ZDNet's LDP Mirror Linux Network Administrators Guide Prev Chapter 8. If your PPP setup doesn't work right away, you should look in this log file. If the log messages don't help, you can also turn on extra debugging output using the debug option. This output makes pppd log the contents of all control packets sent or received to syslog .
All messages then go to the daemon facility.
Finally, the most drastic way to check a problem is to enable kernel-level debugging by invoking pppd with the kdebug option.