CLOSE(2) Linux Programmer's Manual CLOSE(2)
close - close a file descriptor
int close(int fd);
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 copy of a particular file descriptor the resources
associated with it are freed; if the descriptor was the last reference
to a file which has been removed using unlink(2) the file is deleted.
close() returns zero on success. On error, -1 is returned, and errno
is set appropriately.
EBADF fd isn't a valid open file descriptor.
EINTR The close() call was interrupted by a signal.
EIO An I/O error occurred.
SVr4, 4.3BSD, POSIX.1-2001.
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 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 re-used, 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 sent via the socket. Be sure to
use shutdown(2) to shut down all parts the connection before closing
fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)
Linux 2001-12-13 CLOSE(2)