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28 .\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
36 .Nd make temporary file name (unique)
42 .Fn mktemp "char *template"
44 .Fn mkstemp "char *template"
46 .Fn mkstemps "char *template" "int suffixlen"
48 .Fn mkdtemp "char *template"
53 takes the given file name template and overwrites a portion of it
54 to create a file name.
55 This file name is guaranteed not to exist at the time of function invocation
56 and is suitable for use
58 The template may be any file name with some number of
62 .Pa /tmp/temp.XXXXXX .
66 unique alphanumeric combination.
67 The number of unique file names
69 can return depends on the number of
76 selecting one of 56800235584 (62 ** 6) possible temporary file names.
81 makes the same replacement to the template and creates the template file,
82 mode 0600, returning a file descriptor opened for reading and writing.
83 This avoids the race between testing for a file's existence and opening it
88 function acts the same as
90 except it permits a suffix to exist in the template.
91 The template should be of the form
92 .Pa /tmp/tmpXXXXXXsuffix .
96 is told the length of the suffix string.
100 function makes the same replacement to the template as in
102 and creates the template directory, mode 0700.
108 functions return a pointer to the template on success and
116 return \-1 if no suitable file could be created.
117 If either call fails an error code is placed in the global variable
128 to one of the following values:
131 The pathname portion of the template is not an existing directory.
142 to any value specified by the
153 to any value specified by the
162 to any value specified by the
166 A common problem that results in a core dump is that the programmer
167 passes in a read-only string to
173 This is common with programs that were developed before
175 compilers were common.
179 .Qq /tmp/tempfile.XXXXXX
180 will result in a core dump due to
182 attempting to modify the string constant that was given.
183 If the program in question makes heavy use of that type
184 of function call, you do have the option of compiling the program
185 so that it will store string constants in a writable segment of memory.
188 for more information.
206 function first appeared in
212 function first appeared in
217 This family of functions produces filenames which can be guessed,
218 though the risk is minimized when large numbers of
221 increase the number of possible temporary filenames.
222 This makes the race in
224 between testing for a file's existence (in the
227 and opening it for use
228 (later in the user application)
229 particularly dangerous from a security perspective.
230 Whenever it is possible,
232 should be used instead, since it does not have the race condition.
235 cannot be used, the filename created by
237 should be created using the
241 and the return status of the call should be tested for failure.
242 This will ensure that the program does not continue blindly
243 in the event that an attacker has already created the file
244 with the intention of manipulating or reading its contents.
246 The implementation of these functions calls
248 which is not reentrant.
249 You must provide your own locking around this and other consumers of the