NAME

wait − wait for child process to stop or terminate

SYNOPSIS

int wait (stat_loc)
int ∗stat_loc;

DESCRIPTION

wait suspends the calling process until 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 returns 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 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 and if the child process 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 contain the number of the signal that caused the process to stop and the low order 8 bits are set equal to 0177. 

If the child process terminated due to an exit call, the low order 8 bits of status are zero and the high order 8 bits 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 are zero and the low order 8 bits contain the number of the signal that caused the termination. In addition, if the low order seventh bit (i.e., bit 200) is set, a “core image” is 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 intro(2)].

wait fails and returns immediately in the following case:

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

SEE ALSO

exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2), signal(2). 

WARNING

wait fails and its actions are undefined if stat_loc points to an invalid address. 

See WARNING in signal(2).

DIAGNOSTICS

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. 

March 13, 1992