Linux – way to find out which program is segfault-ing

To find what arguments were passed to pdnsd, I'd do:

[~]> pgrep -l pdnsd
1373 pdnsd
[~]> cat /proc/1373/cmdline 
/usr/sbin/pdnsd--daemon-p/var/run/pdnsd.pid[~]> 

(cmdline file entries are separated by null characters; use something like tr '\0' '\n' </proc/<pid>/cmdline to see more legible output.)

/proc/<pid>/ contains a lot of information.

It doesn't looks like the kernel exposes this information. Therefore, short of kernel debugging, I don't think you can know this. The best you can do is list all processes that have tun or tap devices open like this:

lsof /dev/net/tun

So that will narrow it down, but in the case where there are multiple active tun interfaces on the system, it doesn't tell you which process is managing which tunnel.

When a process wants to create a tun interface, it opens /dev/net/tun no matter which tun interface it intends to use. Then, it either lets the kernel dynamically assign a new tun interface name (like tun0, tun1, tun2 etc...) or it sets a chosen name. This is done with an ioctl call with code TUNSETIFF. So unless you get to trace that ioctl call, there isn't really a way to tell what name got assigned.