close

       #include <unistd.h>

       int close(int fd);

DESCRIPTION
       close()  closes  a  file descriptor, so that it no longer refers to any
       file and may be reused.  Any record locks (see fcntl(2))  held  on  the
       file  it  was  associated  with,  and owned by the process, are removed
       (regardless of the file descriptor that was used to obtain the lock).

       If fd is the last file descriptor referring to the underlying open file
       description  (see open(2)), the resources associated with the open file
       description are freed; if the descriptor was the last  reference  to  a
       file which has been removed using unlink(2), the file is deleted.

RETURN VALUE
       close()  returns  zero on success.  On error, -1 is returned, and errno
       is set appropriately.

ERRORS
       EBADF  fd isn't a valid open file descriptor.

       EINTR  The close() call was interrupted by a signal; see signal(7).

       EIO    An I/O error occurred.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES
       Not checking the return value of close() is a common  but  nevertheless
       serious  programming error.  It is quite possible that errors on a pre-
       vious write(2) operation are first reported at the final close().   Not
       checking the return value when closing the file may lead to silent loss
       of data.  This can especially be observed with NFS and with disk quota.
       Note  that  the  return  value should be used only for diagnostics.  In
       particular close() should not be retried after an EINTR since this  may
       cause a reused descriptor from another thread to be closed.

       A  successful  close does not guarantee that the data has been success-
       fully saved to disk, as the kernel defers writes.  It is not common for
       a  filesystem  to  flush the buffers when the stream is closed.  If you
       need to be sure that the data is physically stored, use fsync(2).   (It
       will depend on the disk hardware at this point.)

       It  is  probably  unwise to close file descriptors while they may be in
       use by system calls in other threads in the same process.  Since a file
       descriptor  may  be reused, there are some obscure race conditions that
       may cause unintended side effects.

SEE ALSO
       fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)

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