While trying to install zsteg on Ubuntu Server (Linux 4.8.0-49-generic x86_64) I encounter the following error:

$ sudo gem install zsteg
Building native extensions.  This could take a while...
ERROR:  Error installing zsteg:
        ERROR: Failed to build gem native extension.

    current directory: /var/lib/gems/2.3.0/gems/rainbow-2.2.2/ext
/usr/bin/ruby2.3 mkrf_conf.rb

current directory: /var/lib/gems/2.3.0/gems/rainbow-2.2.2/ext
/usr/bin/ruby2.3 -rubygems /usr/share/rubygems-integration/all/gems/rake-10.5.0/bin/rake RUBYARCHDIR=/var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/rainbow-2.2.2 RUBYLIBDIR=/var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/rainbow-2.2.2
/usr/bin/ruby2.3: No such file or directory -- /usr/share/rubygems-integration/all/gems/rake-10.5.0/bin/rake (LoadError)

rake failed, exit code 1

Gem files will remain installed in /var/lib/gems/2.3.0/gems/rainbow-2.2.2 for inspection.
Results logged to /var/lib/gems/2.3.0/extensions/x86_64-linux/2.3.0/rainbow-2.2.2/gem_make.out

ruby2.3, ruby-dev and rake are installed

and also tried:

gem update --system

If I don't use sudo, I get: ERROR: While executing gem ... (Gem::FilePermissionError) You don't have write permissions for the /var/lib/gems/2.3.0 directory.

Please help.