Failed to build gem native extension for ruby-debug-base19x - ruby-on-rails

Question

I am new to Ruby On Rails, I am installing the gem, ruby-debug-base19x. But without successful. I found some similar answer but no help.
Building native extensions. This could take a while...
ERROR: Error installing ruby-debug-base19x:
ERROR: Failed to build gem native extension.
/opt/redmine-2.4.2-0/ruby/bin/ruby extconf.rb
checking for vm_core.h... no
/opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib /ruby_core_source.rb:39: Use RbConfig instead of obsolete and deprecated Config.
checking for vm_core.h... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/opt/redmine-2.4.2-0/ruby/bin/ruby
--with-ruby-dir
--without-ruby-dir
--with-ruby-include
--without-ruby-include=${ruby-dir}/include
--with-ruby-lib
--without-ruby-lib=${ruby-dir}/lib
/opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/contrib/uri_ext.rb:270:in `block (2 levels) in read': Failed to download http://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.3-p484.tar.gz: Forbidden (RuntimeError)
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1323:in `block (2 levels) in transport_request'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:2672:in `reading_body'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1322:in `block in transport_request'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1317:in `catch'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1317:in `transport_request'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1294:in `request'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1287:in `block in request'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:746:in `start'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/net/http.rb:1285:in `request'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/contrib/uri_ext.rb:239:in `block in read'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/contrib/uri_ext.rb:286:in `connect'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/contrib/uri_ext.rb:234:in `read'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/contrib/uri_ext.rb:128:in `download'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/ruby_core_source.rb:55:in `block in create_makefile_with_core'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/1.9.1/tempfile.rb:320:in `open'
from /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/ruby_core_source-0.1.5/lib/ruby_core_source.rb:51:in `create_makefile_with_core'
from extconf.rb:19:in `<main>'
Requesting http://ftp.ruby-lang.org/pub/ruby/1.9/ruby-1.9.3-p484.tar.gz
Gem files will remain installed in /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/linecache19-0.5.12 for inspection.
Results logged to /opt/redmine-2.4.2-0/ruby/lib/ruby/gems/1.9.1/gems/linecache19-0.5.12/ext/trace_nums/gem_make.out
I also check the mkmf.log,
have_header: checking for vm_core.h... -------------------- no
"gcc -E -I/opt/redmine-2.4.2-0/ruby/include/ruby-1.9.1/x86_64-linux -I/opt/redmine-2.4.2-0/ruby/include/ruby-1.9.1/ruby/backward -I/opt/redmine-2.4.2-0/ruby/include/ruby-1.9.1 -I. -I/opt/redmine-2.4.2-0/ruby/include/ruby-1.9.1/ruby-1.9.3-p484 -I/opt/redmine-2.4.2-0/common/include -fPIC -I/bitnami/rubystack-linux-x64/output/ImageMagick/include/ImageMagick -I/bitnami/rubystack-linux-x64/output/ImageMagick/include/ImageMagick -O3 conftest.c -o conftest.i"
conftest.c:3:21: error: vm_core.h: No such file or directory
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: #include <vm_core.h>
/* end */

Answer 1

You got a 403 trying to download the source tarball. From the log:
Failed to download http://ftp.ruby-lang.org/[-snipped-].tar.gz: Forbidden
I just tried the URL and it's accessible for me. Try again. Maybe it was a one-time hiccup.