NAME
close —
delete a descriptor
SYNOPSIS
#include
<unistd.h>
int
close(int
d);
DESCRIPTION
The
close()
call deletes a descriptor d from the per-process
object reference 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 discarded; 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 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 process 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) restores the
default, which is to not close the descriptor.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
close() will fail if:
- [
EBADF] - d is not an active descriptor.
- [
EINTR] - An interrupt was received.
- [
EIO] - An I/O error occurred while writing to the file system.
SEE ALSO
accept(2), closefrom(2), dup2(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)
STANDARDS
close() conforms to IEEE
Std 1003.1-2008 (“POSIX.1”).
HISTORY
The close() system call first appeared in
Version 1 AT&T UNIX.