Using Options Files Linux Network Administrators Guide Prev Chapter 8. Before pppd parses its command-line arguments, it scans several files for default options. These files may contain any valid command-line arguments spread out across an arbitrary number of lines.
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Using it to set some global defaults is a good idea, because it allows you to keep your users from doing several things that may compromise security. This option cannot be overridden by the user, so it becomes impossible to establish a PPP connection with any system that is not in your authentication databases. It allows each user to specify her own set of default options. The next three options relate to authentication and, therefore, to system security.