+The path to a file listing the hosts to ping. This file can be in the
+format used by \fI/etc/hosts\fP, or it can be any file that has host
+names as the first element on each line. If you use ssh, try this:
+.EX
+sonar -mode ping -ping-file $HOME/.ssh/known_hosts
+.EE
+This is used only used when \fIpingSource\fP is set to \fBfile\fP.