'Device or resource busy' error

[luckypoem]

root@RegalMusty-VM:/udptunnel-by-astroza# ls
LICENSE README.md include server.c tun.c
Makefile client.c scripts socket.c util.c
root@RegalMusty-VM:/udptunnel-by-astroza# make
gcc -Wall -I./include -c socket.c
gcc -Wall -I./include -c tun.c
gcc -Wall -I./include -c util.c
gcc -Wall -I./include -c client.c
gcc -Wall -I./include -c server.c
gcc socket.o tun.o util.o client.o -o client
gcc socket.o tun.o util.o server.o -o server
root@RegalMusty-VM:/udptunnel-by-astroza# ls
LICENSE client include server.c socket.o util.c
Makefile client.c scripts server.o tun.c util.o
README.md client.o server socket.c tun.o
root@RegalMusty-VM:/udptunnel-by-astroza# ./server 53 my-password
perror: Device or resource busy
root@RegalMusty-VM:~/udptunnel-by-astroza#

how to fix it?

[Filius-Patris]

There's already a process listening on port 53 probably. Use ss -l | grep 53 to see if this is the case.

[peacand]

Or you may have already a tun0 interface (it was my case). You can check with "ifconfig". If you see a tun0 interface, then you need to change every "tun0" into "tun1" or "tun2" in this repo (C code + shell scripts)