SIGRTMIN

SIGRTMIN is the symbolic name for the lowest real-time signal number in POSIX-compliant systems. It marks the lower bound of the range of real-time signals, which on a given system run from SIGRTMIN through SIGRTMAX inclusive. The exact numeric values are implementation-defined and may vary by architecture and C library; the macros SIGRTMIN and SIGRTMAX are provided so programs can adapt to the system’s range.

Real-time signals differ from standard signals in that they are queued: multiple instances and multiple distinct real-time signals can be pending simultaneously. They are delivered in a defined order, typically from the lowest-numbered real-time signal upward, so lower-numbered real-time signals have higher priority. Real-time signals can carry accompanying data via the sigqueue interface or via the si_value payload when a signal is received with SA_SIGINFO.

Usage and semantics: Real-time signals are commonly employed for asynchronous notifications between processes or between threads within a process. They offer reliable delivery and the ability to queue information, making them suitable for time-sensitive IPC and event notification. They are delivered only when unblocked and can be handled by a signal handler installed with sigaction, using SA_SIGINFO to access any payload.

Notes: The range of real-time signals and the behavior of their queuing are defined by the system and C library; on different Unix-like systems the exact numbers may differ. See also SIGRTMAX, POSIX signals, sigqueue, and SA_SIGINFO for related concepts.