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 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.
close() returns zero on success. On error, -1 is returned, and errno is set appropri-
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.
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 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
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 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.
fcntl(2), fsync(2), open(2), shutdown(2), unlink(2), fclose(3)
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Linux 2007-12-28 CLOSE(2)