man3/mkstemp.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright (C) 2008, Michael Kerrisk <mtk.manpages@gmail.com>
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  25 .\"
  26 .\" References consulted:
  27 .\"     Linux libc source code
  28 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  29 .\"     386BSD man pages
  30 .\" Modified Sat Jul 24 18:48:48 1993 by Rik Faith (faith@cs.unc.edu)
  31 .\" Modified 980310, aeb
  32 .\" Modified 990328, aeb
  33 .\" 2008-06-19, mtk, Added mkostemp(); various other changes
  34 .\"
  35 .TH MKSTEMP 3  2016-10-08 "GNU" "Linux Programmer's Manual"
  36 .SH NAME
  37 mkstemp, mkostemp, mkstemps, mkostemps \- create a unique temporary file
  38 .SH SYNOPSIS
  39 .nf
  40 .B #include <stdlib.h>
  41 .sp
  42 .BI "int mkstemp(char *" template );
  43 .sp
  44 .BI "int mkostemp(char *" template ", int " flags );
  45 .sp
  46 .BI "int mkstemps(char *" template ", int " suffixlen );
  47 .sp
  48 .BI "int mkostemps(char *" template ", int " suffixlen ", int " flags );
  49 .fi
  50 .sp
  51 .in -4n
  52 Feature Test Macro Requirements for glibc (see
  53 .BR feature_test_macros (7)):
  54 .in
  55 .sp
  56 .BR mkstemp ():
  57 .ad l
  58 .RS 4
  59 .PD 0
  60 _XOPEN_SOURCE\ >=\ 500
  61 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  62     || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
  63     || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  64 .PD
  65 .RE
  66 .ad b
  67 .PP
  68 .BR mkostemp ():
  69 _GNU_SOURCE
  70 .br
  71 .BR mkstemps ():
  72     /* Glibc since 2.19: */ _DEFAULT_SOURCE
  73         || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  74 .br
  75 .BR mkostemps ():
  76 _GNU_SOURCE
  77 .SH DESCRIPTION
  78 The
  79 .BR mkstemp ()
  80 function generates a unique temporary filename from
  81 .IR template ,
  82 creates and opens the file,
  83 and returns an open file descriptor for the file.
  84
  85 The last six characters of
  86 .I template
  87 must be "XXXXXX" and these are replaced with a string that makes the
  88 filename unique.
  89 Since it will be modified,
  90 .I template
  91 must not be a string constant, but should be declared as a character array.
  92
  93 The file is created with
  94 permissions 0600, that is, read plus write for owner only.
  95 The returned file descriptor provides both read and write access to the file.
  96 The file is opened with the
  97 .BR open (2)
  98 .B O_EXCL
  99 flag, guaranteeing that the caller is the process that creates the file.
 100
 101 The
 102 .BR mkostemp ()
 103 function is like
 104 .BR mkstemp (),
 105 with the difference that the following bits\(emwith the same meaning as for
 106 .BR open (2)\(emmay
 107 be specified in
 108 .IR flags :
 109 .BR O_APPEND ,
 110 .BR O_CLOEXEC ,
 111 and
 112 .BR O_SYNC .
 113 Note that when creating the file,
 114 .BR mkostemp ()
 115 includes the values
 116 .BR O_RDWR ,
 117 .BR O_CREAT ,
 118 and
 119 .BR O_EXCL
 120 in the
 121 .I flags
 122 argument given to
 123 .BR open (2);
 124 including these values in the
 125 .I flags
 126 argument given to
 127 .BR mkostemp ()
 128 is unnecessary, and produces errors on some
 129 .\" Reportedly, FreeBSD
 130 systems.
 131
 132 The
 133 .BR mkstemps ()
 134 function is like
 135 .BR mkstemp (),
 136 except that the string in
 137 .I template
 138 contains a suffix of
 139 .I suffixlen
 140 characters.
 141 Thus,
 142 .I template
 143 is of the form
 144 .IR "prefixXXXXXXsuffix" ,
 145 and the string XXXXXX is modified as for
 146 .BR mkstemp ().
 147
 148 The
 149 .BR mkostemps ()
 150 function is to
 151 .BR mkstemps ()
 152 as
 153 .BR mkostemp ()
 154 is to
 155 .BR mkstemp ().
 156 .SH RETURN VALUE
 157 On success, these functions return the file descriptor
 158 of the temporary file.
 159 On error, \-1 is returned, and
 160 .I errno
 161 is set appropriately.
 162 .SH ERRORS
 163 .TP
 164 .B EEXIST
 165 Could not create a unique temporary filename.
 166 Now the contents of \fItemplate\fP are undefined.
 167 .TP
 168 .B EINVAL
 169 For
 170 .BR mkstemp ()
 171 and
 172 .BR mkostemp ():
 173 The last six characters of \fItemplate\fP were not XXXXXX;
 174 now \fItemplate\fP is unchanged.
 175 .sp
 176 For
 177 .BR mkstemps ()
 178 and
 179 .BR mkostemps ():
 180 .I template
 181 is less than
 182 .I "(6 + suffixlen)"
 183 characters long, or the last 6 characters before the suffix in
 184 .I template
 185 were not XXXXXX.
 186 .PP
 187 These functions may also fail with any of the errors described for
 188 .BR open (2).
 189 .SH VERSIONS
 190 .BR mkostemp ()
 191 is available since glibc 2.7.
 192 .BR mkstemps ()
 193 and
 194 .BR mkostemps ()
 195 are available since glibc 2.11.
 196 .SH ATTRIBUTES
 197 For an explanation of the terms used in this section, see
 198 .BR attributes (7).
 199 .TS
 200 allbox;
 201 lbw23 lb lb
 202 l l l.
 203 Interface       Attribute       Value
 204 T{
 205 .BR mkstemp (),
 206 .BR mkostemp (),
 207 .br
 208 .BR mkstemps (),
 209 .BR mkostemps ()
 210 T}      Thread safety   MT-Safe
 211 .TE
 212 .SH CONFORMING TO
 213 .BR mkstemp ():
 214 4.3BSD, POSIX.1-2001.
 215
 216 .BR mkstemps ():
 217 unstandardized, but appears on several other systems.
 218 .\" mkstemps() appears to be at least on the BSDs, Mac OS X, Solaris,
 219 .\" and Tru64.
 220
 221 .BR mkostemp ()
 222 and
 223 .BR mkostemps ():
 224 are glibc extensions.
 225 .SH NOTES
 226 In glibc versions 2.06 and earlier, the file is created with permissions 0666,
 227 that is, read and write for all users.
 228 This old behavior may be
 229 a security risk, especially since other UNIX flavors use 0600,
 230 and somebody might overlook this detail when porting programs.
 231 POSIX.1-2008 adds a requirement that the file be created with mode 0600.
 232
 233 More generally, the POSIX specification of
 234 .BR mkstemp ()
 235 does not say anything
 236 about file modes, so the application should make sure its
 237 file mode creation mask (see
 238 .BR umask (2))
 239 is set appropriately before calling
 240 .BR mkstemp ()
 241 (and
 242 .BR mkostemp ()).
 243 .\"
 244 .\" The prototype for
 245 .\" .BR mkstemp ()
 246 .\" is in
 247 .\" .I <unistd.h>
 248 .\" for libc4, libc5, glibc1; glibc2 follows POSIX.1 and has the prototype in
 249 .\" .IR <stdlib.h> .
 250 .SH SEE ALSO
 251 .BR mkdtemp (3),
 252 .BR mktemp (3),
 253 .BR tempnam (3),
 254 .BR tmpfile (3),
 255 .BR tmpnam (3)