diff --git a/elasticgraph-local/lib/elastic_graph/local/docker_runner.rb b/elasticgraph-local/lib/elastic_graph/local/docker_runner.rb
index 8367c9158..fc49ae5b3 100644
--- a/elasticgraph-local/lib/elastic_graph/local/docker_runner.rb
+++ b/elasticgraph-local/lib/elastic_graph/local/docker_runner.rb
@@ -23,15 +23,15 @@ def initialize(variant, port:, ui_port:, version:, env:, ready_log_line:, daemon
         @output = output
       end
 
+      # :nocov: -- difficult to test `exec` behavior (replaces current process)
       def boot
-        # :nocov: -- this is actually covered via a call from `boot_as_daemon` but it happens in a forked process so simplecov doesn't see it.
         halt
 
         prepare_docker_compose_run "up" do |command|
           exec(command) # we use `exec` so that our process is replaced with that one.
         end
-        # :nocov:
       end
+      # :nocov:
 
       def halt
         prepare_docker_compose_run "down --volumes" do |command|
@@ -40,26 +40,11 @@ def halt
       end
 
       def boot_as_daemon(halt_command:)
-        with_pipe do |read_io, write_io|
-          fork do
-            # :nocov: -- simplecov can't track coverage that happens in another process
-            read_io.close
-            Process.daemon
-            pid = Process.pid
-            $stdout.reopen(write_io)
-            $stderr.reopen(write_io)
-            puts pid
-            boot
-            write_io.close
-            # :nocov:
-          end
-
-          # The `Process.daemon` call in the subprocess changes the pid so we have to capture it this way instead of using
-          # the return value of `fork`.
-          pid = read_io.gets.to_i
+        halt
 
-          @output.puts "Booting #{@variant}; monitoring logs for readiness..."
+        @output.puts "Booting #{@variant}; monitoring logs for readiness..."
 
+        pid = spawn_docker_compose_up do |read_io|
           ::Timeout.timeout(
             @daemon_timeout,
             ::Timeout::Error,
@@ -76,20 +61,46 @@ def boot_as_daemon(halt_command:)
               break if @ready_log_line.match?(line.to_s)
             end
           end
+        end
 
-          @output.puts
-          @output.puts
-          @output.puts <<~EOS
-            Success! #{@variant} #{@version} (pid: #{pid}) has been booted for the #{@env} environment on port #{@port}.
-            It will continue to run in the background as a daemon. To halt it, run:
+        # Detach so the process continues running after this Ruby process exits.
+        ::Process.detach(pid)
 
-            #{halt_command}
-          EOS
-        end
+        @output.puts
+        @output.puts
+        @output.puts <<~EOS
+          Success! #{@variant} #{@version} (pid: #{pid}) has been booted for the #{@env} environment on port #{@port}.
+          It will continue to run in the background as a daemon. To halt it, run:
+
+          #{halt_command}
+        EOS
       end
 
       private
 
+      def spawn_docker_compose_up
+        read_io, write_io = ::IO.pipe
+
+        pid = prepare_docker_compose_run("up") do |command|
+          spawn(
+            command,
+            chdir: ::Dir.pwd,
+            out: write_io,
+            err: write_io
+          )
+        end
+
+        write_io.close # We don't write from the parent process
+
+        begin
+          yield read_io
+        ensure
+          read_io.close
+        end
+
+        pid
+      end
+
       def prepare_docker_compose_run(*commands)
         name = "#{@env}-#{@version.tr(".", "_")}"
 
@@ -101,17 +112,6 @@ def prepare_docker_compose_run(*commands)
           yield full_command
         end
       end
-
-      def with_pipe
-        read_io, write_io = ::IO.pipe
-
-        begin
-          yield read_io, write_io
-        ensure
-          read_io.close
-          write_io.close
-        end
-      end
     end
   end
 end
diff --git a/elasticgraph-local/lib/elastic_graph/local/rake_tasks.rb b/elasticgraph-local/lib/elastic_graph/local/rake_tasks.rb
index 686f02354..8dc00926c 100644
--- a/elasticgraph-local/lib/elastic_graph/local/rake_tasks.rb
+++ b/elasticgraph-local/lib/elastic_graph/local/rake_tasks.rb
@@ -475,9 +475,10 @@ def define_other_tasks
 
           # :nocov: -- we can't test `open` behavior through a test
           unless args.fetch(:no_open)
-            fork do
+            Thread.new do
               sleep 3 # give the app a bit of time to boot before we try to open it.
-              sh "open http://localhost:#{port}/"
+              url = "http://localhost:#{port}/"
+              system("open", url) || system("xdg-open", url)
             end
           end
           # :nocov:
diff --git a/elasticgraph-local/sig/elastic_graph/local/docker_runner.rbs b/elasticgraph-local/sig/elastic_graph/local/docker_runner.rbs
index ce9c997e5..6b258b9e8 100644
--- a/elasticgraph-local/sig/elastic_graph/local/docker_runner.rbs
+++ b/elasticgraph-local/sig/elastic_graph/local/docker_runner.rbs
@@ -27,8 +27,8 @@ module ElasticGraph
 
       private
 
-      def prepare_docker_compose_run: (*::String) { (::String) -> void } -> void
-      def with_pipe: [T] () { (::IO, ::IO) -> T } -> T
+      def spawn_docker_compose_up: () { (::IO) -> void } -> ::Integer
+      def prepare_docker_compose_run: [T] (*::String) { (::String) -> T } -> T
     end
   end
 end
diff --git a/spec_support/lib/elastic_graph/spec_support/in_sub_process.rb b/spec_support/lib/elastic_graph/spec_support/in_sub_process.rb
index 6af5af01e..a7cbbd659 100644
--- a/spec_support/lib/elastic_graph/spec_support/in_sub_process.rb
+++ b/spec_support/lib/elastic_graph/spec_support/in_sub_process.rb
@@ -14,7 +14,13 @@ module ElasticGraph
     # Runs the provided block in a subprocess. Any failures in the sub process get
     # caught and re-raised in the parent process. Also, this returns the return value
     # of the child process (using `Marshal` to send it across a pipe).
+    #
+    # On JRuby, fork is unavailable, so this skips the test instead.
     def in_sub_process(&block)
+      # :nocov: -- we only cover one side of this conditional for a given run of the test suite
+      skip "Test requires fork (unavailable on JRuby)" if RUBY_ENGINE == "jruby"
+      # :nocov:
+
       SubProcess.new.run(&block)
     end
   end