.TH WAITPID 2
.UC 4
.SH NAME
waitpid \- wait for a given pid
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.B int waitpid (pid_t pid, unsigned long *stat_addr, int options);
.fi
.SH DESCRIPTION
.B waitpid()
waits for 
.I pid
as specified in 
.I options.
.PP
Alowable options are:
.br
.B WUNTRACED 
- set when we want to be notified of successful exit of 
.I pid
.br
.B WNOHANG
- set if we don't want to wait around for a long time.
.PP
.B waitpid()
will exit when :
.nf
1.  The waited for process terminates or enters a ZOMBIE state.
2.  An unblocked signal, or SIGCHLD is caught.
3.  An error condition occurs.
.fi
.PP
.I stat_addr is non NULL,  then unless     
.B WUNTRACED 
is set and the status of    
.I pid
is not
.B TASKSTOPPED
then 
.I *stat_addr
will be set to the exit code of  
.I pid.
.PP
.B waitpid()
will return one of the following : 
.br
.nf
1.  pid if the process terminates.
2.  0 if we told it to not hang, and the process hasn't terminated.
3.  A negative value indicating an error.
.fi 
.SH ERRORS
.B -ERESTARTSYS
is returned if 
.B WNOHANG
was not set, when an unblocked signal or SGICHLD was caught.
.PP
.B -ECHILD
is returned if the child process didn't exist,
or WUNTRACED was unclear and there was no exit code.
.SH FILES
linux/kernel/signal.c
.br
/usr/include/linux/sys.h
.br
/usr/include/unistd.h
.SH SEE ALSO
wait(3)