CLOSE(2) | System Calls Manual | CLOSE(2) |
close
— delete a
descriptor
#include
<unistd.h>
int
close
(int
d);
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 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 being
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 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.
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.
close
() will fail if:
accept(2), closefrom(2), dup2(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)
close
() conforms to IEEE
Std 1003.1-2008 (“POSIX.1”).
The close
() system call first appeared in
Version 1 AT&T UNIX.
December 10, 2014 | OpenBSD-6.4 |