How to debug “Vagrant cannot forward the specified ports on this VM” message

Question

I\'m trying to start a Vagrant instance and getting the following message:

Vagrant cannot forward the specified ports on this VM, since they
would collide wi         


        

Answer 1

I ran into this problem and it turned out RubyMine was still holding on to a port. I found out which application was holding on to the port (31337 in my case) by running this command:

lsof -i | grep LISTEN 

Output

node       1396 richard.nienaber    7u  IPv4 0xffffff802808b320      0t0  TCP *:20559 (LISTEN)
Dropbox    1404 richard.nienaber   19u  IPv4 0xffffff8029736c20      0t0  TCP *:17500 (LISTEN)
Dropbox    1404 richard.nienaber   25u  IPv4 0xffffff8027870160      0t0  TCP localhost:26165 (LISTEN)
rubymine  11668 richard.nienaber   39u  IPv6 0xffffff8024d8e700      0t0  TCP *:26162 (LISTEN)
rubymine  11668 richard.nienaber   65u  IPv6 0xffffff8020c6e440      0t0  TCP *:31337 (LISTEN)
rubymine  11668 richard.nienaber  109u  IPv6 0xffffff8024d8df80      0t0  TCP localhost:6942 (LISTEN)
rubymine  11668 richard.nienaber  216u  IPv6 0xffffff8020c6ef80      0t0  TCP localhost:63342 (LISTEN)