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 appropri-
       ately.

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 previous 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 successfully 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 forever, 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)