WAIT(2)

NAME
wait, waitpid - wait for process termination

SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>

pid_t wait(int *status)
pid_t waitpid(pid_t pid, int *status, int options);

DESCRIPTION
The wait function suspends execution of the current process until a child has exited, or until a signal is delivered whose action is to terminate the current process or to call a signal handling function. If a child has already exited by the time of the call (a so-called "zombie" process), the function returns immediately. Any system resources used by the child are freed. The waitpid function function suspends execution of the current process until a child as specified by the pid argument has exited, or until a signal is deliverd whose action is to terminate the current process or to call a signal handling function. If a child as requested by pid has already exited by the time of the call (a so-called "zombie" process), the function returns immediately. Any system resources used by the child are freed. The value of pid can be one of:

< -1
    which means to wait for any child process whose process group ID is equal to the absolute value of

-1  which means to wait for any child process whose process group ID is equal to the absolute value of pid.

-1  which means to wait for any child process; this is the same behaviour which wait exhibits.

0   which means to wait for any child process whose process group ID is equal to that of the calling process.

> 0 which means to wait for the child whose process ID is equal to the value of pid.

The value of options is an exclusive OR of zero or more of the following constants:

WNOHANG
    which means to return immediately if no child is there to be waited for.

WUNTRACED
    which means to also return for children which are stopped, and whose status has not been reported.

If status is not NULL, wait or waitpid store status information in the location pointed to by statloc. This status can be evaluated with the following macros:

WIFEXIDED(*status)
    is non -zero if the child exited normally.

WEXITSTATUS(*status)
    evaluates to the least significant eight bits of the return code of the child which terminated, which may have been set as the argument to a call to exit() or as the argument for a return statement in the main program. This macro can only be evaluated if WIFEXITED returned non-zero.

WIFSIGNALED(*status)
    returns true if the child process exited because of a signal which was not caught.

WTERMSIG(*status)
    returns the number of the signal that caused the child process to terminate. This macro can only be evaluated if WIFSIGNALED returned non-zero.

WIFSTOPPED(*status)
    returns true if the child process which caused the return is currently stopped; this is only possible if the call was done using WUNTRACED.

WSTOPSIG(*status)
    returns the number of the signal which caused the child to stop. This macro can only be evaluated if WIFSTOPPED returned non-zero.

RETURN VALUE
The process ID of the child which exited, -1 on error or zero if WNOHANG was used and no child was available (in which case, errno is set to an appropriate value).

ERRORS

ECHILD
    if the child process specified in pid does not exist.

EPERM
    if the effective userid of the calling process does not match that of the process being waited for, and the effective userid of the calling process it not that of the superuser.

ERESTARTSYS
    if WNOHANG was not set and an unblocked signal or a SIGCHLD was caught; this is an extension to the POSIX.1 standard.

CONFORMS TO
POSIX.1

SEE ALSO
signal(2), wait4(2), signal(7)