates
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