CLOSE(2) BSD Programmer's Manual CLOSE(2)
close - delete a descriptor
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 discard-
ed; on the last close of a file holding an advisory lock the lock is re-
leased (see further flock(2)).
When a process exits, all associated file descriptors are freed, but
since there is a limit on active descriptors per processes, the close()
function call is useful when a large quantity of file descriptors are be-
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 is then to 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 is at-
tempted, but if some of these descriptors will still be needed if the ex-
ecve fails, it is necessary to arrange for them to be closed if the ex-
ecve succeeds. For this reason, the call ``fcntl(d, F_SETFD, 1)'' is
provided, which arranges that a descriptor will be closed after a suc-
cessful execve; the call ``fcntl(d, F_SETFD, 0)'' restores 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), flock(2), open(2), pipe(2), socket(2), socketpair(2),
Close() conforms to IEEE Std 1003.1-1988 (``POSIX'').
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