My server is Debian 10, I install OpenProject using apt and at the end of the installation I got this:

[openproject] ./bin/postinstall

rake aborted!

PG::ConnectionBad: fe_sendauth: no password supplied

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/pg-1.1.4/lib/pg.rb:56:in `initialize'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/pg-1.1.4/lib/pg.rb:56:in `new'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/pg-1.1.4/lib/pg.rb:56:in `connect'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/postgresql_adapter.rb:46:in `postgresql_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:889:in `new_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:933:in `checkout_new_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:912:in `try_to_checkout_new_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:873:in `acquire_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:595:in `checkout'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:439:in `connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:1121:in `retrieve_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_handling.rb:238:in `retrieve_connection'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activerecord-6.0.1/lib/active_record/connection_handling.rb:206:in `connection'

/opt/openproject/lib/open_project/null_db_fallback.rb:35:in `fallback'

/opt/openproject/config/initializers/05-null_db_fallback.rb:36:in `<top (required)>'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:319:in `load'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:319:in `block in load'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:291:in `load_dependency'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:319:in `load'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/engine.rb:667:in `block in load_config_initializer'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/notifications.rb:182:in `instrument'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/engine.rb:666:in `load_config_initializer'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/engine.rb:624:in `block (2 levels) in <class:Engine>'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/engine.rb:623:in `each'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/engine.rb:623:in `block in <class:Engine>'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/initializable.rb:32:in `instance_exec'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/initializable.rb:32:in `run'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/initializable.rb:61:in `block in run_initializers'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/initializable.rb:50:in `each'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/initializable.rb:50:in `tsort_each_child'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/initializable.rb:60:in `run_initializers'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/application.rb:363:in `initialize!'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/railtie.rb:190:in `public_send'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/railtie.rb:190:in `method_missing'

/opt/openproject/config/environment.rb:34:in `<top (required)>'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:325:in `require'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:325:in `block in require'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:291:in `load_dependency'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/activesupport-6.0.1/lib/active_support/dependencies.rb:325:in `require'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/application.rb:339:in `require_environment!'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/railties-6.0.1/lib/rails/application.rb:515:in `block in run_tasks_blocks'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/rake-13.0.1/exe/rake:27:in `<top (required)>'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/cli/exec.rb:74:in `load'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/cli/exec.rb:74:in `kernel_load'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/cli/exec.rb:28:in `run'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/cli.rb:465:in `exec'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/cli.rb:27:in `dispatch'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/vendor/thor/lib/thor/base.rb:466:in `start'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/cli.rb:18:in `start'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/exe/bundle:30:in `block in <top (required)>'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/friendly_errors.rb:124:in `with_friendly_errors'

/opt/openproject/vendor/bundle/ruby/2.6.0/gems/bundler-2.0.2/exe/bundle:22:in `<top (required)>'

/opt/openproject/bin/bundle:3:in `load'

/opt/openproject/bin/bundle:3:in `<main>'

Tasks: TOP => db:migrate => db:load_config => environment

(See full trace by running task with --trace)