stop the services which it use tmp directory
service httpd stop
service mysql stop
/etc/init.d/chkservd stop
then clean the tmp directory and create
/bin/umount -1 / tmp
/bin/umount -1 /war/tmp
/bin/rm -fv /usr/tmpDSK
/scripts/securetmp
Then start the services which you stop
service mysql start
service httpd start
/etc/init.d/chkservd restart
Source: http://www.cpanelim.net/lessons/cleaning-the-tmp-directory-on-linmux.html