Dealing with "server has not started in 15 seconds"

Basic debugging step

First of all, you need to run:

eye l config.rb -f

to start eye in the foreground and see why it's not working.

List of possible errors

Sigar.so: undefined symbol: sigar_skip_token`

One of the most popular errors is:

ruby: symbol lookup error: /usr/local/rvm/gems/ruby-2.4.1/gems/sigar-0.7.3/lib/sigar.so: undefined symbol: sigar_skip_token

(Actually, it happened on all of my Ubuntu/Debian servers).

The fix is quite simple:

gem install sigar -- --with-cppflags="-fgnu89-inline"

or for bundler:

bundle config --local build.sigar '--with-cppflags="-fgnu89-inline"'