int close(int fildes);
IEEE Std 1003.1-2017
The purpose is to close a file descriptor. The
close() function shall deallocate the file descriptor indicated by fildes. To deallocate 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).
close() is interrupted by a signal that is to be caught, it shall return
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
When all file descriptors associated with a pipe or
FIFO special file are closed, any data remaining in the pipe or
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.
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
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
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
fattach(), then the last
close() shall force the named end to be detached
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 message may be sent to the master.
When there is an outstanding cancelable asynchronous
I/O operation against fildes when
close() is called, that
operation may be canceled. An
I/O operation that is not canceled 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
operation may be canceled upon
close(), is implementation-defined.
If a memory mapped file or a shared memory object 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 memory mapped file or a shared memory object 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,
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.
Upon successful completion,
0 shall be returned, otherwise,
-1 shall be returned and
errno set to indicate the error.
close() function shall fail if:
EBADF- The fildes argument is not a open file descriptor.
close()function was interrupted by a signal.
close() function may fail if:
EIO- An I/O error occurred while reading from or writing to the file system.