Forgot to add

docs/linuxex/ex58.pp

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+Program example58;
+
+{ Program to demonstrate the Signal function.}
+
+{ 
+do a kill -USR1 pid from another terminal to see what happens.
+replace pid with the real pid of this program. 
+You can get this pid by running 'ps'.
+}
+
+uses Linux;
+
+Procedure DoSig(sig : Longint);cdecl;
+
+begin
+   writeln('Receiving signal: ',sig);
+end; 
+
+begin
+   SigNal(SigUsr1,@DoSig);
+   if LinuxError<>0 then
+     begin
+     writeln('Error: ',linuxerror,'.');
+     halt(1);
+     end;
+   Writeln ('Send USR1 signal or press <ENTER> to exit'); 
+   readln;
+end.