Chapter 9. Signals
Signals were introduced by the first Unix systems to simplify interprocess communication. The kernel also uses them to notify processes of system events. In contrast to interrupts and exceptions, most signals are visible to User Mode processes.
Signals have been around for 30 years with only minor changes. Due to their relative simplicity and efficiency, they continue to be widely used, although as we shall see in Chapter 18, other higher-level tools have been introduced for the same purpose.
The first sections of this chapter examine in detail how signals are handled by the Linux kernel, then we discuss the system calls that allow processes to exchange signals.
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