Linux: /tmp cleanup frequency

kerberos is working well in my laptop. However, since the temp ticket file krb5*** is stored in /tmp which is cleaned up as reboot, I cannot use kinit -R to renew the ticket-granting ticket even within its renewable life. So what I do is to change /tmp cleanup frequency. How? edit the file:

/etc/default/rcS

and check the default value of "TMPTIME", 0 means cleanup as reboot. TMPTIME=14 means that the files in the directory will be deleted in a frequency of 2 weeks.