NetBSD/lib/libc/sys/close.2

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.\" $NetBSD: close.2,v 1.15 2003/08/07 16:43:56 agc Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
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.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\"
.\" @(#)close.2 8.2 (Berkeley) 4/19/94
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.\"
.Dd April 19, 1994
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.Dt CLOSE 2
.Os
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.Sh NAME
.Nm close
.Nd delete a descriptor
.Sh LIBRARY
.Lb libc
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.Sh SYNOPSIS
.In unistd.h
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.Ft int
.Fn close "int d"
.Sh DESCRIPTION
The
.Fn close
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system call deletes a descriptor from the per-process object
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reference table.
If this is the last reference to the underlying object, the
object will be deactivated.
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For example, on the last close of a file the current
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.Em seek
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pointer associated with the file is lost; on the last close of a
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.Xr socket 2
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associated naming information and queued data are discarded; on
the last close of a file holding an advisory lock the lock is
released (see
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.Xr flock 2 ) .
.Pp
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When a process exits, all associated descriptors are freed, but
since there is a limit on active descriptors per processes, the
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.Fn close
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system call
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is useful when a large quantity of file descriptors are being handled.
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.Pp
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When a process calls
.Xr fork 2 ,
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all descriptors for the new child process reference the same
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objects as they did in the parent before the
.Fn fork .
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If a new process is then to be run using
.Xr execve 2 ,
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the process would normally inherit these descriptors.
Most of the descriptors can be rearranged with
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.Xr dup2 2
or deleted with
.Fn close
before the
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.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
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is provided,
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which arranges that a descriptor
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.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 .
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.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
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will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa d
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is not an active descriptor.
.It Bq Er EINTR
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An interrupt was received.
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.El
.Sh SEE ALSO
.Xr accept 2 ,
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.Xr execve 2 ,
.Xr fcntl 2 ,
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.Xr flock 2 ,
.Xr open 2 ,
.Xr pipe 2 ,
.Xr socket 2 ,
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.Xr socketpair 2
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.Sh STANDARDS
The
.Fn close
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function conforms to
.St -p1003.1-90 .