kali Linux自带BEEF框架，长时间搁置后启动报错：
root@kali:/usr/share/beef-xss# ./beef
Traceback (most recent call last):
14: from ./beef:32:in `<main>'
13: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
12: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
11: from /usr/share/beef-xss/core/loader.rb:16:in `<top (required)>'
10: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
9: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
8: from /usr/lib/ruby/vendor_ruby/rubydns.rb:23:in `<top (required)>'
7: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
6: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
5: from /usr/lib/ruby/vendor_ruby/rubydns/message.rb:21:in `<top (required)>'
4: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
3: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
2: from /usr/lib/ruby/vendor_ruby/eventmachine.rb:8:in `<top (required)>'
1: from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
/usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require': cannot load such file -- rubyeventmachine (LoadError)
解决方法：
卸载beef，ruby
#apt remove ruby
#apt remove beef-xss
#apt-get install ruby
#apt-get install ruby-dev libpcap-dev
#gem install eventmachine
#apt-get install beef-xss
问题解决，重新启动BEEF无报错