NAME

wait − wait for child process to stop or terminate

SYNOPSIS

int wait (stat_loc)
int ∗stat_loc;

int wait ((int ∗)0)

HP-UX COMPATIBILITY

Level: HP-UX/RUN ONLY

Origin: System V

DESCRIPTION

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

If stat_loc (taken as an integer) is non-zero, 16 bits of information called status are stored in the low order 16 bits of the location pointed to by stat_loc. Status can be used to differentiate between stopped and terminated child processes.  If the child process is terminated, status identifies the cause of termination and passes useful information to the parent. This is accomplished in the following manner:

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 0177. 

If the child process terminated due to an exit or _exit call, the low order 8 bits of status will be zero 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 zero and the low order 8 bits will contain the number of the signal that caused the termination. In addition, if the low order seventh bit (i.e., bit 0200) is set, a "core image" will have been produced; see signal(2).

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 glossary(9).

Wait will fail if one or more of the following are true:

­[ECHILD] The calling process has no existing unwaited-for child processes.  In this case, wait returns immediately. 

­[EFAULT] Stat_loc points to an illegal address. 

NOTE

The behavior of wait is affected by setting the SIGCLD signal to SIG_IGN.  See Special Signals section of signal(2)fordetails.

RETURN VALUE

If wait returns due to the receipt of a signal, a value of −1 is returned to the calling process and errno is set to EINTR.  If wait returns due to a stopped or terminated child process, 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. 

SEE ALSO

Exit conditions ($?) in sh(1), exec(2), exit(2), fork(2), pause(2), ptrace(2), signal(2). 

Hewlett-Packard  —  last mod. May 11, 2021