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



PROLOG
       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
       close — close a file descriptor

SYNOPSIS
       #include <unistd.h>

       int close(int fildes);

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

ERRORS
       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
   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
       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
       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
       None.

SEE ALSO
       Section 2.6, STREAMS, exec, fattach(), fclose(), fdetach(), fopen(),
       ioctl(), open(), unlink()

       The Base Definitions volume of POSIX.1‐2008, <unistd.h>

COPYRIGHT
       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(3POSIX)