mktemp, mkstemp, mkdtemp - make unique temporary file or directory name
Standard C Library (libc, -lc)
The mktemp() function takes the given file name template and overwrites a
portion of it to create a file name. This file name is unique and suitable
for use by the application. The template may be any file name with
some number of `Xs' appended to it, for example /tmp/temp.XXXX. The
trailing `Xs' are replaced with the current process number and/or a
unique letter combination. The number of unique file names mktemp() can
return depends on the number of `Xs' provided; six `Xs' will result in
mktemp() testing roughly 26 ** 6 combinations.
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 mkdtemp() function is similar to mkstemp(), but it creates a mode
0700 directory instead and returns the path.
Please note that the permissions of the file or directory being created
are subject to the restrictions imposed by the umask(2) system call. It
may thus happen that the created file is unreadable and/or unwritable.
The mktemp() and mkdtemp() functions return a pointer to the template on
success and NULL on failure. The mkstemp() function returns -1 if no
suitable file could be created. If either call fails an error code is
placed in the global variable errno.
The mktemp(), mkstemp() and mkdtemp() functions may set errno to one of
the following values:
[ENOTDIR] The pathname portion of the template is not an existing
The mktemp(), mkstemp() and mkdtemp() functions may also set errno to any
value specified by the stat(2) function.
The mkstemp() function may also set errno to any value specified by the
The mkdtemp() function may also set errno to any value specified by the
chmod(2), getpid(2), open(2), stat(2), umask(2)
A mktemp() function appeared in Version 7 AT&T UNIX.
The mkstemp() function appeared in 4.4BSD.
The mkdtemp() function appeared in NetBSD 1.4.
SECURITY CONSIDERATIONS [Toc] [Back]
The use of mktemp() should generally be avoided, as a hostile process can
exploit a race condition in the time between the generation of a temporary
filename by mktemp() and the invoker's use of the temporary name. A
link-time warning will be issued advising the use of mkstemp() or
BSD July 28, 1998 BSD
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