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### 24.7 Blocking Signals

Blocking a signal means telling the operating system to hold it and deliver it later. Generally, a program does not block signals indefinitely—it might as well ignore them by setting their actions to `SIG_IGN`. But it is useful to block signals briefly, to prevent them from interrupting sensitive operations. For instance:

- You can use the `sigprocmask` function to block signals while you modify global variables that are also modified by the handlers for these signals.
- You can set `sa_mask` in your `sigaction` call to block certain signals while a particular signal handler runs. This way, the signal handler can run without being interrupted itself by signals.