runlevel 6 is reboot, runlevel 0 is shutdown
P.S. Oooops, sorry wrong forum - slackware is BSD init'ed, not SysV. It is all the way around 0 is halt and 6 is reboot, let's see....
Ignore Ooops, and BSD vs SysV - they are both still using 0 and 6 for halt and reboot respectively