7e6cabd06e
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
327 lines
6.9 KiB
Groff
327 lines
6.9 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 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
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd August 8, 2013
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.Dt MKTEMP 3
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.Os
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.Sh NAME
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.Nm mktemp
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.Nd make temporary file name (unique)
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft char *
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.Fn mktemp "char *template"
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.Ft int
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.Fn mkstemp "char *template"
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.Ft int
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.Fn mkostemp "char *template" "int oflags"
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.Ft int
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.Fn mkostemps "char *template" "int suffixlen" "int oflags"
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.Ft char *
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.Fn mkdtemp "char *template"
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.In unistd.h
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.Ft int
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.Fn mkstemps "char *template" "int suffixlen"
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.Sh DESCRIPTION
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The
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.Fn mktemp
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function
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takes the given file name template and overwrites a portion of it
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to create a file name.
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This file name is guaranteed not to exist at the time of function invocation
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and is suitable for use
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by the application.
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The template may be any file name with some number of
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.Ql X Ns s
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appended
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to it, for example
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.Pa /tmp/temp.XXXXXX .
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The trailing
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.Ql X Ns s
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are replaced with a
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unique alphanumeric combination.
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The number of unique file names
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.Fn mktemp
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can return depends on the number of
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.Ql X Ns s
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provided; six
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.Ql X Ns s
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will
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result in
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.Fn mktemp
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selecting one of 56800235584 (62 ** 6) possible temporary file names.
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.Pp
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The
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.Fn mkstemp
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function
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makes the same replacement to the template and creates the template file,
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mode 0600, returning a file descriptor opened for reading and writing.
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This avoids the race between testing for a file's existence and opening it
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for use.
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.Pp
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The
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.Fn mkostemp
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function
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is like
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.Fn mkstemp
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but allows specifying additional
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.Xr open 2
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flags (defined in
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.In fcntl.h ) .
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The permitted flags are
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.Dv O_APPEND ,
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.Dv O_DIRECT ,
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.Dv O_SHLOCK ,
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.Dv O_EXLOCK ,
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.Dv O_SYNC
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and
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.Dv O_CLOEXEC .
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.Pp
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The
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.Fn mkstemps
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and
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.Fn mkostemps
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functions act the same as
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.Fn mkstemp
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and
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.Fn mkostemp
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respectively,
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except they permit a suffix to exist in the template.
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The template should be of the form
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.Pa /tmp/tmpXXXXXXsuffix .
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The
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.Fn mkstemps
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and
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.Fn mkostemps
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function
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are told the length of the suffix string.
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.Pp
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The
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.Fn mkdtemp
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function makes the same replacement to the template as in
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.Fn mktemp
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and creates the template directory, mode 0700.
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.Sh RETURN VALUES
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The
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.Fn mktemp
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and
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.Fn mkdtemp
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functions return a pointer to the template on success and
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.Dv NULL
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on failure.
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The
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.Fn mkstemp ,
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.Fn mkostemp
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.Fn mkstemps
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and
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.Fn mkostemps
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functions
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return \-1 if no suitable file could be created.
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If either call fails an error code is placed in the global variable
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.Va errno .
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.Sh ERRORS
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The
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.Fn mkstemp ,
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.Fn mkostemp ,
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.Fn mkstemps ,
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.Fn mkostemps
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and
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.Fn mkdtemp
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functions
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may set
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.Va errno
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to one of the following values:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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The pathname portion of the template is not an existing directory.
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.El
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.Pp
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The
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.Fn mkostemp
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and
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.Fn mkostemps
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functions
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may also set
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.Va errno
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to the following value:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa oflags
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argument is invalid.
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.El
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.Pp
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The
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.Fn mkstemp ,
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.Fn mkostemp ,
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.Fn mkstemps ,
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.Fn mkostemps
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and
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.Fn mkdtemp
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functions
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may also set
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.Va errno
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to any value specified by the
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.Xr stat 2
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function.
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.Pp
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The
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.Fn mkstemp ,
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.Fn mkostemp ,
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.Fn mkstemps
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and
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.Fn mkostemps
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functions
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may also set
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.Va errno
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to any value specified by the
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.Xr open 2
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function.
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.Pp
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The
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.Fn mkdtemp
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function
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may also set
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.Va errno
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to any value specified by the
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.Xr mkdir 2
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function.
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.Sh NOTES
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A common problem that results in a core dump is that the programmer
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passes in a read-only string to
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.Fn mktemp ,
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.Fn mkstemp ,
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.Fn mkstemps
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or
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.Fn mkdtemp .
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This is common with programs that were developed before
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.St -isoC
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compilers were common.
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For example, calling
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.Fn mkstemp
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with an argument of
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.Qq /tmp/tempfile.XXXXXX
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will result in a core dump due to
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.Fn mkstemp
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attempting to modify the string constant that was given.
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.Pp
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The
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.Fn mkdtemp ,
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.Fn mkstemp
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and
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.Fn mktemp
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function prototypes are also available from
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.In unistd.h .
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.Sh SEE ALSO
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.Xr chmod 2 ,
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.Xr getpid 2 ,
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.Xr mkdir 2 ,
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.Xr open 2 ,
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.Xr stat 2
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.Sh STANDARDS
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The
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.Fn mkstemp
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and
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.Fn mkdtemp
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functions are expected to conform to
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.St -p1003.1-2008 .
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The
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.Fn mktemp
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function is expected to conform to
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.St -p1003.1-2001
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and is not specified by
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.St -p1003.1-2008 .
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The
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.Fn mkostemp ,
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.Fn mkstemps
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and
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.Fn mkostemps
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functions do not conform to any standard.
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.Sh HISTORY
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A
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.Fn mktemp
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function appeared in
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.At v7 .
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The
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.Fn mkstemp
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function appeared in
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.Bx 4.4 .
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The
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.Fn mkdtemp
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function first appeared in
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.Ox 2.2 ,
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and later in
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.Fx 3.2 .
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The
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.Fn mkstemps
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function first appeared in
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.Ox 2.4 ,
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and later in
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.Fx 3.4 .
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The
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.Fn mkostemp
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and
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.Fn mkostemps
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functions appeared in
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.Fx 10.0 .
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.Sh BUGS
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This family of functions produces filenames which can be guessed,
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though the risk is minimized when large numbers of
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.Ql X Ns s
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are used to
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increase the number of possible temporary filenames.
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This makes the race in
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.Fn mktemp ,
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between testing for a file's existence (in the
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.Fn mktemp
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function call)
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and opening it for use
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(later in the user application)
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particularly dangerous from a security perspective.
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Whenever it is possible,
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.Fn mkstemp
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or
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.Fn mkostemp
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should be used instead, since it does not have the race condition.
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If
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.Fn mkstemp
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cannot be used, the filename created by
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.Fn mktemp
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should be created using the
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.Dv O_EXCL
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flag to
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.Xr open 2
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and the return status of the call should be tested for failure.
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This will ensure that the program does not continue blindly
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in the event that an attacker has already created the file
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with the intention of manipulating or reading its contents.
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