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Signals

Although we listed them as a method of IPC in the previous section, signals are more usually employed in a wide range of other contexts, and so deserve a longer discussion.

Signals are often described as “software interrupts.” The arrival of a signal informs a process that some event or exceptional condition has occurred. There are various types of signals, each of which identifies a different event or condition. Each signal type is identified by a different integer, defined with symbolic names of the form SIGxxxx.

Signals are sent to a process by the kernel, by another process (with suitable permissions), or by the process itself. For example, the kernel may send a signal to a process when one of the following occurs:


  

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