I installed Openproject on a Debain 8 system (package installation).

But when I start to run it, I get this error message:

$ sudo openproject run web
I, [2017-05-09T11:53:17.165010 #26466] INFO — : Refreshing Gem list
/opt/openproject/app/seeders/random_data/work_package_seeder.rb:84: warning: key :user is duplicated and overwritten on line 87
E, [2017-05-09T11:53:34.005991 #26466] ERROR — : adding listener failed addr=127.0.0.1:6000 (in use)
E, [2017-05-09T11:53:34.006436 #26466] ERROR — : retrying in 0.5 seconds (4 tries left)
E, [2017-05-09T11:53:34.508081 #26466] ERROR — : adding listener failed addr=127.0.0.1:6000 (in use)
E, [2017-05-09T11:53:34.508360 #26466] ERROR — : retrying in 0.5 seconds (3 tries left)
E, [2017-05-09T11:53:35.008931 #26466] ERROR — : adding listener failed addr=127.0.0.1:6000 (in use)
E, [2017-05-09T11:53:35.009099 #26466] ERROR — : retrying in 0.5 seconds (2 tries left)
E, [2017-05-09T11:53:35.511460 #26466] ERROR — : adding listener failed addr=127.0.0.1:6000 (in use)
E, [2017-05-09T11:53:35.511801 #26466] ERROR — : retrying in 0.5 seconds (1 tries left)
E, [2017-05-09T11:53:36.014392 #26466] ERROR — : adding listener failed addr=127.0.0.1:6000 (in use)
E, [2017-05-09T11:53:36.014855 #26466] ERROR — : retrying in 0.5 seconds (0 tries left)
E, [2017-05-09T11:53:36.517497 #26466] ERROR — : adding listener failed addr=127.0.0.1:6000 (in use)
bundler: failed to load command: unicorn (/opt/openproject/vendor/bundle/ruby/2.3.0/bin/unicorn)
Errno::EADDRINUSE: Address already in use - bind(2) for 127.0.0.1:6000
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/socket_helper.rb:149:in `bind’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/socket_helper.rb:149:in `new_tcp_server’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/socket_helper.rb:129:in `bind_listen’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:231:in `listen’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:808:in `block in bind_new_listeners!’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:808:in `each’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:808:in `bind_new_listeners!’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/lib/unicorn/http_server.rb:130:in `start’
/opt/openproject/vendor/bundle/ruby/2.3.0/gems/unicorn-5.1.0/bin/unicorn:126:in `<top (required)>’
/opt/openproject/vendor/bundle/ruby/2.3.0/bin/unicorn:23:in `load’
/opt/openproject/vendor/bundle/ruby/2.3.0/bin/unicorn:23:in `<top (required)>’

Any idea why this happens and how to fix it? Thanks.