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 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.
RETURN VALUE close() returns zero on success. On error, -1 is returned, and errno is set appropriately.
ERRORS EBADF fd isnt a valid open file descriptor.
EINTR The close() call was interrupted by a signal.
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 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 the socket.
SEE ALSO fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)
Linux 2001-12-13 CLOSE(2)