mkstemp(3c) [opensolaris man page]
mkstemp(3C) Standard C Library Functions mkstemp(3C) NAME
mkstemp, mkstemps, mkdtemp - make a unique file name from a template and open the file SYNOPSIS
#include <stdlib.h> int mkstemp(char *template); int mkstemps(char *template, int slen); char *mkdtemp(char *template); DESCRIPTION
The mkstemp() function replaces the contents of the string pointed to by template by a unique file name, and returns a file descriptor for the file open for reading and writing. The function thus prevents any possible race condition between testing whether the file exists and opening it for use. The string in template should look like a file name with six trailing 'X's; mkstemp() replaces each 'X' with a charac- ter from the portable file name character set. The characters are chosen such that the resulting name does not duplicate the name of an existing file. The mkstemps() function behaves the same as mkstemp(), except it permits a suffix to exist in the template. The template should be of the form /tmp/tmpXXXXXXsuffix. The slen parameter specifies the length of the suffix string. The mkdtemp() function makes the same replacement to the template as in mktemp(3C) and creates the template directory using mkdir(2), pass- ing a mode argument of 0700. RETURN VALUES
Upon successful completion, mkstemp() returns an open file descriptor. Otherwise -1 is returned if no suitable file could be created. ERRORS
The mkstemp(), mkstemps(), and mkdtemp() functions can set errno to the same values as lstat(2). The mkstemp() and mkstemps() functions can set errno to the same values as open(2). The mkdtemp() function can set errno to the same values as mkdir(2). USAGE
It is possible to run out of letters. The mkstemp() function does not check to determine whether the file name part of template exceeds the maximum allowable file name length. The tmpfile(3C) function is preferred over this function. The mkstemp() function is frequently used to create a temporary file that will be removed by the application before the application termi- nates. The mkstemp() function has a transitional interface for 64-bit file offsets. See lf64(5). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ |ATTRIBUTE TYPE |ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |See below. | +-----------------------------+-----------------------------+ The mkstemp() function is Standard. The mkstemps() and mkdtemp() functions are Stable. SEE ALSO
getpid(2), lstat(2), mkdir(2), open(2), tmpfile(3C), mktemp(3C), attributes(5), lf64(5), standards(5) SunOS 5.11 22 Feb 2006 mkstemp(3C)
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MKTEMP(3) BSD Library Functions Manual MKTEMP(3) NAME
mkdtemp, mkstemp, mkstemps, mktemp -- make temporary file name (unique) LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> char * mkdtemp(char *template); int mkstemps(char *template, int suffixlen); #include <stdlib.h> int mkstemp(char *template); char * mktemp(char *template); DESCRIPTION
The mktemp() function takes the given file name template and overwrites a portion of it to create a file name. This file name is guaranteed not to exist at the time of function invocation and is suitable for use by the application. The template may be any file name with some num- ber of 'Xs' appended to it, for example /tmp/temp.XXXXXX. The trailing 'Xs' are replaced with a unique alphanumeric combination. The number of unique file names mktemp() can return depends on the number of 'Xs' provided; six 'Xs' will result in mktemp() selecting one of 56800235584 (62 ** 6) possible temporary file names. The mkstemp() function makes the same replacement to the template and creates the template file, mode 0600, returning a file descriptor opened for reading and writing. This avoids the race between testing for a file's existence and opening it for use. The mkstemps() function acts the same as mkstemp(), except it permits a suffix to exist in the template. The template should be of the form /tmp/tmpXXXXXXsuffix. The mkstemps() function is told the length of the suffix string. The mkdtemp() function makes the same replacement to the template as in mktemp() and creates the template directory, mode 0700. RETURN VALUES
The mktemp() and mkdtemp() functions return a pointer to the template on success and NULL on failure. The mkstemp() and mkstemps() functions return -1 if no suitable file could be created. If either call fails an error code is placed in the global variable errno. ERRORS
The mkstemp(), mkstemps() and mkdtemp() functions may set errno to one of the following values: [ENOTDIR] The pathname portion of the template is not an existing directory. The mkstemp(), mkstemps(), and mkdtemp() functions may also set errno to any value specified by the stat(2) function. The mkstemp() and mkstemps() functions may also set errno to any value specified by the open(2) function. The mkdtemp() function may also set errno to any value specified by the mkdir(2) function. NOTES
A common problem that results in a core dump is that the programmer passes in a read-only string to mktemp(), mkstemp(), mkstemps(), or mkdtemp(). This is common with programs that were developed before ISO/IEC 9899:1990 (``ISO C90'') compilers were common. For example, calling mkstemp() with an argument of "/tmp/tempfile.XXXXXX" will result in a core dump due to mkstemp() attempting to modify the string con- stant that was given. If the program in question makes heavy use of that type of function call, you do have the option of compiling the pro- gram so that it will store string constants in a writable segment of memory. See gcc(1) for more information. LEGACY SYNOPSIS
#include <unistd.h> The include file <unistd.h> is necessary and sufficient for all functions. SEE ALSO
chmod(2), getpid(2), mkdir(2), open(2), stat(2), compat(5) HISTORY
A mktemp() function appeared in Version 7 AT&T UNIX. The mkstemp() function appeared in 4.4BSD. The mkdtemp() function first appeared in OpenBSD 2.2, and later in FreeBSD 3.2. The mkstemps() function first appeared in OpenBSD 2.4, and later in FreeBSD 3.4. BUGS
This family of functions produces filenames which can be guessed, though the risk is minimized when large numbers of 'Xs' are used to increase the number of possible temporary filenames. This makes the race in mktemp(), between testing for a file's existence (in the mktemp() function call) and opening it for use (later in the user application) particularly dangerous from a security perspective. Whenever it is possible, mkstemp() should be used instead, since it does not have the race condition. If mkstemp() cannot be used, the filename cre- ated by mktemp() should be created using the O_EXCL flag to open(2) and the return status of the call should be tested for failure. This will ensure that the program does not continue blindly in the event that an attacker has already created the file with the intention of manipulating or reading its contents. BSD
February 11, 1998 BSD