PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

CLOSE(3P)                 POSIX Programmer's Manual                CLOSE(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       close — close a file descriptor

SYNOPSIS         top

       #include <unistd.h>

       int close(int fildes);

DESCRIPTION         top

       The close() function shall deallocate the file descriptor indicated
       by fildes.  To deallocate means to make the file descriptor available
       for return by subsequent calls to open() or other functions that
       allocate file descriptors. All outstanding record locks owned by the
       process on the file associated with the file descriptor shall be
       removed (that is, unlocked).

       If close() is interrupted by a signal that is to be caught, it shall
       return −1 with errno set to [EINTR] and the state of fildes is
       unspecified. If an I/O error occurred while reading from or writing
       to the file system during close(), it may return −1 with errno set to
       [EIO]; if this error is returned, the state of fildes is unspecified.

       When all file descriptors associated with a pipe or FIFO special file
       are closed, any data remaining in the pipe or FIFO shall be
       discarded.

       When all file descriptors associated with an open file description
       have been closed, the open file description shall be freed.

       If the link count of the file is 0, when all file descriptors
       associated with the file are closed, the space occupied by the file
       shall be freed and the file shall no longer be accessible.

       If a STREAMS-based fildes is closed and the calling process was
       previously registered to receive a SIGPOLL signal for events
       associated with that STREAM, the calling process shall be
       unregistered for events associated with the STREAM. The last close()
       for a STREAM shall cause the STREAM associated with fildes to be
       dismantled. If O_NONBLOCK is not set and there have been no signals
       posted for the STREAM, and if there is data on the module's write
       queue, close() shall wait for an unspecified time (for each module
       and driver) for any output to drain before dismantling the STREAM.
       The time delay can be changed via an I_SETCLTIME ioctl() request. If
       the O_NONBLOCK flag is set, or if there are any pending signals,
       close() shall not wait for output to drain, and shall dismantle the
       STREAM immediately.

       If the implementation supports STREAMS-based pipes, and fildes is
       associated with one end of a pipe, the last close() shall cause a
       hangup to occur on the other end of the pipe. In addition, if the
       other end of the pipe has been named by fattach(), then the last
       close() shall force the named end to be detached by fdetach().  If
       the named end has no open file descriptors associated with it and
       gets detached, the STREAM associated with that end shall also be
       dismantled.

       If fildes refers to the master side of a pseudo-terminal, and this is
       the last close, a SIGHUP signal shall be sent to the controlling
       process, if any, for which the slave side of the pseudo-terminal is
       the controlling terminal. It is unspecified whether closing the
       master side of the pseudo-terminal flushes all queued input and
       output.

       If fildes refers to the slave side of a STREAMS-based pseudo-
       terminal, a zero-length message may be sent to the master.

       When there is an outstanding cancelable asynchronous I/O operation
       against fildes when close() is called, that I/O operation may be
       canceled. An I/O operation that is not canceled completes as if the
       close() operation had not yet occurred. All operations that are not
       canceled shall complete as if the close() blocked until the
       operations completed. The close() operation itself need not block
       awaiting such I/O completion. Whether any I/O operation is canceled,
       and which I/O operation may be canceled upon close(), is
       implementation-defined.

       If a memory mapped file or a shared memory object remains referenced
       at the last close (that is, a process has it mapped), then the entire
       contents of the memory object shall persist until the memory object
       becomes unreferenced.  If this is the last close of a memory mapped
       file or a shared memory object and the close results in the memory
       object becoming unreferenced, and the memory object has been
       unlinked, then the memory object shall be removed.

       If fildes refers to a socket, close() shall cause the socket to be
       destroyed. If the socket is in connection-mode, and the SO_LINGER
       option is set for the socket with non-zero linger time, and the
       socket has untransmitted data, then close() shall block for up to the
       current linger interval until all data is transmitted.

RETURN VALUE         top

       Upon successful completion, 0 shall be returned; otherwise, −1 shall
       be returned and errno set to indicate the error.

ERRORS         top

       The close() function shall fail if:

       EBADF  The fildes argument is not a open file descriptor.

       EINTR  The close() function was interrupted by a signal.

       The close() function may fail if:

       EIO    An I/O error occurred while reading from or writing to the
              file system.

       The following sections are informative.

EXAMPLES         top

   Reassigning a File Descriptor
       The following example closes the file descriptor associated with
       standard output for the current process, re-assigns standard output
       to a new file descriptor, and closes the original file descriptor to
       clean up. This example assumes that the file descriptor 0 (which is
       the descriptor for standard input) is not closed.

           #include <unistd.h>
           ...
           int pfd;
           ...
           close(1);
           dup(pfd);
           close(pfd);
           ...

       Incidentally, this is exactly what could be achieved using:

           dup2(pfd, 1);
           close(pfd);

   Closing a File Descriptor
       In the following example, close() is used to close a file descriptor
       after an unsuccessful attempt is made to associate that file
       descriptor with a stream.

           #include <stdio.h>
           #include <unistd.h>
           #include <stdlib.h>

           #define LOCKFILE "/etc/ptmp"
           ...
           int pfd;
           FILE *fpfd;
           ...
           if ((fpfd = fdopen (pfd, "w")) == NULL) {
               close(pfd);
               unlink(LOCKFILE);
               exit(1);
           }
           ...

APPLICATION USAGE         top

       An application that had used the stdio routine fopen() to open a file
       should use the corresponding fclose() routine rather than close().
       Once a file is closed, the file descriptor no longer exists, since
       the integer corresponding to it no longer refers to a file.

       Implementations may use file descriptors that must be inherited into
       child processes for the child process to remain conforming, such as
       for message catalog or tracing purposes. Therefore, an application
       that calls close() on an arbitrary integer risks non-conforming
       behavior, and close() can only portably be used on file descriptor
       values that the application has obtained through explicit actions, as
       well as the three file descriptors corresponding to the standard file
       streams. In multi-threaded parent applications, the practice of
       calling close() in a loop after fork() and before an exec call in
       order to avoid a race condition of leaking an unintended file
       descriptor into a child process, is therefore unsafe, and the race
       should instead be combatted by opening all file descriptors with the
       FD_CLOEXEC bit set unless the file descriptor is intended to be
       inherited across exec.

RATIONALE         top

       The use of interruptible device close routines should be discouraged
       to avoid problems with the implicit closes of file descriptors by
       exec and exit().  This volume of POSIX.1‐2008 only intends to permit
       such behavior by specifying the [EINTR] error condition.

       Note that the requirement for close() on a socket to block for up to
       the current linger interval is not conditional on the O_NONBLOCK
       setting.

       The standard developers rejected a proposal to add closefrom() to the
       standard. Because the standard permits implementations to use
       inherited file descriptors as a means of providing a conforming
       environment for the child process, it is not possible to standardize
       an interface that closes arbitrary file descriptors above a certain
       value while still guaranteeing a conforming environment.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.6, STREAMS, exec(1p), fattach(3p), fclose(3p), fdetach(3p),
       fopen(3p), ioctl(3p), open(3p), unlink(3p)

       The Base Definitions volume of POSIX.1‐2008, unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                           CLOSE(3P)