1CLOSE(P) POSIX Programmer's Manual CLOSE(P)
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6 close - close a file descriptor
7
9 #include <unistd.h>
10 int close(int fildes);
12
15 The close() function shall deallocate the file descriptor indicated by
16 fildes. To deallocate means to make the file descriptor available for
17 return by subsequent calls to open() or other functions that allocate
18 file descriptors. All outstanding record locks owned by the process on
19 the file associated with the file descriptor shall be removed (that is,
20 unlocked).
21 If close() is interrupted by a signal that is to be caught, it shall
23 return -1 with errno set to [EINTR] and the state of fildes is unspeci‐
24 fied. If an I/O error occurred while reading from or writing to the
25 file system during close(), it may return -1 with errno set to [EIO];
26 if this error is returned, the state of fildes is unspecified.
27 When all file descriptors associated with a pipe or FIFO special file
29 are closed, any data remaining in the pipe or FIFO shall be discarded.
30 When all file descriptors associated with an open file description have
32 been closed, the open file description shall be freed.
33 If the link count of the file is 0, when all file descriptors associ‐
35 ated with the file are closed, the space occupied by the file shall be
36 freed and the file shall no longer be accessible.
37 If a STREAMS-based fildes is closed and the calling process was previ‐
39 ously registered to receive a SIGPOLL signal for events associated with
40 that STREAM, the calling process shall be unregistered for events asso‐
41 ciated with the STREAM. The last close() for a STREAM shall cause the
42 STREAM associated with fildes to be dismantled. If O_NONBLOCK is not
43 set and there have been no signals posted for the STREAM, and if there
44 is data on the module's write queue, close() shall wait for an unspeci‐
45 fied time (for each module and driver) for any output to drain before
46 dismantling the STREAM. The time delay can be changed via an I_SET‐
47 CLTIME ioctl() request. If the O_NONBLOCK flag is set, or if there are
48 any pending signals, close() shall not wait for output to drain, and
49 shall dismantle the STREAM immediately.
50 If the implementation supports STREAMS-based pipes, and fildes is asso‐
52 ciated with one end of a pipe, the last close() shall cause a hangup to
53 occur on the other end of the pipe. In addition, if the other end of
54 the pipe has been named by fattach(), then the last close() shall force
55 the named end to be detached by fdetach(). If the named end has no open
56 file descriptors associated with it and gets detached, the STREAM asso‐
57 ciated with that end shall also be dismantled.
58 If fildes refers to the master side of a pseudo-terminal, and this is
60 the last close, a SIGHUP signal shall be sent to the controlling
61 process, if any, for which the slave side of the pseudo-terminal is the
62 controlling terminal. It is unspecified whether closing the master side
63 of the pseudo-terminal flushes all queued input and output.
64 If fildes refers to the slave side of a STREAMS-based pseudo-terminal,
66 a zero-length message may be sent to the master.
67 When there is an outstanding cancelable asynchronous I/O operation
69 against fildes when close() is called, that I/O operation may be can‐
70 celed. An I/O operation that is not canceled completes as if the
71 close() operation had not yet occurred. All operations that are not
72 canceled shall complete as if the close() blocked until the operations
73 completed. The close() operation itself need not block awaiting such
74 I/O completion. Whether any I/O operation is canceled, and which I/O
75 operation may be canceled upon close(), is implementation-defined.
76 If a shared memory object or a memory mapped file remains referenced at
78 the last close (that is, a process has it mapped), then the entire con‐
79 tents of the memory object shall persist until the memory object
80 becomes unreferenced. If this is the last close of a shared memory
81 object or a memory mapped file and the close results in the memory
82 object becoming unreferenced, and the memory object has been unlinked,
83 then the memory object shall be removed.
84 If fildes refers to a socket, close() shall cause the socket to be
86 destroyed. If the socket is in connection-mode, and the SO_LINGER
87 option is set for the socket with non-zero linger time, and the socket
88 has untransmitted data, then close() shall block for up to the current
89 linger interval until all data is transmitted.
90
92 Upon successful completion, 0 shall be returned; otherwise, -1 shall be
93 returned and errno set to indicate the error.
94
96 The close() function shall fail if:
97 EBADF The fildes argument is not a valid file descriptor.
99 EINTR The close() function was interrupted by a signal.
101 The close() function may fail if:
104 EIO An I/O error occurred while reading from or writing to the file
106 system.
107 The following sections are informative.
110
112 Reassigning a File Descriptor
113 The following example closes the file descriptor associated with stan‐
114 dard output for the current process, re-assigns standard output to a
115 new file descriptor, and closes the original file descriptor to clean
116 up. This example assumes that the file descriptor 0 (which is the
117 descriptor for standard input) is not closed.
118 #include <unistd.h>
121 ...
122 int pfd;
123 ...
124 close(1);
125 dup(pfd);
126 close(pfd);
127 ...
128 Incidentally, this is exactly what could be achieved using:
130 dup2(pfd, 1);
133 close(pfd);
134 Closing a File Descriptor
136 In the following example, close() is used to close a file descriptor
137 after an unsuccessful attempt is made to associate that file descriptor
138 with a stream.
139 #include <stdio.h>
142 #include <unistd.h>
143 #include <stdlib.h>
144 #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 ...
157
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.
163
165 The use of interruptible device close routines should be discouraged to
166 avoid problems with the implicit closes of file descriptors by exec and
167 exit(). This volume of IEEE Std 1003.1-2001 only intends to permit such
168 behavior by specifying the [EINTR] error condition.
169
171 None.
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174 STREAMS , fattach() , fclose() , fdetach() , fopen() , ioctl() , open()
175 , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>
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178 Portions of this text are reprinted and reproduced in electronic form
179 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
180 -- Portable Operating System Interface (POSIX), The Open Group Base
181 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
182 Electrical and Electronics Engineers, Inc and The Open Group. In the
183 event of any discrepancy between this version and the original IEEE and
184 The Open Group Standard, the original IEEE and The Open Group Standard
185 is the referee document. The original Standard can be obtained online
186 at http://www.opengroup.org/unix/online.html .
187IEEE/The Open Group 2003 CLOSE(P)