NAME
close —
delete a descriptor
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
int
close(int
fd);
DESCRIPTION
Theclose()
system 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)). 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 processes,
the close()
system 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(2) 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, FD_CLOEXEC)” 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
The close() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate the
error.
ERRORS
The close() system call will fail if:
- [
EBADF] - The fd argument is not an active descriptor.
- [
EINTR] - An interrupt was received.
- [
ENOSPC] - The underlying object did not fit, cached data was lost.
- [
ECONNRESET] - The underlying object was a stream socket that was shut down by the peer before all pending data was delivered.
In case of any error except EBADF, the
supplied file descriptor is deallocated and therefore is no longer
valid.
SEE ALSO
accept(2), closefrom(2), execve(2), fcntl(2), flock(2), open(2), pipe(2), socket(2), socketpair(2)
STANDARDS
The close() system call is expected to
conform to IEEE Std 1003.1-1990
(“POSIX.1”).
HISTORY
The close() function appeared in
Version 1 AT&T UNIX.