waitpid(2) SYSTEM CALLS waitpid(2)
NAME
waitpid - wait for child process to change state
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pidt waitpid (pidt pid, int *statloc, int options);
DESCRIPTION
waitpid suspends the calling process until one of its chil-
dren changes state; if a child process changed state prior
to the call to waitpid, return is immediate. pid specifies
a set of child processes for which status is requested.
If pid is equal to (pidt)-1, status is requested for
any child process.
If pid is greater than (pidt)0, it specifies the pro-
cess ID of the child process for which status is
requested.
If pid is equal to (pidt)0 status is requested for any
child process whose process group ID is equal to that
of the calling process.
If pid is less than (pidt)-1, status is requested for
any child process whose process group ID is equal to
the absolute value of pid.
If waitpid returns because the status of a child process is
available, then that status may be evaluated with the macros
defined by wstat(5) . If the calling process had specified a
non-zero value of stat_loc, the status of the child process
will be stored in the location pointed to by stat_loc.
The options argument is constructed from the bitwise
inclusive OR of zero or more of the following flags, defined
in the header file <sys/wait.h>:
WCONTINUED the status of any continued child process
specified by pid, whose status has not been
reported since it continued, shall also be
reported to the calling process.
WNOHANG waitpid will not suspend execution of the
calling process if status is not immediately
available for one of the child processes
specified by pid.
WNOWAIT keep the process whose status is returned in
stat_loc in a waitable state. The process may
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waitpid(2) SYSTEM CALLS waitpid(2)
be waited for again with identical results.
WUNTRACED the status of any child processes specified
by pid that are stopped, and whose status has
not yet been reported since they stopped,
shall also be reported to the calling pro-
cess.
waitpid with options equal to WUNTRACED and pid equal to
(pid_t)-1 is identical to a call to wait(2).
waitpid will fail if one or more of the following is true:
EINTR waitpid was interrupted due to the receipt of
a signal sent by the calling process.
EINVAL An invalid value was specified for options.
ECHILD The process or process group specified by pid
does not exist or is not a child of the cal-
ling process or can never be in the states
specified by options.
SEE ALSO
exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2),
signal(2), sigaction(2), siginfo(5), wstat(5)
DIAGNOSTICS
If waitpid returns because the status of a child process is
available, this function shall return a value equal to the
process ID of the child process for which status is
reported. If waitpid returns due to the delivery of a sig-
nal to the calling process, a value of -1 shall be returned
and errno shall be set to EINTR. If this function was
invoked with WNOHANG set in options, it has at least one
child process specified by pid for which status is not
available, and status is not available for any process
specified by pid, a value of 0 shall be returned. Other-
wise, a value of -1 shall be returned, and errno shall be
set to indicate the error.
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