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



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult 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 out-
       standing  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  sig-
       nals, 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 opera-
       tion  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 oper-
       ation may be canceled upon close(), is implementation-defined.

       If a shared memory object or a memory mapped file 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 shared memory object or a memory mapped file 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 valid 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.

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 IEEE Std 1003.1-2001 only intends to permit such behavior by specifying
       the [EINTR] error condition.

FUTURE DIRECTIONS
       None.

SEE ALSO
       STREAMS, fattach(), fclose(), fdetach(), fopen(), ioctl(), open(), the Base Definitions volume  of  IEEE Std 1003.1-2001,
       <unistd.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     CLOSE(3P)