CLOSE(2) BSD Programmer's Manual CLOSE(2)
close - delete a descriptor
#include <unistd.h>
int
close(int d);
The close() call deletes a descriptor from the per-process object refer-
ence table. If this is the last reference to the underlying object, the
object will be deactivated. For example, on the last close of a file, the
current seek pointer associated with the file is lost; on the last close
of a socket(2), associated naming information and queued data are dis-
carded; and on the last close of a file holding an advisory lock, the
lock is released (see flock(2)). However, the semantics of System V and
IEEE Std 1003.1-1988 ("POSIX.1") dictate that all fcntl(2) advisory
record locks associated with a file for a given process are removed when
any file descriptor for that file is closed by that process.
When a process exits, all associated file descriptors are freed, but
since there is a limit on active descriptors per process, the close()
function call is useful when a large quantity of file descriptors are be-
ing handled.
When a process forks (see fork(2)), all descriptors for the new child
process reference the same objects as they did in the parent before the
fork. If a new process image is to then be run using execve(2), the pro-
cess would normally inherit these descriptors. Most of the descriptors
can be rearranged with dup2(2) or deleted with close() before the
execve(2) is attempted, but since some of these descriptors may still be
needed should the execve(2) fail, it is necessary to arrange for them to
be closed when the execve(2) succeeds. For this reason, the call fcntl(d,
F_SETFD, FD_CLOEXEC) is provided, which arranges that a descriptor will
be closed after a successful execve(2); the call fcntl(d, F_SETFD, 0) re-
stores the default, which is to not close the descriptor.
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and the global integer variable errno is set to indi-
cate the error.
close() will fail if:
[EBADF] d is not an active descriptor.
[EINTR] An interrupt was received.
accept(2), closefrom(2), execve(2), fcntl(2), flock(2), open(2), pipe(2),
socket(2), socketpair(2)
close() conforms to IEEE Std 1003.1-1988 ("POSIX.1").
MirBSD #10-current April 19, 1994 1