Unix/Linux Go Back    


Linux 2.6 - man page for close (linux section 3posix)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


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

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 deallo-
       cate 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  imme-
       diately.

       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 mes-
       sage 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 can-
       celed 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 implemen-
       tation-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 orig-
       inal  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 cor-
       responding fclose() routine rather than close().  Once a file is closed, the file descrip-
       tor 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 Defini-
       tions 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, Copyright (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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					 CLOSE(P)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 09:47 AM.