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close(2)
close(2) System Calls close(2)
NAME
close - close a file descriptor
SYNOPSIS
#include <unistd.h>
int close(int fildes);
DESCRIPTION
The close() function deallocates the file descriptor indicated by
fildes. To deallocate means to make the file descriptor available for
return by subsequent calls to open(2) or other functions that allocate
file descriptors. All outstanding record locks owned by the process on
the file associated with the file descriptor will be removed (that is,
unlocked).
If close() is interrupted by a signal that is to be caught, it will re‐
turn −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 sys‐
tem during close(), it returns -1, sets errno to EIO, and 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 will be discarded.
When all file descriptors associated with an open file description have
been closed, the open file description will be freed.
If the link count of the file is 0, when all file descriptors associ‐
ated with the file are closed, the space occupied by the file will be
freed and the file will no longer be accessible.
If a streams-based (see Intro(2)) fildes is closed and the calling
process was previously registered to receive a SIGPOLL signal (see sig‐
nal(3C)) for events associated with that stream (see I_SETSIG in
streamio(4I)), the calling process will be unregistered for events as‐
sociated with the stream. The last close() for a stream causes the
stream associated with fildes to be dismantled. If O_NONBLOCK and
O_NDELAY are not set and there have been no signals posted for the
stream, and if there is data on the module's write queue, close() waits
up to 15 seconds (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(2) request (see streamio(4I)). If the O_NONBLOCK or
O_NDELAY flag is set, or if there are any pending signals, close() does
not wait for output to drain, and dismantles the stream immediately.
If fildes is associated with one end of a pipe, the last close() causes
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(3C), then the last
close() forces the named end to be detached by fdetach(3C). If the
named end has no open file descriptors associated with it and gets de‐
tached, the stream associated with that end is also dismantled.
If fildes refers to the manager side of a pseudo-terminal, a SIGHUP
signal is sent to the session leader, if any, for which the subsidiary
side of the pseudo-terminal is the controlling terminal. It is unspeci‐
fied whether closing the manager side of the pseudo-terminal flushes
all queued input and output.
If fildes refers to the subsidiary side of a streams-based pseudo-ter‐
minal, a zero-length message may be sent to the manager.
When there is an outstanding cancelable asynchronous I/O operation
against fildes when close() is called, that I/O operation is canceled.
An I/O operation that is not canceled completes as if the close() oper‐
ation had not yet occurred. All operations that are not canceled will
complete as if the close() blocked until the operations completed.
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 con‐
tents of the memory object will 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 will be removed.
When all file descriptors associated with a socket have been closed,
the socket shall be destroyed. If the socket is 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() will block for up
to the current linger interval until all data is transmitted.
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, −1 is returned
and errno is set to indicate the error.
ERRORS
The close() function will fail if:
EBADF The fildes argument is not a valid file descriptor.
EINTR The close() function was interrupted by a signal.
ENOLINK The fildes argument is on a remote machine and the link to
that machine is no longer active.
ENOSPC There was no free space remaining on the device containing
the file.
The close() function may fail if:
EIO An I/O error occurred while reading from or writing to the file
system.
EXAMPLES
Example 1 Reassign a file descriptor.
The following example closes the file descriptor associated with stan‐
dard 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 de‐
scriptor for standard input, is not closed; and that no other threads
in the process are opening or closing file descriptors at the same
time.
#include <unistd.h>
...
int pfd;
...
close(1);
dup(pfd);
close(pfd);
...
This can be achieved more simply, and in a threadsafe manner, with
dup(2):
dup2(pfd, 1);
close(pfd);
Example 2 Close 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);
}
...
USAGE
An application that uses the stdio function fopen(3C) to open a file,
or which uses the fdopen(3C) function to associate a stream with a file
descriptor, should use the corresponding fclose(3C) function on the
file streams returned from those functions rather than using the
close() function on the underlying file descriptor.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee standards(7).
SEE ALSO
dup(2), creat(2), exec(2), fcntl(2), Intro(2), ioctl(2), open(2),
pipe(2), fattach(3C), fclose(3C), fdetach(3C), fopen(3C), signal(3C),
socket(3C), signal.h(3HEAD), streamio(4I), attributes(7), standards(7)
HISTORY
The close() function has been included in all Sun and Oracle releases
of Solaris.
Oracle Solaris 11.4 19 Jun 2024 close(2)