1CLOSE(3P)                  POSIX Programmer's Manual                 CLOSE(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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11

NAME

13       close — close a file descriptor
14

SYNOPSIS

16       #include <unistd.h>
17
18       int close(int fildes);
19

DESCRIPTION

21       The close() function shall deallocate the file descriptor indicated  by
22       fildes.   To deallocate means to make the file descriptor available for
23       return by subsequent calls to open() or other functions  that  allocate
24       file  descriptors. All outstanding record locks owned by the process on
25       the file associated with the file descriptor shall be removed (that is,
26       unlocked).
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28       If  close()  is  interrupted by a signal that is to be caught, it shall
29       return −1 with errno set to [EINTR] and the state of fildes is unspeci‐
30       fied.  If  an  I/O  error occurred while reading from or writing to the
31       file system during close(), it may return −1 with errno set  to  [EIO];
32       if this error is returned, the state of fildes is unspecified.
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34       When  all  file descriptors associated with a pipe or FIFO special file
35       are closed, any data remaining in the pipe or FIFO shall be discarded.
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37       When all file descriptors associated with an open file description have
38       been closed, the open file description shall be freed.
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40       If  the  link count of the file is 0, when all file descriptors associ‐
41       ated with the file are closed, the space occupied by the file shall  be
42       freed and the file shall no longer be accessible.
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44       If  a STREAMS-based fildes is closed and the calling process was previ‐
45       ously registered to receive a SIGPOLL signal for events associated with
46       that STREAM, the calling process shall be unregistered for events asso‐
47       ciated with the STREAM. The last close() for a STREAM shall  cause  the
48       STREAM  associated  with  fildes to be dismantled. If O_NONBLOCK is not
49       set and there have been no signals posted for the STREAM, and if  there
50       is data on the module's write queue, close() shall wait for an unspeci‐
51       fied time (for each module and driver) for any output to  drain  before
52       dismantling  the  STREAM.  The  time delay can be changed via an I_SET‐
53       CLTIME ioctl() request. If the O_NONBLOCK flag is set, or if there  are
54       any  pending  signals,  close() shall not wait for output to drain, and
55       shall dismantle the STREAM immediately.
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57       If the implementation supports STREAMS-based pipes, and fildes is asso‐
58       ciated with one end of a pipe, the last close() shall cause a hangup to
59       occur on the other end of the pipe. In addition, if the  other  end  of
60       the pipe has been named by fattach(), then the last close() shall force
61       the named end to be detached by fdetach().  If the  named  end  has  no
62       open  file descriptors associated with it and gets detached, the STREAM
63       associated with that end shall also be dismantled.
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65       If fildes refers to the master side of a pseudo-terminal, and  this  is
66       the  last  close,  a  SIGHUP  signal  shall  be sent to the controlling
67       process, if any, for which the slave side of the pseudo-terminal is the
68       controlling terminal. It is unspecified whether closing the master side
69       of the pseudo-terminal flushes all queued input and output.
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71       If fildes refers to the slave side of a STREAMS-based  pseudo-terminal,
72       a zero-length message may be sent to the master.
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74       When  there  is  an  outstanding  cancelable asynchronous I/O operation
75       against fildes when close() is called, that I/O operation may  be  can‐
76       celed.  An  I/O  operation  that  is  not  canceled completes as if the
77       close() operation had not yet occurred. All  operations  that  are  not
78       canceled  shall complete as if the close() blocked until the operations
79       completed. The close() operation itself need not  block  awaiting  such
80       I/O  completion.  Whether  any I/O operation is canceled, and which I/O
81       operation may be canceled upon close(), is implementation-defined.
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83       If a memory mapped file or a shared memory object remains referenced at
84       the last close (that is, a process has it mapped), then the entire con‐
85       tents of the memory  object  shall  persist  until  the  memory  object
86       becomes  unreferenced.   If  this  is the last close of a memory mapped
87       file or a shared memory object and the  close  results  in  the  memory
88       object  becoming unreferenced, and the memory object has been unlinked,
89       then the memory object shall be removed.
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91       If fildes refers to a socket, close() shall  cause  the  socket  to  be
92       destroyed.  If  the  socket  is  in  connection-mode, and the SO_LINGER
93       option is set for the socket with non-zero linger time, and the  socket
94       has  untransmitted data, then close() shall block for up to the current
95       linger interval until all data is transmitted.
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RETURN VALUE

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

102       The close() function shall fail if:
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104       EBADF  The fildes argument is not a open file descriptor.
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106       EINTR  The close() function was interrupted by a signal.
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108       The close() function may fail if:
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110       EIO    An  I/O error occurred while reading from or writing to the file
111              system.
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113       The following sections are informative.
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EXAMPLES

116   Reassigning a File Descriptor
117       The following example closes the file descriptor associated with  stan‐
118       dard  output  for  the current process, re-assigns standard output to a
119       new file descriptor, and closes the original file descriptor  to  clean
120       up.  This  example  assumes  that  the  file descriptor 0 (which is the
121       descriptor for standard input) is not closed.
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123           #include <unistd.h>
124           ...
125           int pfd;
126           ...
127           close(1);
128           dup(pfd);
129           close(pfd);
130           ...
131
132       Incidentally, this is exactly what could be achieved using:
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134           dup2(pfd, 1);
135           close(pfd);
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137   Closing a File Descriptor
138       In the following example, close() is used to close  a  file  descriptor
139       after an unsuccessful attempt is made to associate that file descriptor
140       with a stream.
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142           #include <stdio.h>
143           #include <unistd.h>
144           #include <stdlib.h>
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146           #define LOCKFILE "/etc/ptmp"
147           ...
148           int pfd;
149           FILE *fpfd;
150           ...
151           if ((fpfd = fdopen (pfd, "w")) == NULL) {
152               close(pfd);
153               unlink(LOCKFILE);
154               exit(1);
155           }
156           ...
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APPLICATION USAGE

159       An application that had used the stdio routine fopen() to open  a  file
160       should  use  the  corresponding  fclose()  routine rather than close().
161       Once a file is closed, the file descriptor no longer exists, since  the
162       integer corresponding to it no longer refers to a file.
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164       Implementations  may  use  file descriptors that must be inherited into
165       child processes for the child process to remain conforming, such as for
166       message  catalog  or  tracing  purposes. Therefore, an application that
167       calls close() on an arbitrary integer  risks  non-conforming  behavior,
168       and  close()  can  only portably be used on file descriptor values that
169       the application has obtained through explicit actions, as well  as  the
170       three  file  descriptors corresponding to the standard file streams. In
171       multi-threaded parent applications, the practice of calling close()  in
172       a  loop  after  fork() and before an exec call in order to avoid a race
173       condition of  leaking  an  unintended  file  descriptor  into  a  child
174       process,  is therefore unsafe, and the race should instead be combatted
175       by opening all file descriptors with the FD_CLOEXEC bit set unless  the
176       file descriptor is intended to be inherited across exec.
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RATIONALE

179       The use of interruptible device close routines should be discouraged to
180       avoid problems with the implicit closes of file descriptors by exec and
181       exit().  This volume of POSIX.1‐2008 only intends to permit such behav‐
182       ior by specifying the [EINTR] error condition.
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184       Note that the requirement for close() on a socket to block  for  up  to
185       the  current  linger interval is not conditional on the O_NONBLOCK set‐
186       ting.
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188       The standard developers rejected a proposal to add closefrom()  to  the
189       standard. Because the standard permits implementations to use inherited
190       file descriptors as a means of providing a conforming  environment  for
191       the  child process, it is not possible to standardize an interface that
192       closes arbitrary file descriptors above a  certain  value  while  still
193       guaranteeing a conforming environment.
194

FUTURE DIRECTIONS

196       None.
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SEE ALSO

199       Section  2.6,  STREAMS,  exec, fattach(), fclose(), fdetach(), fopen(),
200       ioctl(), open(), unlink()
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202       The Base Definitions volume of POSIX.1‐2008, <unistd.h>
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205       Portions of this text are reprinted and reproduced in  electronic  form
206       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
207       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
208       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
209       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
210       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
211       event of any discrepancy between this version and the original IEEE and
212       The  Open Group Standard, the original IEEE and The Open Group Standard
213       is the referee document. The original Standard can be  obtained  online
214       at http://www.unix.org/online.html .
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216       Any  typographical  or  formatting  errors that appear in this page are
217       most likely to have been introduced during the conversion of the source
218       files  to  man page format. To report such errors, see https://www.ker
219       nel.org/doc/man-pages/reporting_bugs.html .
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223IEEE/The Open Group                  2013                            CLOSE(3P)
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