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28 .\" @(#)mktemp.3 8.1 (Berkeley) 6/4/93
29 .\" $FreeBSD: src/lib/libc/stdio/mktemp.3,v 1.22 2007/01/09 00:28:07 imp Exp $
30 .\" $DragonFly: src/lib/libc/stdio/mktemp.3,v 1.3 2006/02/17 19:35:06 swildner Exp $
37 .Nd make temporary file name (unique)
43 .Fn mktemp "char *template"
45 .Fn mkstemp "char *template"
47 .Fn mkstemps "char *template" "int suffixlen"
49 .Fn mkdtemp "char *template"
54 takes the given file name template and overwrites a portion of it
55 to create a file name.
56 This file name is guaranteed not to exist at the time of function invocation
57 and is suitable for use
59 The template may be any file name with some number of
63 .Pa /tmp/temp.XXXXXX .
67 unique alphanumeric combination.
68 The number of unique file names
70 can return depends on the number of
77 selecting one of 56800235584 (62 ** 6) possible temporary file names.
82 makes the same replacement to the template and creates the template file,
83 mode 0600, returning a file descriptor opened for reading and writing.
84 This avoids the race between testing for a file's existence and opening it
89 function acts the same as
91 except it permits a suffix to exist in the template.
92 The template should be of the form
93 .Pa /tmp/tmpXXXXXXsuffix .
97 is told the length of the suffix string.
101 function makes the same replacement to the template as in
103 and creates the template directory, mode 0700.
109 functions return a pointer to the template on success and
117 return \-1 if no suitable file could be created.
118 If either call fails an error code is placed in the global variable
129 to one of the following values:
132 The pathname portion of the template is not an existing directory.
143 to any value specified by the
154 to any value specified by the
163 to any value specified by the
167 A common problem that results in a core dump is that the programmer
168 passes in a read-only string to
174 This is common with programs that were developed before
176 compilers were common.
180 .Qq /tmp/tempfile.XXXXXX
181 will result in a core dump due to
183 attempting to modify the string constant that was given.
184 If the program in question makes heavy use of that type
185 of function call, you do have the option of compiling the program
186 so that it will store string constants in a writable segment of memory.
189 for more information.
207 function first appeared in
213 function first appeared in
218 This family of functions produces filenames which can be guessed,
219 though the risk is minimized when large numbers of
222 increase the number of possible temporary filenames.
223 This makes the race in
225 between testing for a file's existence (in the
228 and opening it for use
229 (later in the user application)
230 particularly dangerous from a security perspective.
231 Whenever it is possible,
233 should be used instead, since it does not have the race condition.
236 cannot be used, the filename created by
238 should be created using the
242 and the return status of the call should be tested for failure.
243 This will ensure that the program does not continue blindly
244 in the event that an attacker has already created the file
245 with the intention of manipulating or reading its contents.
247 The implementation of these functions calls
249 which is not reentrant.
250 You must provide your own locking around this and other consumers of the