man3/mkstemp.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright (C) 2008, Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\"
   4 .\" Permission is granted to make and distribute verbatim copies of this
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   9 .\" manual under the conditions for verbatim copying, provided that the
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  11 .\" permission notice identical to this one.
  12 .\"
  13 .\" Since the Linux kernel and libraries are constantly changing, this
  14 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  15 .\" responsibility for errors or omissions, or for damages resulting from
  16 .\" the use of the information contained herein.  The author(s) may not
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  21 .\" Formatted or processed versions of this manual, if unaccompanied by
  22 .\" the source, must acknowledge the copyright and authors of this work.
  23 .\"
  24 .\" References consulted:
  25 .\"     Linux libc source code
  26 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  27 .\"     386BSD man pages
  28 .\" Modified Sat Jul 24 18:48:48 1993 by Rik Faith (faith@cs.unc.edu)
  29 .\" Modified 980310, aeb
  30 .\" Modified 990328, aeb
  31 .\" 2008-06-19, mtk, Added mkostemp(); various other changes
  32 .\"
  33 .TH MKSTEMP 3  2010-09-20 "GNU" "Linux Programmer's Manual"
  34 .SH NAME
  35 mkstemp, mkostemp \- create a unique temporary file
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <stdlib.h>
  39 .sp
  40 .BI "int mkstemp(char *" template );
  41 .sp
  42 .BI "int mkostemp (char *" template ", int " flags );
  43 .sp
  44 .BI "int mkstemps(char *" template ", int " suffixlen );
  45 .sp
  46 .BI "int mkostemps(char *" template ", int " suffixlen ", int " flags );
  47 .fi
  48 .sp
  49 .in -4n
  50 Feature Test Macro Requirements for glibc (see
  51 .BR feature_test_macros (7)):
  52 .in
  53 .sp
  54 .BR mkstemp ():
  55 .ad l
  56 .RS 4
  57 .PD 0
  58 .TP 4
  59 Since glibc 2.12:
  60 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  61 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED ||
  62 _POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
  63 .TP
  64 Before glibc 2.12:
  65 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  66 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  67 .PD
  68 .RE
  69 .ad b
  70 .PP
  71 .BR mkostemp ():
  72 _GNU_SOURCE
  73 .br
  74 .BR mkstemps ():
  75 _BSD_SOURCE || _SVID_SOURCE
  76 .br
  77 .BR mkostemps ():
  78 _GNU_SOURCE
  79 .SH DESCRIPTION
  80 The
  81 .BR mkstemp ()
  82 function generates a unique temporary filename from
  83 .IR template ,
  84 creates and opens the file,
  85 and returns an open file descriptor for the file.
  86
  87 The last six characters of
  88 .I template
  89 must be "XXXXXX" and these are replaced with a string that makes the
  90 filename unique.
  91 Since it will be modified,
  92 .I template
  93 must not be a string constant, but should be declared as a character array.
  94
  95 The file is created with
  96 permissions 0600, that is, read plus write for owner only.
  97 (In glibc versions 2.06 and earlier, the file is created with permissions 0666,
  98 that is, read and write for all users.)
  99 The returned file descriptor provides both read and write access to the file.
 100 The file is opened with the
 101 .BR open (2)
 102 .B O_EXCL
 103 flag, guaranteeing that the caller is the process that creates the file.
 104
 105 The
 106 .BR mkostemp ()
 107 function is like
 108 .BR mkstemp (),
 109 with the difference that flags as for
 110 .BR open (2)
 111 may be specified in
 112 .IR flags
 113 (e.g.,
 114 .BR O_APPEND ,
 115 .BR O_SYNC ).
 116
 117 The
 118 .BR mkstemps ()
 119 function is like
 120 .BR mkstemp (),
 121 except that the string in
 122 .I template
 123 contains a suffix of
 124 .I suffixlen
 125 characters.
 126 Thus,
 127 .I template
 128 is of the form
 129 .IR "prefixXXXXXXsuffix" ,
 130 and the string XXXXXX is modified as for
 131 .BR mkstemp ().
 132
 133 The
 134 .BR mkostemps ()
 135 function is to
 136 .BR mkstemps ()
 137 as
 138 .BR mkostemp ()
 139 is to
 140 .BR mkstemp ().
 141 .SH "RETURN VALUE"
 142 On success, these functions return the file descriptor
 143 of the temporary file.
 144 On error, \-1 is returned, and
 145 .I errno
 146 is set appropriately.
 147 .SH ERRORS
 148 .TP
 149 .B EEXIST
 150 Could not create a unique temporary filename.
 151 Now the contents of \fItemplate\fP are undefined.
 152 .TP
 153 .B EINVAL
 154 For
 155 .BR mkstemp ()
 156 and
 157 .BR mkostemp ():
 158 The last six characters of \fItemplate\fP were not XXXXXX;
 159 now \fItemplate\fP is unchanged.
 160 .sp
 161 For
 162 .BR mkstemps ()
 163 and
 164 .BR mkostemps ()
 165 .I template
 166 is less than
 167 .I "(6 + suffixlen)"
 168 characters long, or the last 6 characters before the suffix in
 169 .I template
 170 were not XXXXXX.
 171 .PP
 172 These functions may also fail with any of the errors described for
 173 .BR open (2).
 174 .SH VERSIONS
 175 .BR mkostemp ()
 176 is available since glibc 2.7.
 177 .BR mkstemps ()
 178 and
 179 .BR mkostemps ()
 180 are available since glibc 2.11.
 181 .SH "CONFORMING TO"
 182 .BR mkstemp ():
 183 4.3BSD, POSIX.1-2001.
 184
 185 .BR mkstemps ():
 186 unstandardized, but appears on several other systems.
 187 .\" mkstemps() appears to be at least on the BSDs, Mac OS X, Solaris,
 188 .\" and Tru64.
 189
 190 .BR mkostemp ()
 191 and
 192 .BR mkostemps ():
 193 are glibc extensions.
 194 .SH NOTES
 195 The old behavior of creating a file with mode 0666 may be
 196 a security risk, especially since other Unix flavors use 0600,
 197 and somebody might overlook this detail when porting programs.
 198
 199 More generally, the POSIX specification of
 200 .BR mkstemp ()
 201 does not say anything
 202 about file modes, so the application should make sure its
 203 file mode creation mask (see
 204 .BR umask (2))
 205 is set appropriately before calling
 206 .BR mkstemp ()
 207 (and
 208 .BR mkostemp ()).
 209
 210 The prototype for
 211 .BR mktemp ()
 212 is in
 213 .I <unistd.h>
 214 for libc4, libc5, glibc1; glibc2 follows POSIX.1 and has the prototype in
 215 .IR <stdlib.h> .
 216 .SH "SEE ALSO"
 217 .BR mkdtemp (3),
 218 .BR mktemp (3),
 219 .BR tempnam (3),
 220 .BR tmpfile (3),
 221 .BR tmpnam (3)