NetBSD/lib/libc/sys/close.2

.\"	$NetBSD: close.2,v 1.15 2003/08/07 16:43:56 agc Exp $
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.\"     @(#)close.2	8.2 (Berkeley) 4/19/94
.\"
.Dd April 19, 1994
.Dt CLOSE 2
.Os
.Sh NAME
.Nm close
.Nd delete a descriptor
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn close "int d"
.Sh DESCRIPTION
The
.Fn close
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
.Em seek
pointer associated with the file is lost; on the last close of a
.Xr 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
.Xr flock 2 ) .
.Pp
When a process exits, all associated descriptors are freed, but
since there is a limit on active descriptors per processes, the
.Fn close
system call
is useful when a large quantity of file descriptors are being handled.
.Pp
When a process calls
.Xr fork 2 ,
all descriptors for the new child process reference the same
objects as they did in the parent before the
.Fn fork .
If a new process is then to be run using
.Xr execve 2 ,
the process would normally inherit these descriptors.
Most of the descriptors can be rearranged with
.Xr dup2 2
or deleted with
.Fn close
before the
.Fn execve
is attempted, but if some of these descriptors will still be needed if the
.Fn execve
fails, it is necessary to arrange for them to be closed only if the
.Fn execve
succeeds.
For this reason, the system call
.Bl -item -offset indent
.It
.Fn fcntl d F_SETFD 1 ;
.El
.Pp
is provided,
which arranges that a descriptor
.Dq Fa d
will be closed after a successful
.Fn execve ;
the system call
.Bl -item -offset indent
.It
.Fn fcntl d F_SETFD 0 ;
.El
.Pp
restores the default, which is to not close descriptor
.Dq Fa d .
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and the global integer variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn close
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa d
is not an active descriptor.
.It Bq Er EINTR
An interrupt was received.
.El
.Sh SEE ALSO
.Xr accept 2 ,
.Xr execve 2 ,
.Xr fcntl 2 ,
.Xr flock 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
.Xr socketpair 2
.Sh STANDARDS
The
.Fn close
function conforms to
.St -p1003.1-90 .