4.3BSD-UWisc/man/cat2/wait.2

WAIT(2)             UNIX Programmer's Manual              WAIT(2)



NAME
     wait, wait3 - wait for process to terminate

SYNOPSIS
     #include <sys/wait.h>

     pid = wait(status)
     int pid;
     union wait *status;

     pid = wait(0)
     int pid;

     #include <sys/time.h>
     #include <sys/resource.h>

     pid = wait3(status, options, rusage)
     int pid;
     union wait *status;
     int options;
     struct rusage *rusage;

DESCRIPTION
     _W_a_i_t 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 _w_a_i_t, return is immediate, returning the
     process id and exit status of one of the terminated chil-
     dren.  If there are no children, return is immediate with
     the value -1 returned.

     On return from a successful _w_a_i_t call, _s_t_a_t_u_s is nonzero,
     and the high byte of _s_t_a_t_u_s contains the low byte of the
     argument to _e_x_i_t supplied by the child process; the low byte
     of _s_t_a_t_u_s contains the termination status of the process.  A
     more precise definition of the _s_t_a_t_u_s word is given in
     <_s_y_s/_w_a_i_t._h>.

     _W_a_i_t_3 provides an alternate interface for programs that must
     not block when collecting the status of child processes.
     The _s_t_a_t_u_s parameter is defined as above.  The _o_p_t_i_o_n_s
     parameter is used to indicate the call should not block if
     there are no processes that wish to report status (WNOHANG),
     and/or that children of the current process that are stopped
     due to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal should
     also have their status reported (WUNTRACED).  If _r_u_s_a_g_e is
     non-zero, a summary of the resources used by the terminated
     process and all its children is returned (this information
     is currently not available for stopped processes).

     When the WNOHANG option is specified and no processes wish
     to report status, _w_a_i_t_3 returns a _p_i_d of 0.  The WNOHANG and
     WUNTRACED options may be combined by _o_r'ing the two values.



Printed 12/27/86          June 30, 1985                         1






WAIT(2)             UNIX Programmer's Manual              WAIT(2)



NOTES
     See _s_i_g_v_e_c(2) for a list of termination statuses (signals);
     0 status indicates normal termination.  A special status
     (0177) is returned for a stopped process that has not ter-
     minated and can be restarted; see _p_t_r_a_c_e(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) inher-
     its the children.

     _W_a_i_t and _w_a_i_t_3 are automatically restarted when a process
     receives a signal while awaiting termination of a child pro-
     cess.

RETURN VALUE
     If _w_a_i_t returns due to a stopped or terminated child pro-
     cess, the process ID of the child is returned to the calling
     process.  Otherwise, a value of -1 is returned and _e_r_r_n_o is
     set to indicate the error.

     _W_a_i_t_3 returns -1 if there are no children not previously
     waited for;  0 is returned if WNOHANG is specified and there
     are no stopped or exited children.

ERRORS
     _W_a_i_t will fail and return immediately if one or more of the
     following are true:

     [ECHILD]       The calling process has no existing
                    unwaited-for child processes.

     [EFAULT]       The _s_t_a_t_u_s or _r_u_s_a_g_e arguments point to an
                    illegal address.

SEE ALSO
     exit(2)

















Printed 12/27/86          June 30, 1985                         2