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WAIT(2) UNIX Programmer's Manual WAIT(2) NAME wait, waitpid, wait4, wait3 - wait for process terminatation SYNOPSIS #include <sys/types.h> #include <sys/wait.h> pid = wait(status) int pid; union wait *status; #include <sys/time.h> #include <sys/resource.h> pid = waitpid(wpid, status, options); int pid; int wpid; union wait *status; int options; pid = wait3(status, options, rusage); int pid; union wait *status; int options; struct rusage *rusage; pid = wait4(wpid, status, options, rusage); int pid; int wpid; union wait *status; int options; struct rusage *rusage; DESCRIPTION The wait function suspends execution of its calling process until status information is available for a terminated child process, or a signal is received. On return from a success- ful wait call, the status area contains termination informa- tion about the process that exited as defined below. The wait4 call provides a more general interface for pro- grams that need to wait for certain child processes, that need resource utilization statistics accummulated by child processes, or that require options. The other wait func- tions are implemented using wait4 . The wpid parameter specifies the set of child processes for which to wait. If wpid is -1, the call waits for any child process. If wpid is 0, the call waits for any child process in the process group of the caller. If wpid is greater than zero, the call waits for the process with process id wpid . If wpid is less than -1, the call waits for any process Printed 11/26/99 March 12, 1993 1 WAIT(2) UNIX Programmer's Manual WAIT(2) whose process group id equals the absolute value of wpid . The status parameter is defined below. The options parame- ter contains the bitwise OR of any of the following options. The WNOHANG option is used to indicate that the call should not block if there are no processes that wish to report status. If the WUNTRACED option is set, children of the current process that are stopped due to a SIGTTIN , SIGTTOU , SIGTSTP , or SIGSTOP signal also have their status reported. If rusage 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, wait4 returns a process id of 0. The waitpid call is identical to wait4 with an rusage value of zero. The older wait3 call is the same as wait4 with a wpid value of -1. The following macros may be used to test the manner of exit of the process. One of the first three macros will evaluate to a non-zero (true) value: WIFEXITED(status) - True if the process terminated normally by a call to _exit(2) or exit(2) . WIFSIGNALED(status) - True if the process terminated due to receipt of a signal. WIFSTOPPED(status) - True if the process has not terminated, but has stopped and can be restarted. This macro can be true only if the wait call specified the WUNTRACED option or if the child process is being traced (see ptrace(2)). Depending on the values of those macros, the following mac- ros produce the remaining status information about the child process: WEXITSTATUS(status) - If WIFEXITED(status) is true, evalu- ates to the low-order 8 bits of the argument passed to _exit(2) or exit(2) by the child. WTERMSIG(status) - If WIFSIGNALED(status) is true, evaluates to the number of the signal that caused the termination of the process. WCOREDUMP(status) If WIFSIGNALED(status) is true, evaluates as true if the termination of the process was accompanied by Printed 11/26/99 March 12, 1993 2 WAIT(2) UNIX Programmer's Manual WAIT(2) the creation of a core file containing an image of the pro- cess when the signal was received. WSTOPSIG(status) If WIFSTOPPED(status) is true, evaluates to the number of the signal that caused the process to stop. NOTES See sigvec(2) for a list of termination signals. A status of 0 indicates normal termination. If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are assigned the parent process 1 ID (the init process ID). If a signal is caught while any of the wait calls is pend- ing, the call may be interrupted or restarted when the signal-catching routine returns, depending on the options in effect for the signal; see intro(2), System call restart. RETURN VALUES If wait() 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 errno is set to indicate the error. If wait4(), wait3() or waitpid() returns due to a stopped or terminated child process, the process ID of the child is returned to the calling process. If there are no children not previously awaited, -1 is returned with errno set to [ECHILD]. Otherwise, if WNOHANG is specified and there are no stopped or exited children, 0 is returned. If an error is detected or a caught signal aborts the call, a value of -1 is returned and errno is set to indicate the error. ERRORS Wait() will fail and return immediately if: [ECHILD] The calling process has no existing unwaited-for child processes. [EFAULT] The status or rusage arguments point to an illegal address. (May not be detected before exit of a child process.) [EINTR] The call was interrupted by a caught signal, or the signal had the SV_INTERRUPT flag set. STANDARDS The wait and waitpid functions are defined by POSIX; wait4 and wait3 are not specified by POSIX. The WCOREDUMP macro and the ability to restart a pending wait call are Printed 11/26/99 March 12, 1993 3 WAIT(2) UNIX Programmer's Manual WAIT(2) extensions to the POSIX interface. SEE ALSO exit(2) , sigvec(2) A wait function call appeared in Version 6 AT&T UNIX. Printed 11/26/99 March 12, 1993 4
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