История изменений

The Linux kernel supports a range of 33 different real-time
       signals, numbered 32 to 64.  However, the glibc POSIX threads
       implementation internally uses two (for NPTL) or three (for
       LinuxThreads) real-time signals (see pthreads(7)), and adjusts
       the value of SIGRTMIN suitably (to 34 or 35).  Because the range
       of available real-time signals varies according to the glibc
       threading implementation (and this variation can occur at run
       time according to the available kernel and glibc), and indeed the
       range of real-time signals varies across UNIX systems, programs
       should never refer to real-time signals using hard-coded numbers,
       but instead should always refer to real-time signals using the
       notation SIGRTMIN+n, and include suitable (run-time) checks that
       SIGRTMIN+n does not exceed SIGRTMAX.

The Linux kernel supports a range of 33 different real-time
       signals, numbered 32 to 64.  However, the glibc POSIX threads
       implementation internally uses two (for NPTL) or three (for
       LinuxThreads) real-time signals (see pthreads(7)), and adjusts
       the value of SIGRTMIN suitably (to 34 or 35).  Because the range
       of available real-time signals varies according to the glibc
       threading implementation (and this variation can occur at run
       time according to the available kernel and glibc), and indeed the
       range of real-time signals varies across UNIX systems, programs
       should never refer to real-time signals using hard-coded numbers,
       but instead should always refer to real-time signals using the
       notation SIGRTMIN+n, and include suitable (run-time) checks that
       SIGRTMIN+n does not exceed SIGRTMAX.