# close

## PROLOG



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


## NAME



           close — close a file descriptor
    


## SYNOPSIS



           #include <unistd.h>
    
           int close(int _fildes_);
    


## DESCRIPTION



           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).
    
           If _close_() is interrupted by a signal that is to be caught, it
           shall return -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 system during _close_(), it may return -1 with
           _errno_ set to **[EIO]** ; if this error is returned, 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 shall be
           discarded.
    
           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.
    
           If a 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
           I_SETCLTIME _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 STREAM immediately.
    
           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 by _fattach_(), then the last
           _close_() shall force the named end to be detached by _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 I/O 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 I/O 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, and the 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.
    


## RETURN VALUE



           Upon successful completion, 0 shall be returned; otherwise, -1
           shall be returned and _errno_ set to indicate the error.
    


## ERRORS



           The _close_() function shall fail if:
    
           **EBADF** The _fildes_ argument is not a open file descriptor.
    
           **EINTR** The _close_() function was interrupted by a signal.
    
           The _close_() function may fail if:
    
           **EIO** An I/O error occurred while reading from or writing to the
                  file system.
    
           _The following sections are informative._
    


## EXAMPLES



       **Reassigning a File Descriptor**
           The following example closes the file descriptor associated with
           standard 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 descriptor for standard input) is not
           closed.
    
               #include <unistd.h>
               ...
               int pfd;
               ...
               close(1);
               dup(pfd);
               close(pfd);
               ...
    
           Incidentally, this is exactly what could be achieved using:
    
               dup2(pfd, 1);
               close(pfd);
    
       **Closing 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);
               }
               ...
    


## APPLICATION USAGE



           An application that had used the _stdio_ routine _fopen_() to open a
           file should use the corresponding _fclose_() routine rather than
           _close_().  Once a file is closed, the file descriptor no longer
           exists, since the integer corresponding to it no longer refers to
           a file.
    
           Implementations may use file descriptors that must be inherited
           into child processes for the child process to remain conforming,
           such as for message catalog or tracing purposes. Therefore, an
           application that calls _close_() on an arbitrary integer risks non-
           conforming behavior, and _close_() can only portably be used on file
           descriptor values that the application has obtained through
           explicit actions, as well as the three file descriptors
           corresponding to the standard file streams. In multi-threaded
           parent applications, the practice of calling _close_() in a loop
           after _fork_() and before an _exec_ call in order to avoid a race
           condition of leaking an unintended file descriptor into a child
           process, is therefore unsafe, and the race should instead be
           combatted by opening all file descriptors with the FD_CLOEXEC bit
           set unless the file descriptor is intended to be inherited across
           _exec_.
    
           Usage of _close_() on file descriptors STDIN_FILENO, STDOUT_FILENO,
           or STDERR_FILENO should immediately be followed by an operation to
           reopen these file descriptors. Unexpected behavior will result if
           any of these file descriptors is left in a closed state (for
           example, an **[EBADF]** error from _perror_()) or if an unrelated _open_()
           or similar call later in the application accidentally allocates a
           file to one of these well-known file descriptors. Furthermore, a
           _close_() followed by a reopen operation (e.g., _open_(), _dup_(), etc.)
           is not atomic; _dup2_() should be used to change standard file
           descriptors.
    


## RATIONALE



           The use of interruptible device close routines should be
           discouraged to avoid problems with the implicit closes of file
           descriptors by _exec_ and _exit_().  This volume of POSIX.1‐2017 only
           intends to permit such behavior by specifying the **[EINTR]** error
           condition.
    
           Note that the requirement for _close_() on a socket to block for up
           to the current linger interval is not conditional on the
           O_NONBLOCK setting.
    
           The standard developers rejected a proposal to add _closefrom_() to
           the standard. Because the standard permits implementations to use
           inherited file descriptors as a means of providing a conforming
           environment for the child process, it is not possible to
           standardize an interface that closes arbitrary file descriptors
           above a certain value while still guaranteeing a conforming
           environment.
    


## FUTURE DIRECTIONS



           None.
    


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