1close(2) System Calls close(2)
2
6 close - close a file descriptor
7
9 #include <unistd.h>
10 int close(int fildes);
12
15 The close() function deallocates the file descriptor indicated by
16 fildes. To deallocate means to make the file descriptor available for
17 return by subsequent calls to open(2) 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 will be removed (that is,
20 unlocked).
21 If close() is interrupted by a signal that is to be caught, it will
24 return −1 with errno set to EINTR and the state of fildes is unspeci‐
25 fied. If an I/O error occurred while reading from or writing to the
26 file system during close(), it returns -1, sets errno to EIO, and the
27 state of fildes is unspecified.
28 When all file descriptors associated with a pipe or FIFO special file
31 are closed, any data remaining in the pipe or FIFO will be discarded.
32 When all file descriptors associated with an open file description have
35 been closed the open file description will be freed.
36 If the link count of the file is 0, when all file descriptors associ‐
39 ated with the file are closed, the space occupied by the file will be
40 freed and the file will no longer be accessible.
41 If a streams-based (see Intro(2)) fildes is closed and the calling
44 process was previously registered to receive a SIGPOLL signal (see sig‐
45 nal(3C)) for events associated with that stream (see I_SETSIG in
46 streamio(7I)), the calling process will be unregistered for events
47 associated with the stream. The last close() for a stream causes the
48 stream associated with fildes to be dismantled. If O_NONBLOCK and
49 O_NDELAY are not set and there have been no signals posted for the
50 stream, and if there is data on the module's write queue, close() waits
51 up to 15 seconds (for each module and driver) for any output to drain
52 before dismantling the stream. The time delay can be changed via an
53 I_SETCLTIME ioctl(2) request (see streamio(7I)). If the O_NONBLOCK or
54 O_NDELAY flag is set, or if there are any pending signals, close() does
55 not wait for output to drain, and dismantles the stream immediately.
56 If fildes is associated with one end of a pipe, the last close() causes
59 a hangup to occur on the other end of the pipe. In addition, if the
60 other end of the pipe has been named by fattach(3C), then the last
61 close() forces the named end to be detached by fdetach(3C). If the
62 named end has no open file descriptors associated with it and gets
63 detached, the stream associated with that end is also dismantled.
64 If fildes refers to the master side of a pseudo-terminal, a SIGHUP sig‐
67 nal is sent to the session leader, if any, for which the slave side of
68 the pseudo-terminal is the controlling terminal. It is unspecified
69 whether closing the master side of the pseudo-terminal flushes all
70 queued input and output.
71 If fildes refers to the slave side of a streams-based pseudo-terminal,
74 a zero-length message may be sent to the master.
75 When there is an outstanding cancelable asynchronous I/O operation
78 against fildes when close() is called, that I/O operation is canceled.
79 An I/O operation that is not canceled completes as if the close() oper‐
80 ation had not yet occurred. All operations that are not canceled will
81 complete as if the close() blocked until the operations completed.
82 If a shared memory object or a memory mapped file remains referenced at
85 the last close (that is, a process has it mapped), then the entire con‐
86 tents of the memory object will persist until the memory object becomes
87 unreferenced. If this is the last close of a shared memory object or a
88 memory mapped file and the close results in the memory object becoming
89 unreferenced, and the memory object has been unlinked, then the memory
90 object will be removed.
91 If fildes refers to a socket, close() causes the socket to be
94 destroyed. If the socket is connection-mode, and the SO_LINGER option
95 is set for the socket with non-zero linger time, and the socket has
96 untransmitted data, then close() will block for up to the current
97 linger interval until all data is transmitted.
98
100 Upon successful completion, 0 is returned. Otherwise, −1 is returned
101 and errno is set to indicate the error.
102
104 The close() function will fail if:
105 EBADF The fildes argument is not a valid file descriptor.
107 EINTR The close() function was interrupted by a signal.
110 ENOLINK The fildes argument is on a remote machine and the link to
113 that machine is no longer active.
114 ENOSPC There was no free space remaining on the device containing
117 the file.
118 The close() function may fail if:
122 EIO An I/O error occurred while reading from or writing to the file
124 system.
125
128 Example 1 Reassign a file descriptor.
129 The following example closes the file descriptor associated with stan‐
132 dard output for the current process, re-assigns standard output to a
133 new file descriptor, and closes the original file descriptor to clean
134 up. This example assumes that the file descriptor 0, which is the
135 descriptor for standard input, is not closed.
136 #include <unistd.h>
139 ...
140 int pfd;
141 ...
142 close(1);
143 dup(pfd);
144 close(pfd);
145 ...
146 Incidentally, this is exactly what could be achieved using:
150 dup2(pfd, 1);
153 close(pfd);
154 Example 2 Close a file descriptor.
157 In the following example, close() is used to close a file descriptor
160 after an unsuccessful attempt is made to associate that file descriptor
161 with a stream.
162 #include <stdio.h>
165 #include <unistd.h>
166 #include <stdlib.h>
167 #define LOCKFILE "/etc/ptmp"
169 ...
170 int pfd;
171 FILE *fpfd;
172 ...
173 if ((fpfd = fdopen (pfd, "w")) == NULL) {
174 close(pfd);
175 unlink(LOCKFILE);
176 exit(1);
177 }
178 ...
179
182 An application that used the stdio function fopen(3C) to open a file
183 should use the corresponding fclose(3C) function rather than close().
184
186 See attributes(5) for descriptions of the following attributes:
187 ┌─────────────────────────────┬─────────────────────────────┐
192 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
193 ├─────────────────────────────┼─────────────────────────────┤
194 │Interface Stability │Standard │
195 ├─────────────────────────────┼─────────────────────────────┤
196 │MT-Level │Async-Signal-Safe │
197 └─────────────────────────────┴─────────────────────────────┘
198
200 Intro(2), creat(2), dup(2), exec(2), fcntl(2), ioctl(2), open(2)
201 pipe(2), fattach(3C), fclose(3C), fdetach(3C), fopen(3C), signal(3C),
202 signal.h(3HEAD), attributes(5), standards(5), streamio(7I)
203SunOS 5.11 18 Oct 2005 close(2)