CLOSE(2) BSD System Calls Manual CLOSE(2)
close -- delete a descriptor
The close() call deletes a descriptor d from the per-process object ref-
erence 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
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 descrip-
tors 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 descrip-
tor 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
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 sys-
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.
BSD March 30, 2017 BSD