NAME
close —
delete a descriptor
SYNOPSIS
#include
<unistd.h>
int
close(int fildes);
DESCRIPTION
The
close()
call deletes a descriptor 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; on the last
close of a file holding an advisory lock the lock is released (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 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 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 attempted, but if
some of these descriptors will still be needed if the execve fails, it is
necessary to arrange for them to be closed if the execve succeeds. For this
reason, the call “fcntl(d, F_SETFD,
1)” is provided, which arranges that a descriptor will be
closed after a successful execve; the call “fcntl(d,
F_SETFD, 0)” restores the default, which is to not close the
descriptor.
RETURN VALUES
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 indicate the error.
ERRORS
The close() system call will fail if:
- [
EBADF] - fildes is not a valid, active file descriptor.
- [
EINTR] - Its execution was interrupted by a signal.
- [
EIO] - A previously-uncommitted write(2) encountered an input/output error.
SEE ALSO
accept(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)
STANDARDS
close() conforms to IEEE
Std 1003.1-1988 (“POSIX.1”).