WAITID(2)WAITID(2)NAMEwaitid - wait for child process to change state
int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
The waitid() function suspends the calling process until one of its
child processes changes state. It records the current state of a child
in the structure pointed to by infop. It returns immediately if a child
process changed state prior to the call.
The idtype and id arguments specify which children waitid() is to
wait for, as follows:
o If idtype is P_PID, waitid() waits for the child with a
process ID equal to (pid_t)id.
o If idtype is P_PGID, waitid() waits for any child with a
process group ID equal to (pid_t)id.
o If idtype is P_ALL, waitid() waits for any child and id is
The options argument is used to specify which state changes waitid() is
to wait for. It is formed by bitwise OR operation of any of the follow‐
Return the status for any child that was stopped and has
Wait for process(es) to exit.
Keep the process in a waitable state.
Wait for and return the process status of any child that
has stopped upon receipt of a signal.
Wait for traced process(es) to become trapped or reach a
breakpoint (see ptrace(3C)).
The infop argument must point to a siginfo_t structure, as defined in
siginfo.h(3HEAD). If waitid() returns because a child process was found
that satisfies the conditions indicated by the arguments idtype and
options, then the structure pointed to by infop will be filled by the
system with the status of the process. The si_signo member will always
be equal to SIGCHLD.
One instance of a SIGCHLD signal is queued for each child process whose
status has changed. If waitid() returns because the status of a child
process is available and WNOWAIT was not specified in options, any
pending SIGCHLD signal associated with the process ID of that child
process is discarded. Any other pending SIGCHLD signals remain pending.
If waitid() returns due to a change of state of one of its children and
WNOHANG was not used, 0 is returned. Otherwise, −1 is returned and
errno is set to indicate the error. If WNOHANG was used, 0 can be
returned (indicating no error); however, no children may have changed
state if info->si_pid is 0.
The waitid() function will fail if:
The set of processes specified by idtype and id does not con‐
tain any unwaited processes.
The infop argument points to an illegal address.
The waitid() function was interrupted due to the receipt of a
signal by the calling process.
An invalid value was specified for options, or idtype and id
specify an invalid set of processes.
With options equal to WEXITED | WTRAPPED, waitid() is equivalent to
waitpid(3C). With idtype equal to P_ALL and options equal to WEXITED |
WTRAPPED, waitid() is equivalent to wait(3C).
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Standard │
│MT-Level │ Async-Signal-Safe │
SEE ALSOIntro(2), exec(2), exit(2), fork(2), pause(2), sigaction(2),
ptrace(3C), signal(3C), siginfo.h(3HEAD), wait(3C), waitpid(3C),
Jun 9, 2004 WAITID(2)