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I got an embedded system trying to create a ppp connection using a GSM modem. However the connection is never established and all I get is this error message in syslog:

Oct 12 08:38:48 pppd[451]: pppd 2.4.4 started by root, uid 0
Oct 12 08:38:59 pppd[451]: Connect script failed
Oct 12 08:39:00 pppd[451]: Exit.

I now need some hints how to proceed finding the cause of this problem. Where should I start looking?

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up vote 4 down vote accepted

Somewhere in your ppp setup (probably either in /etc/ppp/options or at the command line), you have an option called connect followed by a command used to setup the modem for a connection. It's usually a chat script. You need to find out why that command is failing. If it is a chat script, you can make it verbose by changing it from chat blah blah... to chat -v blah blah.

Also for convenience, I like to add either the updetach or nodetach option to ppp so I don't have to keep checking the log.

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Great! I will try it out. – ihatetoregister Oct 14 '11 at 13:49
Found the problem! The bit rate setting of the modem and the port were not the same. – ihatetoregister Oct 18 '11 at 11:08
@ihatetoregister Interesting; I know at least one of the modem drivers specifically discards the bit rate, and I've tried setting various bit rates on many modems an not found it to affect anything. Would you mind sharing which modem this was? – Shawn J. Goff Oct 18 '11 at 11:19

Add the debug parameter, then you are able to see errors in logfile. If the error happens near authentication, then you probably use wrong authentication methods (most common case); if it happens near compression then you have forced something that isn't allowed by server.

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