Recall the output of the kill -l (l for list) command; the platform's supported signals are displayed—numeric integer and symbolic name, both. The first 31 signals are the standard or Unix signals (seen in Chapter 11, Signaling - Part I, The standard or Unix signals section); we have been working with them quite a bit now.
Signal numbers 34 to 64 all start with SIGRT—SIGRTMIN to SIGRTMAX—they are called the real time signals:
$ kill -l |grep "SIGRT"
31)SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38)SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43)SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48)SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX...