ns_mktemp returns a unique filename based on the template you specify. ns_tmpnam returns a filename that can safely be used for a temporary file.
The template for ns_mktemp should contain a string with six trailing Xs, which will be replaced with an alpha-numeric string of six characters chosen to make the filename unique. If template does not end with six trailing Xs the empty string will be returned.
ns_tmpnam calls the tmpnam() C library function, and the results will depend on your operating system. On Irix, for example, tmpnam() always generate a file name using the path-prefix defined as P_tmpdir in the header file which is "/var/tmp/".
nscp> ns_tmpnam ;# On Linux
nscp> ns_mktemp /tmp/foobar.XXXXXX