Manually verify outbound e-mail delivery from a machine with mail from the shell, either empty or with a typed message body.

Check a download or page response by its MIME type in Cucumber, using Webrat or Capybara; the Selenium webdriver does not support this approach.

Puppet catalog compilation can fail with ArgumentError: Invalid resource type when plugin sync or environments are misconfigured. Missing Ruby files in /var/lib/puppet/lib can trigger the error.

A reusable ~/.ssh/config template can simplify SSH access with host aliases and keepalive settings, then be adapted to personal needs.

VCR can stub remote API calls in tests while still letting you inspect what was sent, including request payloads, through WebMock.

A small helper adds a dismissible on-screen badge showing the current Rails environment to prevent confusion between development, test, and production.

MySQL can record every received query for debugging at the cost of performance. Enabling the general query log helps inspect database activity on non-production systems.

Create and list OpenStack Nova flavors by defining RAM, disk, swap, and vCPU resources for instances.

Dual-monitor setups with NVIDIA on Linux can crash X when DDC/CI is enabled on Dell displays; disabling DDC/CI avoids the failure.

Redirecting all requests from one host to another preserves path and query string while avoiding duplicate hosts and broken links.

Inspecting the generated Ruby for erb or haml templates helps debug rendering issues and understand what Rails executes. lookup_context.find_template and the template handler return the compiled output code.

Rails 3 auto-converts ActiveRecord times to UTC by default, which can break code using Time.now or Time.parse; local time and non-aware attributes restore the older behavior.

RubyGems 1.6.0 can break Rails 2.x with ActiveSupport::Dependencies::Mutex NameError during startup; loading thread before boot.rb prevents the failure.

Many MySQL or MariaDB connections can make SHOW PROCESSLIST hard to scan; sleeping sessions can be hidden with a pager filter or by querying metadata directly.

Common TLS failures can block secure connections and are often hard to diagnose. Typical symptoms point to certificate, protocol, or handshake issues and debugging clues help narrow them down.

git remote -v lists configured repository endpoints and shows which URLs are used for fetching and pushing.

bundle install can fail with Bundler::HTTPError while contacting the dependency API; upgrading Bundler to 1.2.4 or newer removes the misleading error.

Checking response status in Cucumber can verify error handling and redirects during acceptance tests. Webrat and Capybara expose status information for custom step definitions.

List PostgreSQL database sizes in megabytes with pg_database_size, useful for spotting large databases and planning storage.

Solr can start normally yet still return 404 Not Found when its log directory is not writable for the runtime user.

Accessing the Rails session ID is only possible when a session ID exists; exposing it is risky and should be done carefully.

Passenger can start a Rails app in the wrong environment unless Apache is configured with the correct RailsEnv or RackEnv setting.

RabbitMQ plugins on Ubuntu 12.04 require the full rabbitmq-plugins path because the binary is not in the default PATH.

Time zone mismatches can make Time.now differ from expected local time; upgrading Spreewald to 0.6.6 may correct the timezone switch bug.