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From: Terry Lambert <tlambert@primenet.com>
Message-Id: <199803070058.RAA24995@usr09.primenet.com>
Subject: Re: Detecting state of PPP
To: bhlewis@gte.net (Benjamin Lewis)
Date: Sat, 7 Mar 1998 00:58:46 +0000 (GMT)
Cc: pvh@leftside.wcape.school.za, freebsd-hackers@FreeBSD.ORG
In-Reply-To: <199803060014.TAA13234@gte.net> from "Benjamin Lewis" at Mar 5, 98 07:14:00 pm
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> > How does one go about writing a program to check if a PPP link is up
> > or down? 
> 
> I've seen lots of complicated responses to this, so there is probably 
> something inherintly wrong with what I've always done, check for the
> existence of the /var/spool/lock/LCK..cuaa? file.  If there is a possibility
> that something else is using the serial line, one could check whether the
> PID in the file matches the PPP process.

#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <stdio.h>

main() {
	char		*ppp_name = "tun0";
	struct ifreq	ifr;
	int		s;

	if( ( s = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
		perror( "socket");
		exit( 1);
	}

	strcpy( ifr.ifr_name,ppp_name);
	if (ioctl(s, SIOCGIFFLAGS, (caddr_t)&ifr) == -1) {
		perror( "ioctl");
		exit( 1);
	}

	printf( "%s: %s\n", ppp_name, (ifr.ifs_flags & IFF_UP) ? "up" : "down");

	exit( 0);
}


Of course, not all of the includes are needed; I ripped this out of an
experimental piece of DHCP code.

Change the interface name from "tun0" to whatever; I happen to run user
space ppp, so mine is named tun0.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

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