The exec Option

The exec option invokes a command or shell script when a link is brought up or taken down. Exec can be used on the link's calling or answering end and the command or shell script is executed immediately when the link changes state.

The first argument of the command or shell script invoked by exec is either "up" or "down." The second argument is the peer's IP address. Exec's third and subsequent arguments are those with which pppd was invoked.




	NOTE: Note: `pppd` runs suid root and anything specified in the Exec script is run as root. This can be a risk if mismanaged. Take appropriate security precautions with the exec script so it cannot be modified by non-root users.

Parent Environment and Session Variables

The entire parent environment is exported to exec scripts (the environment when pppd was invoked.) You should attempt to make the environment as small as possible because the environment will take up space for each pppd that is running. The exec script may also include variables that describe the current session. These variables include:

Variable	Description
PPPHOME	As you would expect, but always set.
PPP_COMMANDLINE	All arguments from the original command line.
PPP_LOCALADDR	Local address of link while up (negotiated).
PPP_REMOTEADDR	Remote address while up.
PPP_NETMASK	Netmask while up.
PPP_ORIG_LOCALADDR	Original local address (from command line).
PPP_ORIG_REMOTEADDR	Original remote address.
PPP_ORIG_NETMASK	Original netmask.
PPP_INTERFACE	Name of PPP interface (DUX).
PPP_DEVICE	Name of device being used for serial stream.
PPP_LOGFILE	Self-explanatory.
PPP_ACCTFILE	Self-explanatory.
PPP_AUTHNAME	Peer name if CHAP/PAP is used, else "name" parameter from command line, if given. Else user name of user that started pppd.
PPP_PID	pppd user process PID.
PPP_SHUTDOWN	Shutdown reason if link is going down and a shutdown reason is available, else non-existent.

Example

This example uses a Login shell script to invoke an executable shell script called $PPPHOME/Exec. $PPPHOME/Exec causes sendmail to run its queue whenever a remote system establishes a connection, possibly triggering a delivery to the remote system.

Login Shell Script

#!/bin/sh
PATH=/usr/bin:/usr/etc:/etc:/bin 
PPPHOME=/etc/ppp 
export PPPHOME PATH
 
mesg n 
stty -tostop 
exec   pppd   'hostname':   idle   130   exec $PPPHOME/Exec

Executable Shell Script:

#!/bin/sh
case "$1" in
    up)     echo   link is up at 'date' >   /dev/console ;
            /usr/lib/sendmail -q < /dev/null ;;
    down)   echo   link is down at 'date' >   /dev/console ;;
esac

The exec Option

Technical documentation

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Parent Environment and Session Variables

Example

Login Shell Script

Executable Shell Script: