Linux and UNIX Man Pages

Test Your Knowledge in Computers #76
Difficulty: Easy
Richard Stallman's GNU project was also started in response to AT&T's increasingly restrictive Unix software licensing terms.
True or False?
Linux & Unix Commands - Search Man Pages

wait(2) [hpux man page]

wait(2) 							System Calls Manual							   wait(2)

NAME
wait(), waitpid() - wait for child process to stop or terminate SYNOPSIS
DESCIPTION
The and functions obtain status information pertaining to one of the caller's child processes. Various options permit status information to be obtained for child processes that have terminated or stopped. If status information is available for two or more child processes, the order in which their status is reported is unspecified. The function suspends execution of the calling thread until status information for one of the terminated child processes of the calling process is available, or until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process. If more than one thread is suspended in or awaiting termination of the same process, exactly one thread returns the process sta- tus at the time of the target process termination. If status information is available prior to the call to return is immediate. The function is equivalent to if the pid argument is and the options argument is 0. Otherwise, its behavior is modified by the values of the pid and options arguments. Note that if the parent process terminates without waiting for its child processes to terminate, these processes are adopted by and recog- nize the initialization process as their parent. The pid argument specifies the child processes for which status is requested. The function only returns the status of a child process from this set: o If pid is equal to status is requested for any child process. In this respect, is equivalent to o If pid is greater than 0, it specifies the process ID of a single child process for which status is requested. o If pid is 0, status is requested for any child process whose process group ID is equal to that of the calling process. o If pid is less than status is requested for any child process whose process group ID is equal to the absolute value of pid. The stat_loc argument is the address where status of the specified child processes is placed. The options argument is constructed from the bitwise-inclusive OR of zero or more of the following flags defined in the header file. The function reports the status of any continued child process specified by pid whose status has not been reported since it continued from a job control stop. The function does not suspend execution of the calling thread if status is not immediately available for one of the child processes specified by pid. HP-UX EXTENSION: Keep the process whose status is returned in stat_loc in a waitable state. The process may be waited for again with identical results, provided the state of the process doesn't change in the interim. The status of any child processes specified by pid that are stopped, and whose status has not yet been reported since they stopped, is also reported to the requesting process. HP-UX EXTENSION: If and only if this flag is set, or (see wait3(2)) returns information on child or attached processes that are stopped because they received a or signal, and whose status has not yet been reported. Regardless of this flag, status is returned for child or attached processes that have terminated or are stopped and traced and whose sta- tus has not yet been reported. If the calling process has the signal action set or has set to and the process has no unwaited-for children that were transformed into zom- bie processes, the calling thread blocks until all of the children of the process containing the calling thread terminate, and and fail and set to If or return because the status of a child process is available, these functions return a value equal to the process ID of the child process. In this case, if the value of the argument stat_loc is not a null pointer, information is stored in the location pointed to by stat_loc. The value stored at the location pointed to by stat_loc is 0 if and only if the status returned is from a terminated child process that terminated by one of the following means: 1. The process returned 0 from main(). 2. The process called _exit() or exit() with a status argument of 0. 3. The process was terminated because the last thread in the process terminated. Previous versions of HP-UX documented the bit encodings of the status returned by which could be interpreted directly and applications doing this will continue to work correctly. However, new applications should use the provided status interpretation macros shown below for maximum portability. Status Interpretation Macros Regardless of its value, this information may be interpreted using the following macros, which are defined in and evaluate to integral expressions; the stat_val argument is the integer value pointed to by stat_loc. HP-UX EXTENSION: If the value of is nonzero, this macro evaluates to a nonzero value if a "core image" dump was produced (see signal(5)). If the value of is nonzero, this macro evaluates to the low-order 8 bits of the status argument that the child process passed to or or the value the child process returned from Evaluates to a nonzero value if status was returned for a child process that has continued from a job control stop. Evaluates to a nonzero value if status was reported for a child process that terminated normally. Evaluates to a nonzero value if status was reported for a child process that terminated due to the receipt of a signal that was not caught (see Evaluates to a nonzero value if status was reported for a child process that is currently stopped. If the value of is nonzero, this macro evaluates to the number of the signal that caused the child process to stop. If the value of is nonzero, this macro evaluates to the number of the signal that caused the termination of the child process. If the information pointed to by stat_loc was stored by a call to that specified the flag and did not specify the flag, exactly one of the macros and evaluates to a nonzero value. If the information pointed to by stat_loc was stored by a call to that specified the and flags, exactly one of the macros and evaluates to a nonzero value. If the information pointed to by stat_loc was stored by a call to that did not specify the or flags, or by a call to the wait() function, exactly one of the macros and evaluates to a nonzero value. If the information pointed to by stat_loc was stored by a call to that did not specify the flag and specified the lag, or by a call to the wait() function, exactly one of the macros and evaluates to a nonzero value. There may be additional implementation-dependent circumstances under which and report status. This does not occur unless the calling process or one of its child processes explicitly makes use of a nonstandard extension. In these cases the interpretation of the reported status is implementation-defined. If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are assigned a new parent process ID corresponding to an implementation-defined system process. In earlier versions of HP-UX, the status interpretation macros and have the same definitions as the correspondingly named macros in BSD 4.3 and earlier systems, so existing applications that depend on these definitions will continue to work correctly. However, if the applica- tion is recompiled, the feature test macro must be turned on so that the old definitions of these macros override the new definitions of these macros that are in effect by default. The only difference between the old and new definitions is the argument typing. Type union is used in the BSD definitions while type int is used in the default definitions. RETURN VALUE
If or returns because the status of a child process is available, these functions return a value equal to the process ID of the child process for which status is reported. If or returns due to the delivery of a signal to the calling process, is returned and is set to If was invoked with 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, 0 is returned. Otherwise, is returned, and is set to indicate the error. ERRORS
If the call fails, is set to one of the following values: The calling process has no existing unwaited-for child processes. The stat_loc argument points to an illegal address or problems were encountered in the reporting of the status information for the specified child process. Note that the reliable detection of this error is implementation-dependent. The function was interrupted by a signal. The value of the location pointed to by stat_loc argument is undefined. If the call fails, is set to one of the following values: The process specified by pid does not exist or is not a child of the calling process, or the process group specified by pid does not exist or does not have any member process that is a child of the calling process. The stat_loc argument points to an illegal address or problems were encountered in the reporting of the status information for the specified child process. Note that the reliable detection of this error is implementation-dependent. The was interrupted by a signal. The value of the location pointed to by stat_loc is undefined. The options argument is not valid. WARNINGS
HP-UX EXTENSION: The operation of is affected if the signal is set to (see the section of signal(5)). Signal handlers that cause system calls to be restarted can affect the condition (see bsdproc(3C) and sigaction(2)). APPLICATION USAGE
Threads Considerations In a multithreaded application, only the calling thread is suspended by call. and will not return until all threads in the process have reached the desired state. For example, the calls will not return until all threads have terminated. If the or options are specified for the call, it will not return until all threads have stopped or continued, respectively. SEE ALSO
Exit conditions in sh(1), exec(2), exit(2), fork(2), pause(2), ttrace(2), wait3(2), waitid(2), signal(5), AUTHOR
and were developed by HP, AT&T and the University of California, Berkeley. STANDARDS CONFORMANCE
wait(2)

Featured Tech Videos