02-19-2002
try running this code...
#include <unistd.h>
void main()
{
int f;
printf("\n Parent procces ID=%d\n",getpid());
f=fork();
if(f==0)
{
printf("\n Child process ID=%d father=%d\n",getpid(),getppid());
}
else
{
wait(0);
}
exit(0);
}
Here's the output:
./a.out
Parent procces ID=27711
Child process ID=27712 father=27711
The problem in the previous code is that the parent does not wait for the termination of the child process....Hence sometimes the parent process dies before the child ..Hence the init process(pid=1) becomes the parent of the child process...
By adding wait() or waitpid() we ensure that the parent waits for the termination of the child...
Pls. correct me if I am wrong....!!!
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WAIT(2) System Calls Manual WAIT(2)
NAME
wait - wait for process to terminate
SYNOPSIS
wait(status)
int *status;
wait(0)
DESCRIPTION
Wait causes its caller to delay until a signal is received or one of its child processes terminates. If any child has died since the last
wait, return is immediate; if there are no children, return is immediate with the error bit set (resp. with a value of -1 returned). The
normal return yields the process ID of the terminated child. In the case of several children several wait calls are needed to learn of all
the deaths.
If (int)status is nonzero, the high byte of the word pointed to receives the low byte of the argument of exit when the child terminated.
The low byte receives the termination status of the process. See signal(2) for a list of termination statuses (signals); 0 status indi-
cates normal termination. A special status (0177) is returned for a stopped process which has not terminated and can be restarted. See
ptrace(2). If the 0200 bit of the termination status is set, a core image of the process was produced by the system.
If the parent process terminates without waiting on its children, the initialization process (process ID = 1) inherits the children.
SEE ALSO
exit(2), fork(2), signal(2)
DIAGNOSTICS
Returns -1 if there are no children not previously waited for.
ASSEMBLER
(wait = 7.)
sys wait
(process ID in r0)
(status in r1)
The high byte of the status is the low byte of r0 in the child at termination.
WAIT(2)