close(2) - NetBSD Manual Pages

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CLOSE(2)                  NetBSD Programmer's Manual                  CLOSE(2)


NAME

     close - delete a descriptor


SYNOPSIS

     #include <unistd.h>

     int
     close(int d);


DESCRIPTION

     The close() system call deletes a descriptor from the per-process object
     reference table.  If this is the last reference to the underlying object,
     the object will be deactivated.  For example, on the last close of a file
     the current seek pointer associated with the file is lost; on the last
     close of a socket(2) associated naming information and queued data are
     discarded; on the last close of a file holding an advisory lock the lock
     is released (see flock(2)).

     When a process exits, all associated descriptors are freed, but since
     there is a limit on active descriptors per processes, the close() system
     call is useful when a large quantity of file descriptors are being han-
     dled.

     When a process calls fork(2), all descriptors for the new child process
     reference the same objects as they did in the parent before the fork().
     If a new process is then to be run using execve(2), the process would
     normally inherit these descriptors.  Most of the descriptors can be rear-
     ranged with dup2(2) or deleted with close() before the execve() is at-
     tempted, but if some of these descriptors will still be needed if the
     execve() fails, it is necessary to arrange for them to be closed only if
     the execve() succeeds.  For this reason, the system call

           fcntl(d, F_SETFD, 1);

     is provided, which arranges that a descriptor ``d'' will be closed after
     a successful execve(); the system call

           fcntl(d, F_SETFD, 0);

     restores the default, which is to not close descriptor ``d''.


RETURN VALUES

     Upon successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and the global integer variable errno is set to indi-
     cate the error.


ERRORS

     close() will fail if:

     [EBADF]       d is not an active descriptor.

     [EINTR]       An interrupt was received.


SEE ALSO

     accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2),
     socketpair(2)


STANDARDS

     The close() function conforms to IEEE Std1003.1-1990 (``POSIX'').

NetBSD 1.4                      April 19, 1994                               1