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32 .\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
40 .Nd make temporary file name (unique)
46 .Fn mktemp "char *template"
48 .Fn mkstemp "char *template"
50 .Fn mkstemps "char *template" "int suffixlen"
52 .Fn mkdtemp "char *template"
57 takes the given file name template and overwrites a portion of it
58 to create a file name.
59 This file name is guaranteed not to exist at the time of function invocation
60 and is suitable for use
62 The template may be any file name with some number of
66 .Pa /tmp/temp.XXXXXX .
70 unique alphanumeric combination.
71 The number of unique file names
73 can return depends on the number of
80 selecting one of 56800235584 (62 ** 6) possible temporary file names.
85 makes the same replacement to the template and creates the template file,
86 mode 0600, returning a file descriptor opened for reading and writing.
87 This avoids the race between testing for a file's existence and opening it
92 function acts the same as
94 except it permits a suffix to exist in the template.
95 The template should be of the form
96 .Pa /tmp/tmpXXXXXXsuffix .
100 is told the length of the suffix string.
104 function makes the same replacement to the template as in
106 and creates the template directory, mode 0700.
112 functions return a pointer to the template on success and
120 return \-1 if no suitable file could be created.
121 If either call fails an error code is placed in the global variable
132 to one of the following values:
135 The pathname portion of the template is not an existing directory.
146 to any value specified by the
157 to any value specified by the
166 to any value specified by the
170 A common problem that results in a core dump is that the programmer
171 passes in a read-only string to
177 This is common with programs that were developed before
179 compilers were common.
183 .Qq /tmp/tempfile.XXXXXX
184 will result in a core dump due to
186 attempting to modify the string constant that was given.
187 If the program in question makes heavy use of that type
188 of function call, you do have the option of compiling the program
189 so that it will store string constants in a writable segment of memory.
192 for more information.
210 function first appeared in
216 function first appeared in
221 This family of functions produces filenames which can be guessed,
222 though the risk is minimized when large numbers of
225 increase the number of possible temporary filenames.
226 This makes the race in
228 between testing for a file's existence (in the
231 and opening it for use
232 (later in the user application)
233 particularly dangerous from a security perspective.
234 Whenever it is possible,
236 should be used instead, since it does not have the race condition.
239 cannot be used, the filename created by
241 should be created using the
245 and the return status of the call should be tested for failure.
246 This will ensure that the program does not continue blindly
247 in the event that an attacker has already created the file
248 with the intention of manipulating or reading its contents.
250 The implementation of these functions calls
252 which is not reentrant.
253 You must provide your own locking around this and other consumers of the