wait(2)

wait -- wait for child process to stop or terminate

Synopsis

   #include <sys/types.h>
   #include <sys/wait.h>
   
   pid_t wait(int *stat_loc);

Description

wait suspends the calling process until one of its immediate children terminates or until a child that is being traced stops because it has received a signal. The wait system call will return prematurely if a signal is received. If all child processes stopped or terminated prior to the call on wait, return is immediate.

If wait returns because the status of a child process is available, it returns the process ID of the child process. If the calling process had specified a non-zero value for stat_loc, the status of the child process will be stored in the location pointed to by stat_loc. It may be evaluated with the macros described on wstat(5). In the following, status is the object pointed to by stat_loc:

If the child process stopped, the high order 8 bits of status will contain the number of the signal that caused the process to stop and the low order 8 bits will be set equal to WSTOPFLG.
If the child process terminated due to an exit call, the low order 8 bits of status will be 0 and the high order 8 bits will contain the low order 8 bits of the argument that the child process passed to exit. [see exit(2)].
If the child process terminated due to a signal, the high order 8 bits of status will be 0 and the low order 8 bits will contain the number of the signal that caused the termination. In addition, if WCOREFLG is set, a ``core image'' will have been produced. [see signal(2)].

If wait returns because the status of a child process is available, then that status may be evaluated with the macros defined by wstat.

If a parent process terminates without waiting for its child processes to terminate, the parent process ID of each child process is set to 1. This means the initialization process inherits the child processes. [see intro(2)].

Files

Message catalog: uxcore.abi

Return values

If wait returns due to a stopped or terminated child process, the process ID of the child is returned to the calling process. Otherwise, wait returns -1 and sets errno to identify the error.

Errors

In the following conditions, wait fails and sets errno to:

ECHILD: The calling process has no existing unwaited-for child processes.
EINTR: The function was interrupted by a signal.

References

exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2), signal(2), signal(5), waitid(2), waitpid(2), wstat(5)

Notices

See NOTICES in signal(5).

If SIGCLD is held, then wait does not recognize death of children.

Considerations for threads programming

While one thread is blocked, siblings might still be executing.