"Address already in use" error when OpenVPN is NOT running

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Tags:  openvpn, rant

So for the past week or so I’ve been trying to set up a dual-stack-payload OpenVPN server.  I was playing around with some IPv6 route settings earlier when it started doing this:

$ sudo openvpn /etc/openvpn/server.conf
Wed Aug 31 02:41:06 2011 Herp derp, herpity derp derp...
Wed Aug 31 02:41:06 2011 TCP/UDP: Socket bind failed on local
address [AF_INET] Address already in use
Wed Aug 31 02:41:06 2011 Exiting due to fatal error

$ echo "OH FUCK WHY WONT IT WORK!!!!1!1one!!1!"
OH FUCK WHY WONT IT WORK!!!!1!1one!!1!
$ cat /etc/openvpn/up.sh

sysctl -w net.ipv4.ip_forward=1
sysctl -w net.ipv6.conf.all.forwarding=1

ip link set $dev up promisc on mtu $tun_mtu

brctl addif br0 $dev

iptables -t nat -A POSTROUTING -s -o eth0 -j MASQUERADE

service radvd restart

$ sudo lsof -i ":openvpn"
radvd   2486  root    6u  IPv4  12816      0t0  TCP srwz.us:openvpn (LISTEN)
radvd   2487 radvd    6u  IPv4  12816      0t0  TCP srwz.us:openvpn (LISTEN)

WHAT??? radvd is listening on OpenVPN’s port?

Some background:  I was restarting radvd in the up script because it’s set to advertise on tap0, but tap0 doesn’t exist when the system boots, so instead of messing with the init scripts, I decided to just restart radvd in the up script. However, since the up script is executed as a subprocess of OpenVPN, it apparently inherits OpenVPN’s sockets, and radvd in turn inherits the shell script’s sockets, causing problems when you restart OpenVPN (even with SIGHUP, I would assume). *

Now I do have IgnoreIfMissing on; in my radvd.conf file (it’s not the default yet in the radvd 1.7 that ships with natty), but I didn’t realize that starting radvd succeeded when tap0 didn’t exist, which is why I was doing it in the up file.  radvd rereads its config file on SIGHUP, so to fix the issue, I simply changed this line in the up script:

service radvd restart


kill -HUP `cat /var/run/radvd/radvd.pid`

and restarting OpenVPN worked again.

Time to go to bed now.  I hope this helps someone.

* Disclaimer:  I don’t have 200 years of UNIX experience like some people do, so I may be a little bit wrong about this.  But I’m probably right.  :)