I am in process of installing Redmine app via RedmineInstall documentation I try step 5 :
bundle exec rake db:migrate
bundler: command not found: rake
Install missing gem executables with ´bundle install´
Using rake 11.2.2
rake db:migrate in your redmine directory without
bundle exec and see if that resolves your issue.
Rails usually provides bin stubs for rake and other gem files, so that bundle exec is not necessary or will even fail because it will look in an other gem directory where, in this case, rake might not be installed.