When I was trying to run the rails application following segmentation error has occurred:

=> Booting Thin
=> Rails 4.2.6 application starting in development on http://localhost:4000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Thin web server (v1.7.0 codename Dunder Mifflin)
Maximum connections set to 1024
Listening on localhost:4000, CTRL+C to stop
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/eventmachine-1.2.0.1/lib/eventmachine.rb:202: [BUG] Segmentation fault at 0x000000
ruby 2.2.5p319 (2016-04-26 revision 54774) [i686-linux]

-- Control frame information -----------------------------------------------
c:0016 p:---- s:0065 e:000064 CFUNC  :release_machine
c:0015 p:0032 s:0062 e:000061 RESCUE /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/eventmachine-1.2.0.1/lib/eventmachine.rb:202
c:0014 p:0360 s:0059 E:002114 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/eventmachine-1.2.0.1/lib/eventmachine.rb:205
c:0013 p:0057 s:0052 E:001da8 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/backends/base.rb:73
c:0012 p:0111 s:0048 E:001a64 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/server.rb:162
c:0011 p:0176 s:0045 e:000044 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/rack-1.6.4/lib/rack/handler/thin.rb:19
c:0010 p:0196 s:0034 E:001de0 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/rack-1.6.4/lib/rack/server.rb:286
c:0009 p:0043 s:0028 E:0006ec METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/server.rb:80
c:0008 p:0044 s:0025 E:001c88 BLOCK  /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:80 [FINISH]
c:0007 p:---- s:0022 e:000021 CFUNC  :tap
c:0006 p:0031 s:0019 E:001c54 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75
c:0005 p:0033 s:0016 E:001cc0 METHOD /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:39
c:0004 p:0116 s:0012 E:001cfc TOP    /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands.rb:17 [FINISH]
c:0003 p:---- s:0008 e:000007 CFUNC  :require
c:0002 p:0034 s:0004 E:0005ec EVAL   bin/rails:4 [FINISH]
c:0001 p:0000 s:0002 E:000844 TOP    [FINISH]

 -- Ruby level backtrace information ----------------------------------------
bin/rails:4:in `<main>'
bin/rails:4:in `require'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands.rb:17:in `<top (required)>'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75:in `server'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75:in `tap'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:80:in `block in server'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/railties-4.2.6/lib/rails/commands/server.rb:80:in `start'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/rack-1.6.4/lib/rack/server.rb:286:in `start'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/rack-1.6.4/lib/rack/handler/thin.rb:19:in `run'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/server.rb:162:in `start'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/backends/base.rb:73:in `start'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/eventmachine-1.2.0.1/lib/eventmachine.rb:205:in `run'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/eventmachine-1.2.0.1/lib/eventmachine.rb:202:in `ensure in run'
/home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/eventmachine-1.2.0.1/lib/eventmachine.rb:202:in `release_machine'

     -- Machine register context ------------------------------------------------
  GS: 0x00000033  FS: 0x00000000  ES: 0x0000007b  DS: 0x0000007b EDI: 0xb6e56104
 ESI: 0x0995ac08 EBP: 0xbfa1b9a8 ESP: 0xbfa1b96c EBX: 0xb52b9000 EDX: 0x00000000
 ECX: 0x00000020 EAX: 0x0d0e58d0 TRA: 0x0000000e ERR: 0x00000014 EIP: 0x00000000
  CS: 0x00000073 EFL: 0x00010296 UES: 0xbfa1b96c  SS: 0x0000007b

     -- C level backtrace information -------------------------------------------
/home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/libruby.so.2.2(rb_vm_bugreport+0x4ac) [0xb7590adc] vm_dump.c:693
/home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/libruby.so.2.2(rb_bug_context+0x54) [0xb7431054] error.c:425
/home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/libruby.so.2.2(sigsegv+0x43) [0xb7507283] signal.c:879
 [0xb76e0c64]

  -- Other runtime information -----------------------------------------------
* Loaded script: bin/rails
* Loaded features:
    0 enumerator.so
    1 rational.so
    2 complex.so
    3 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/2.2.0/i686-linux/enc/encdb.so
    4 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/2.2.0/i686-linux/enc/trans/transdb.so
    5 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/2.2.0/unicode_normalize.rb
    6 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/2.2.0/i686-linux/rbconfig.rb
    7 thread.rb
    8 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/2.2.0/i686-linux/thread.so
    9 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/compatibility.rb
   10 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/defaults.rb
   11 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/deprecate.rb
   12 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/errors.rb
   13 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/version.rb
   14 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/requirement.rb
   15 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/platform.rb
   16 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/basic_specification.rb
   17 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/stub_specification.rb
   18 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/util/stringio.rb
   19 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/specification.rb
   20 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/exceptions.rb
   21 /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_gem.rb
  795 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/loofah-2.0.3/lib/loofah/elements.rb
  796 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/loofah-2.0.3/lib/loofah/html5/whitelist.rb
  797 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/loofah-2.0.3/lib/loofah/html5/scrub.rb
  952 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/sass-3.4.22/lib/sass/shared.rb
  953 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/sass-3.4.22/lib/sass/media.rb
 1388 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/bundler/gems/paperclip-d61b7069c2ce/lib/paperclip/validators/attachment_size_validator.rb
 1389 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/bundler/gems/paperclip-d61b7069c2ce/lib/paperclip/validators/media_type_spoof_detection_validator.rb
 2344 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/server.rb
 2345 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/backends/base.rb
 2346 /home/ubuntu/.rvm/gems/ruby-2.2.5@easy_math/gems/thin-1.7.0/lib/thin/backends/tcp_server.rb

Process memory map:

b76d1000-b76d5000 r--p 0030c000 08:02 3140460    /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/libruby.so.2.2.0
b76d5000-b76d7000 rw-p 00310000 08:02 3140460    /home/ubuntu/.rvm/rubies/ruby-2.2.5/lib/libruby.so.2.2.0
b76d7000-b76e0000 rw-p 00000000 00:00 0 
b76e0000-b76e1000 r-xp 00000000 00:00 0          [vdso]
b76e1000-b76e3000 r--p 00000000 00:00 0          [vvar]
b76e3000-b7703000 r-xp 00000000 08:02 5596214    /lib/i386-linux-gnu/ld-2.19.so
b7703000-b7704000 r--p 0001f000 08:02 5596214    /lib/i386-linux-gnu/ld-2.19.so
b7704000-b7705000 rw-p 00020000 08:02 5596214    /lib/i386-linux-gnu/ld-2.19.so
bf21f000-bfa1e000 rw-p 00000000 00:00 0 
[NOTE]
You may have encountered a bug in the Ruby interpreter or extension libraries.
Bug reports are welcome.
For details: http://www.ruby-lang.org/bugreport.html
Aborted (core dumped)

Looks like a new issue: https://github.com/eventmachine/eventmachine/issues/670

Try downgrading your eventmachine gem version:

gem uninstall eventmachine
gem install eventmachine -v 0.12.2