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28 .\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
29 .\" $FreeBSD: head/lib/libc/stdio/mktemp.3 254151 2013-08-09 17:24:23Z jilles $
36 .Nd make temporary file name (unique)
42 .Fn mktemp "char *template"
44 .Fn mkstemp "char *template"
46 .Fn mkostemp "char *template" "int oflags"
48 .Fn mkostemps "char *template" "int suffixlen" "int oflags"
50 .Fn mkdtemp "char *template"
53 .Fn mkstemps "char *template" "int suffixlen"
58 takes the given file name template and overwrites a portion of it
59 to create a file name.
60 This file name is guaranteed not to exist at the time of function invocation
61 and is suitable for use
63 The template may be any file name with some number of
67 .Pa /tmp/temp.XXXXXX .
71 unique alphanumeric combination.
72 The number of unique file names
74 can return depends on the number of
81 selecting one of 56800235584 (62 ** 6) possible temporary file names.
86 makes the same replacement to the template and creates the template file,
87 mode 0600, returning a file descriptor opened for reading and writing.
88 This avoids the race between testing for a file's existence and opening it
95 but allows specifying additional
99 The permitted flags are
112 functions act the same as
117 except they permit a suffix to exist in the template.
118 The template should be of the form
119 .Pa /tmp/tmpXXXXXXsuffix .
125 are told the length of the suffix string.
131 but allows specifying additional
138 function makes the same replacement to the template as in
140 and creates the template directory, mode 0700.
146 functions return a pointer to the template on success and
156 return \-1 if no suitable file could be created.
157 If either call fails an error code is placed in the global variable
170 to one of the following values:
173 The pathname portion of the template is not an existing directory.
183 to the following value:
201 to any value specified by the
214 to any value specified by the
223 to any value specified by the
227 A common problem that results in a core dump is that the programmer
228 passes in a read-only string to
234 This is common with programs that were developed before
236 compilers were common.
240 .Qq /tmp/tempfile.XXXXXX
241 will result in a core dump due to
243 attempting to modify the string constant that was given.
250 function prototypes are also available from
263 functions are expected to conform to
267 function is expected to conform to
269 and is not specified by
282 function first appeared in
288 function first appeared in
296 functions appeared in
301 This family of functions produces filenames which can be guessed,
302 though the risk is minimized when large numbers of
305 increase the number of possible temporary filenames.
306 This makes the race in
308 between testing for a file's existence (in the
311 and opening it for use
312 (later in the user application)
313 particularly dangerous from a security perspective.
314 Whenever it is possible,
318 should be used instead, since it does not have the race condition.
321 cannot be used, the filename created by
323 should be created using the
327 and the return status of the call should be tested for failure.
328 This will ensure that the program does not continue blindly
329 in the event that an attacker has already created the file
330 with the intention of manipulating or reading its contents.