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Signals are used internally by the implementation.
On Linux 2.2 and later, the first three real-time signals are used.
-On older Linux kernels, SIGUSR1 and SIGUSR2 are used.
+On older Linux kernels,
+.B SIGUSR1
+and
+.B SIGUSR2
+are used.
Applications must avoid the use of whichever set of signals is
employed by the implementation.
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