Add the following lines to /etc/security/limits.conf (before the "#End of file" line, needs root access):
@realtime - rtprio 99
@realtime - memlock unlimited
Create the realtime group and add yourself to it:
groupadd realtime
usermod -a -G realtime <YourUserName>
Further reading: http://www.jackaudio.org/faq/linux_rt_config.html