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28 .\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
35 .Nd make temporary file name (unique)
41 .Fn mktemp "char *template"
43 .Fn mkstemp "char *template"
45 .Fn mkostemp "char *template" "int oflags"
47 .Fn mkostemps "char *template" "int suffixlen" "int oflags"
49 .Fn mkostempsat "int dfd" "char *template" "int suffixlen" "int oflags"
51 .Fn mkdtemp "char *template"
54 .Fn mkstemps "char *template" "int suffixlen"
59 takes the given file name template and overwrites a portion of it
60 to create a file name.
61 This file name is guaranteed not to exist at the time of function invocation
62 and is suitable for use
64 The template may be any file name with some number of
68 .Pa /tmp/temp.XXXXXX .
72 unique alphanumeric combination.
73 The number of unique file names
75 can return depends on the number of
82 selecting one of 56800235584 (62 ** 6) possible temporary file names.
87 makes the same replacement to the template and creates the template file,
88 mode 0600, returning a file descriptor opened for reading and writing.
89 This avoids the race between testing for a file's existence and opening it
97 but allows specifying additional
101 The permitted flags are
114 functions act the same as
119 except they permit a suffix to exist in the template.
120 The template should be of the form
121 .Pa /tmp/tmpXXXXXXsuffix .
127 are told the length of the suffix string.
131 function acts the same as
133 but takes an additional directory descriptor as a parameter.
134 The temporary file is created relative to the corresponding
135 directory, or to the current working directory if the special
139 If the template path is an absolute path, the
141 parameter is ignored and the behavior is identical to
146 function makes the same replacement to the template as in
148 and creates the template directory, mode 0700.
154 functions return a pointer to the template on success and
164 return \-1 if no suitable file could be created.
165 If either call fails an error code is placed in the global variable
178 to one of the following values:
181 The pathname portion of the template is not an existing directory.
191 to the following value:
209 to any value specified by the
222 to any value specified by the
231 to any value specified by the
235 A common problem that results in a core dump is that the programmer
236 passes in a read-only string to
242 This is common with programs that were developed before
244 compilers were common.
248 .Qq /tmp/tempfile.XXXXXX
249 will result in a core dump due to
251 attempting to modify the string constant that was given.
258 function prototypes are also available from
271 functions are expected to conform to
275 function is expected to conform to
277 and is not specified by
285 functions do not conform to any standard.
297 function first appeared in
303 function first appeared in
311 functions appeared in
318 This family of functions produces filenames which can be guessed,
319 though the risk is minimized when large numbers of
322 increase the number of possible temporary filenames.
323 This makes the race in
325 between testing for a file's existence (in the
328 and opening it for use
329 (later in the user application)
330 particularly dangerous from a security perspective.
331 Whenever it is possible,
336 should be used instead, since they do not have the race condition.
339 cannot be used, the filename created by
341 should be created using the
345 and the return status of the call should be tested for failure.
346 This will ensure that the program does not continue blindly
347 in the event that an attacker has already created the file
348 with the intention of manipulating or reading its contents.