Согласно signal(7) manpage , есть несколько отличий:
Real-time signals are distinguished by the following:
1. Multiple instances of real-time signals can be queued. By con-
trast, if multiple instances of a standard signal are delivered
while that signal is currently blocked, then only one instance is
queued.
2. If the signal is sent using sigqueue(2), an accompanying value
(either an integer or a pointer) can be sent with the signal. If
the receiving process establishes a handler for this signal using
the SA_SIGINFO flag to sigaction(2) then it can obtain this data
via the si_value field of the siginfo_t structure passed as the
second argument to the handler. Furthermore, the si_pid and si_uid
fields of this structure can be used to obtain the PID and real
user ID of the process sending the signal.
3. Real-time signals are delivered in a guaranteed order. Multiple
real-time signals of the same type are delivered in the order they
were sent. If different real-time signals are sent to a process,
they are delivered starting with the lowest-numbered signal.
(I.e., low-numbered signals have highest priority.)
If both standard and real-time signals are pending for a process, POSIX
leaves it unspecified which is delivered first. Linux, like many other
implementations, gives priority to standard signals in this case.