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CLOSE(2)                   Linux Programmer's Manual                  CLOSE(2)

NAME
       close - close a file descriptor
SYNOPSIS
       #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
       SVr4, 4.3BSD, POSIX.1-2001.
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.
       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 file system 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.
       When dealing with sockets, you have to be sure that there is no recv(2)
       still blocking on it on another thread, otherwise it might  block  for-
       ever,  since  no  more messages will be send via the socket. Be sure to
       use shutdown(2) to shut down all parts the  connection  before  closing
       the socket.
SEE ALSO
       fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)
COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                             2007-12-28                          CLOSE(2)