Installing and Administering PPP

140 Chapter 6
Troubleshooting pppd
Scenario: When you telnet to test if the answering PPP account is set up correctly,
you are greeted with what looks like line noise. This is the PPP Link
control Protocol Configure-Request packet, but it takes a long time for
pppd to give up and go away.
Solution: The easy way to instruct the answering pppd to exit and close the
connection is to type the four-character sequence of a tilde (~), followed
by three control-Cs.
The ’~^C^C^C’ sequence only works in PPP mode, not in SLIP mode.
And in PPP mode, if you specified ‘passive’ on the command line,
‘~^C^C^C’ only works after receipt of a good PPP packet.
Scenario: pppd will not dial out; the log file says ‘Device is locked.’
Solution: pppd uses lock files compatible with other programs to avoid using a
device already in use by another program, and to keep other programs
from interfering with devices in use by pppd. If the pppd.log file says
‘Device is locked,’ look for a lock file such as LCK..cua in /usr/spool/locks,
/usr/spool/uucp, /usr/spool/uucp/LCK, /var/spool/locks, or wherever your
system keeps tty lock files. Each lock file should contain the process ID of
the owner process. If the lock file is four bytes long, the process ID is a
32-bit binary number. If the lock file is 11 bytes long, the process ID is
printed in ASCII. Look in the lock file for the owner PID (use od -d for
binary files and cat for ASCII lock files), and then use ps to look for the
owner.
When pppd finds a lock file of zero length, it has no way of knowing the
PID of the process that created it, so to be safe, it gives up trying to open
the associated tty.
Scenario: Even though UUCP is using the modem, pppd tries to use it to place an
outbound call. And when pppd has an active link, UUCP tries to make
an outbound call.
Solution: The outbound ‘Auto Call Unit’ (ACU) names used in PPP’s Devices must
match the names used for similar purposes in UUCP’s Devices file. For
example, if your UUCP configuration knows a device as cua0, but PPP
knows it as cua, each facility will be unable to discover the lock file
indicating that the other is using the device.