The pppd daemon parses the following:
pppd scans the command line to determine the device in use. The daemon does not yet interpret any options that are encountered.
pppd tries to discover the serial device to use by using these criteria:
If a serial device is specified on the command line, or a previously processed configuration file, pppd uses the name of that device.
If no serial device is named, then pppd searches for the notty, pty, or socket option on the command line. If one of these options is specified, pppd assumes that no device name exists.
Otherwise, if pppd discovers that standard input is attached to a tty, then the name of the tty is used.
If pppd still cannot find a serial device, pppd terminates the connection and issues an error.
pppd then checks for the existence of the /etc/ppp/options.ttyname file. If the file is found, pppd parses the file.
pppd processes any options on the command line.
pppd negotiates the Link Control Protocol (LCP) to set up the link.
(Optional) If authentication is required, pppd reads /etc/ppp/pap-secrets or /etc/ppp/chap-secrets to authenticate the opposite peer.
The file /etc/ppp/peers/peer-name is read when the pppd daemon encounters the option call peer-name on the command line or in the other configuration files.