What is the easiest way to detect that a vpnc connection on Linux/Ubuntu has disconnected?
Manually, I think the way to detect is to check whether the interface (tun0) appears in /sbin/ifconfig output. Is there a better way to find out immediately, so that a script can be run to restart the connection?
The script /etc/vpnc/vpnc-script is called on various events, including connect and disconnect.
This sounds like you are using ubuntu or debian. If you are, the scripts
/etc/vpnc/vpnc-script-disconnect-action
and
/etc/vpnc/vpnc-script-post-disconnect-action
are called for the relevant events. You can create those files if they don't exist, and put whatever logic you want in there.
If you aren't using a debian-based distribution with these sub-scripts, you can modify /etc/vpnc/vpnc-script directly to add whatever logic you want.
If you are going to have logic to call vpnc-connect again, I recommend disconnecting that from the disconnect script somehow so you don't end up in an infinite loop.
I use a cron to take care of it so I can easily change it without having to remember what script I edited. The cron job is below.
*/15 * * * * [[ -d /sys/devices/virtual/net/tun0 ]] || /usr/sbin/vpnc /etc/vpnc/yourconf.conf
Typically the VPN connection should not break so frequently. In your case, you can first try to diagnose the real connectivity issue instead of writing scripts to automatically connect to the vpn when disconnected.
The below worked for me:
/sbin/ifconfig | /bin/grep -q tun0 || sudo /usr/sbin/vpnc-connect
