mysql2 gem not loaded installing redmine-agile - ruby-on-rails

Question

I'm trying to install the Redmine Agile plugin, and I can't get through step 4:
/var/www/html/redmine$ sudo bundle exec rake redmine:plugins NAME=redmine_agile RAILS_ENV=production
(in /usr/share/redmine)
rake aborted!
Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/usr/share/redmine/lib/tasks/redmine.rake:52:in `block (2 levels) in <top (required)>'
/var/lib/gems/2.3.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
Caused by:
Gem::LoadError: mysql2 is not part of the bundle. Add it to your Gemfile.
/var/lib/gems/2.3.0/gems/bundler-1.16.2/lib/bundler/rubygems_integration.rb:408:in `block (2 levels) in replace_gem'
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/usr/share/redmine/lib/tasks/redmine.rake:52:in `block (2 levels) in <top (required)>'
/var/lib/gems/2.3.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
Tasks: TOP => redmine:plugins:migrate => environment
(See full trace by running task with --trace)
I previously had been unable to sudo gem install mysql2, but got around that by following this answer.
I did try adding gem "mysql2", but that did not resolve the issue.
/var/www/html/redmine$ cat plugins/redmine_agile/Gemfile
gem "redmine_crm"
gem "mysql2"
I'm not sure what to make of and ensure its version is at the minimum required by ActiveRecord. I'm not sure how to check what that is. I know I can set versions of a gem in the Gemfile, but I don't know what it would be set to.
I'm on Ubuntu 16.04.4 LTS, MySQL 5.7.22. I'm serving Redmine using something similar to this answer.
UPDATE
When I tried to rake as www-data, the error I got changed to
www-data#host:/usr/share/redmine/public/plugins/redmine_agile$ bundle exec rake redmine:plugins NAME=redmine_agile RAILS_ENV=production
`/home/ubuntu` is not writable.
Bundler will use `/tmp/bundler/home/ubuntu' as your home directory temporarily.
Could not find gem 'redmine_crm' in any of the gem sources listed in your Gemfile.
Run `bundle install` to install missing gems.
(Trying to rake from /var/www/html/redmine kept getting me the mysql2 error.)
I then tried to install redmine_crm. I couldn't do this as www-data, so I did it as root:
/var/www/html/redmine/plugins/redmine_agile$ sudo gem install redmine_crm
I then tried bundle install but got
There was an error while trying to write to
`/usr/share/redmine/public/plugins/redmine_agile/Gemfile.lock`. It is likely that you need to grant
write permissions for that path.
So I ran that as root.
/var/www/html/redmine/plugins/redmine_agile$ sudo bundle install
Don't run Bundler as root. Bundler can ask for sudo if it is needed, and installing your bundle as
root will break this application for all non-root users on this machine.
Resolving dependencies...
Using rake 12.3.2
Using i18n 0.7.0
Using json 1.8.3
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 4.2.6
Using builder 3.2.3
Using erubis 2.7.0
Using nokogiri 1.6.7.2
Using rails-deprecated_sanitizer 1.0.3
Using rails-dom-testing 1.0.6
Using crass 1.0.4
Using loofah 2.2.2
Using rails-html-sanitizer 1.0.4
Using actionview 4.2.6
Using rack 1.6.4
Using rack-test 0.6.3
Using actionpack 4.2.6
Using globalid 0.4.1
Using activejob 4.2.6
Using mini_mime 1.0.0
Using mail 2.7.0
Using actionmailer 4.2.6
Using activemodel 4.2.6
Using arel 6.0.3
Using activerecord 4.2.6
Using bundler 1.16.2
Using concurrent-ruby 1.0.5
Using liquid 2.6.3
Using mysql2 0.5.2
Using thor 0.20.0
Using railties 4.2.6
Using sprockets 3.7.2
Using sprockets-rails 3.2.1
Using rails 4.2.6
Using redmine_crm 0.0.42
Bundle complete! 2 Gemfile dependencies, 37 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
Trying rake then got me a different error.
ubuntu#host:/var/www/html/redmine/plugins/redmine_agile$ sudo bundle exec rake redmine:plugins NAME=redmine_agile RAILS_ENV=production
(in /usr/share/redmine)
rake aborted!
NameError: uninitialized constant ActionDispatch::XmlParamsParser
/usr/share/redmine/config/application.rb:55:in `<class:Application>'
/usr/share/redmine/config/application.rb:8:in `<module:RedmineApp>'
/usr/share/redmine/config/application.rb:7:in `<top (required)>'
/usr/share/redmine/Rakefile:4:in `require'
/usr/share/redmine/Rakefile:4:in `<top (required)>'
/var/lib/gems/2.3.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
(See full trace by running task with --trace)
Trying that from the redmine per this answer directory failed with the mysql2 gem error.
ubuntu#host:/var/www/html/redmine/plugins/redmine_agile$ cd ../..
ubuntu#host:/var/www/html/redmine$ sudo bundle exec rake redmine:plugins NAME=redmine_agile RAILS_ENV=production
(in /usr/share/redmine)
rake aborted!
Gem::LoadError: Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/usr/share/redmine/lib/tasks/redmine.rake:52:in `block (2 levels) in <top (required)>'
/var/lib/gems/2.3.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
Caused by:
Gem::LoadError: mysql2 is not part of the bundle. Add it to your Gemfile.
/var/lib/gems/2.3.0/gems/bundler-1.16.2/lib/bundler/rubygems_integration.rb:408:in `block (2 levels) in replace_gem'
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/usr/share/redmine/lib/tasks/redmine.rake:52:in `block (2 levels) in <top (required)>'
/var/lib/gems/2.3.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
Tasks: TOP => redmine:plugins:migrate => environment
(See full trace by running task with --trace)

Answer 1

Unnecessary use of sudo to run a command as root is a common cause of issues to find resolve some gems.
In almost all cases, you should thus not not use sudo to run your rake tasks. Instead, use the user which normally usually runs the app server, e.g. www-data.
# first change to the user that usually runs your app
sudo -u www-data /bin/bash -i
/var/www/html/redmine
# Now run your rake task (without prefixing it with sudo)
bundle exec rake redmine:plugins NAME=redmine_agile RAILS_ENV=production

Answer 2

This error is clearly saying that you have not installed Gem 'mysql2' have you ran command bundle install? can you try following
On your project root folder please run following command
gem list mysql2
It should show you local gems and also list mysql2 as installed
In case it is not installed, that means you either you can't install mysql2 or you have not run bundle install command. Maybe you can try the following
Add the following line in your Gemfile
gem "mysql2", "0.3.14"
now run following command
bundle install
Now check if mysql2 is really installed
gem list mysql2
If yes then all good, hope it works.