diff --git a/config/config.go b/config/config.go
index 5ffc0f8..d0879d1 100644
--- a/config/config.go
+++ b/config/config.go
@@ -18,12 +18,13 @@ import (
 var (
 	Config = &configuration{
 		Server: server{
-			Address:  "127.0.0.1",
-			Port:     7200,
-			Token:    "",
-			TLS:      false,
-			CertFile: "",
-			KeyFile:  "",
+			Address:           "127.0.0.1",
+			Port:              7200,
+			Token:             "",
+			TLS:               false,
+			CertFile:          "",
+			KeyFile:           "",
+			InteractiveStderr: true,
 		},
 		Nomad: nomad{
 			Address:   "127.0.0.1",
@@ -48,12 +49,13 @@ var (
 
 // server configures the Poseidon webserver.
 type server struct {
-	Address  string
-	Port     int
-	Token    string
-	TLS      bool
-	CertFile string
-	KeyFile  string
+	Address           string
+	Port              int
+	Token             string
+	TLS               bool
+	CertFile          string
+	KeyFile           string
+	InteractiveStderr bool
 }
 
 // nomad configures the used Nomad cluster.
diff --git a/configuration.example.yaml b/configuration.example.yaml
index 538ffeb..caca1b1 100644
--- a/configuration.example.yaml
+++ b/configuration.example.yaml
@@ -12,6 +12,8 @@ server:
   certfile: ./poseidon.crt
   # The path to the key file used for TLS
   keyfile: ./poseidon.key
+  # If true, an additional WebSocket connection will be opened to split stdout and stderr when executing interactively
+  interactiveStderr: true
 
 # Configuration of the used Nomad cluster
 nomad:
diff --git a/environment/default-job.hcl b/environment/default-job.hcl
index 1cd6390..0dd6c2d 100644
--- a/environment/default-job.hcl
+++ b/environment/default-job.hcl
@@ -1,10 +1,10 @@
 // This is the default job configuration that is used when no path to another default configuration is given
 
-job "default-poseidon-job" {
+job "python" {
   datacenters = ["dc1"]
   type = "batch"
 
-  group "default-poseidon-group" {
+  group "default-group" {
     ephemeral_disk {
       migrate = false
       size    = 10
@@ -23,13 +23,13 @@ job "default-poseidon-job" {
       weight = 100
     }
 
-    task "default-poseidon-task" {
+    task "default-task" {
       driver = "docker"
       kill_timeout = "0s"
       kill_signal = "SIGKILL"
 
       config {
-        image = "python:latest"
+        image = "drp.codemoon.xopic.de/openhpi/co_execenv_python:3.8"
         command = "sleep"
         args = ["infinity"]
         network_mode = "none"
diff --git a/nomad/api_querier.go b/nomad/api_querier.go
index 159695d..c579e46 100644
--- a/nomad/api_querier.go
+++ b/nomad/api_querier.go
@@ -24,8 +24,8 @@ type apiQuerier interface {
 	// DeleteRunner deletes the runner with the given Id.
 	DeleteRunner(runnerId string) (err error)
 
-	// ExecuteCommand runs a command in the passed allocation.
-	ExecuteCommand(allocationID string, ctx context.Context, command []string, tty bool,
+	// Execute runs a command in the passed allocation.
+	Execute(allocationID string, ctx context.Context, command []string, tty bool,
 		stdin io.Reader, stdout, stderr io.Writer) (int, error)
 
 	// loadRunners loads all allocations of the specified job.
@@ -72,7 +72,7 @@ func (nc *nomadAPIClient) DeleteRunner(runnerID string) (err error) {
 	return err
 }
 
-func (nc *nomadAPIClient) ExecuteCommand(allocationID string,
+func (nc *nomadAPIClient) Execute(allocationID string,
 	ctx context.Context, command []string, tty bool,
 	stdin io.Reader, stdout, stderr io.Writer) (int, error) {
 	allocation, _, err := nc.client.Allocations().Info(allocationID, nil)
diff --git a/nomad/api_querier_mock.go b/nomad/api_querier_mock.go
index 36b9075..9dcbe34 100644
--- a/nomad/api_querier_mock.go
+++ b/nomad/api_querier_mock.go
@@ -79,8 +79,8 @@ func (_m *apiQuerierMock) EvaluationStream(evalID string, ctx context.Context) (
 	return r0, r1
 }
 
-// ExecuteCommand provides a mock function with given fields: allocationID, ctx, command, tty, stdin, stdout, stderr
-func (_m *apiQuerierMock) ExecuteCommand(allocationID string, ctx context.Context, command []string, tty bool, stdin io.Reader, stdout io.Writer, stderr io.Writer) (int, error) {
+// Execute provides a mock function with given fields: allocationID, ctx, command, tty, stdin, stdout, stderr
+func (_m *apiQuerierMock) Execute(allocationID string, ctx context.Context, command []string, tty bool, stdin io.Reader, stdout io.Writer, stderr io.Writer) (int, error) {
 	ret := _m.Called(allocationID, ctx, command, tty, stdin, stdout, stderr)
 
 	var r0 int
diff --git a/nomad/executor_api_mock.go b/nomad/executor_api_mock.go
index 536f6a4..9adf9f8 100644
--- a/nomad/executor_api_mock.go
+++ b/nomad/executor_api_mock.go
@@ -14,13 +14,13 @@ import (
 	url "net/url"
 )
 
-// ExecutorApiMock is an autogenerated mock type for the ExecutorAPI type
-type ExecutorApiMock struct {
+// ExecutorAPIMock is an autogenerated mock type for the ExecutorAPI type
+type ExecutorAPIMock struct {
 	mock.Mock
 }
 
 // AllocationStream provides a mock function with given fields: ctx
-func (_m *ExecutorApiMock) AllocationStream(ctx context.Context) (<-chan *api.Events, error) {
+func (_m *ExecutorAPIMock) AllocationStream(ctx context.Context) (<-chan *api.Events, error) {
 	ret := _m.Called(ctx)
 
 	var r0 <-chan *api.Events
@@ -43,7 +43,7 @@ func (_m *ExecutorApiMock) AllocationStream(ctx context.Context) (<-chan *api.Ev
 }
 
 // DeleteRunner provides a mock function with given fields: runnerId
-func (_m *ExecutorApiMock) DeleteRunner(runnerId string) error {
+func (_m *ExecutorAPIMock) DeleteRunner(runnerId string) error {
 	ret := _m.Called(runnerId)
 
 	var r0 error
@@ -57,7 +57,7 @@ func (_m *ExecutorApiMock) DeleteRunner(runnerId string) error {
 }
 
 // EvaluationStream provides a mock function with given fields: evalID, ctx
-func (_m *ExecutorApiMock) EvaluationStream(evalID string, ctx context.Context) (<-chan *api.Events, error) {
+func (_m *ExecutorAPIMock) EvaluationStream(evalID string, ctx context.Context) (<-chan *api.Events, error) {
 	ret := _m.Called(evalID, ctx)
 
 	var r0 <-chan *api.Events
@@ -79,8 +79,29 @@ func (_m *ExecutorApiMock) EvaluationStream(evalID string, ctx context.Context)
 	return r0, r1
 }
 
+// Execute provides a mock function with given fields: allocationID, ctx, command, tty, stdin, stdout, stderr
+func (_m *ExecutorAPIMock) Execute(allocationID string, ctx context.Context, command []string, tty bool, stdin io.Reader, stdout io.Writer, stderr io.Writer) (int, error) {
+	ret := _m.Called(allocationID, ctx, command, tty, stdin, stdout, stderr)
+
+	var r0 int
+	if rf, ok := ret.Get(0).(func(string, context.Context, []string, bool, io.Reader, io.Writer, io.Writer) int); ok {
+		r0 = rf(allocationID, ctx, command, tty, stdin, stdout, stderr)
+	} else {
+		r0 = ret.Get(0).(int)
+	}
+
+	var r1 error
+	if rf, ok := ret.Get(1).(func(string, context.Context, []string, bool, io.Reader, io.Writer, io.Writer) error); ok {
+		r1 = rf(allocationID, ctx, command, tty, stdin, stdout, stderr)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
 // ExecuteCommand provides a mock function with given fields: allocationID, ctx, command, tty, stdin, stdout, stderr
-func (_m *ExecutorApiMock) ExecuteCommand(allocationID string, ctx context.Context, command []string, tty bool, stdin io.Reader, stdout io.Writer, stderr io.Writer) (int, error) {
+func (_m *ExecutorAPIMock) ExecuteCommand(allocationID string, ctx context.Context, command []string, tty bool, stdin io.Reader, stdout io.Writer, stderr io.Writer) (int, error) {
 	ret := _m.Called(allocationID, ctx, command, tty, stdin, stdout, stderr)
 
 	var r0 int
@@ -101,7 +122,7 @@ func (_m *ExecutorApiMock) ExecuteCommand(allocationID string, ctx context.Conte
 }
 
 // JobScale provides a mock function with given fields: jobId
-func (_m *ExecutorApiMock) JobScale(jobId string) (uint, error) {
+func (_m *ExecutorAPIMock) JobScale(jobId string) (uint, error) {
 	ret := _m.Called(jobId)
 
 	var r0 uint
@@ -122,7 +143,7 @@ func (_m *ExecutorApiMock) JobScale(jobId string) (uint, error) {
 }
 
 // LoadJobList provides a mock function with given fields:
-func (_m *ExecutorApiMock) LoadJobList() ([]*api.JobListStub, error) {
+func (_m *ExecutorAPIMock) LoadJobList() ([]*api.JobListStub, error) {
 	ret := _m.Called()
 
 	var r0 []*api.JobListStub
@@ -144,13 +165,13 @@ func (_m *ExecutorApiMock) LoadJobList() ([]*api.JobListStub, error) {
 	return r0, r1
 }
 
-// LoadRunners provides a mock function with given fields: jobId
-func (_m *ExecutorApiMock) LoadRunners(jobId string) ([]string, error) {
-	ret := _m.Called(jobId)
+// LoadRunners provides a mock function with given fields: jobID
+func (_m *ExecutorAPIMock) LoadRunners(jobID string) ([]string, error) {
+	ret := _m.Called(jobID)
 
 	var r0 []string
 	if rf, ok := ret.Get(0).(func(string) []string); ok {
-		r0 = rf(jobId)
+		r0 = rf(jobID)
 	} else {
 		if ret.Get(0) != nil {
 			r0 = ret.Get(0).([]string)
@@ -159,7 +180,7 @@ func (_m *ExecutorApiMock) LoadRunners(jobId string) ([]string, error) {
 
 	var r1 error
 	if rf, ok := ret.Get(1).(func(string) error); ok {
-		r1 = rf(jobId)
+		r1 = rf(jobID)
 	} else {
 		r1 = ret.Error(1)
 	}
@@ -167,13 +188,13 @@ func (_m *ExecutorApiMock) LoadRunners(jobId string) ([]string, error) {
 	return r0, r1
 }
 
-// MonitorEvaluation provides a mock function with given fields: evalID, ctx
-func (_m *ExecutorApiMock) MonitorEvaluation(evalID string, ctx context.Context) error {
-	ret := _m.Called(evalID, ctx)
+// MonitorEvaluation provides a mock function with given fields: evaluationID, ctx
+func (_m *ExecutorAPIMock) MonitorEvaluation(evaluationID string, ctx context.Context) error {
+	ret := _m.Called(evaluationID, ctx)
 
 	var r0 error
 	if rf, ok := ret.Get(0).(func(string, context.Context) error); ok {
-		r0 = rf(evalID, ctx)
+		r0 = rf(evaluationID, ctx)
 	} else {
 		r0 = ret.Error(0)
 	}
@@ -182,7 +203,7 @@ func (_m *ExecutorApiMock) MonitorEvaluation(evalID string, ctx context.Context)
 }
 
 // RegisterNomadJob provides a mock function with given fields: job
-func (_m *ExecutorApiMock) RegisterNomadJob(job *api.Job) (string, error) {
+func (_m *ExecutorAPIMock) RegisterNomadJob(job *api.Job) (string, error) {
 	ret := _m.Called(job)
 
 	var r0 string
@@ -203,7 +224,7 @@ func (_m *ExecutorApiMock) RegisterNomadJob(job *api.Job) (string, error) {
 }
 
 // SetJobScale provides a mock function with given fields: jobId, count, reason
-func (_m *ExecutorApiMock) SetJobScale(jobId string, count uint, reason string) error {
+func (_m *ExecutorAPIMock) SetJobScale(jobId string, count uint, reason string) error {
 	ret := _m.Called(jobId, count, reason)
 
 	var r0 error
@@ -217,7 +238,7 @@ func (_m *ExecutorApiMock) SetJobScale(jobId string, count uint, reason string)
 }
 
 // WatchAllocations provides a mock function with given fields: ctx, onNewAllocation, onDeletedAllocation
-func (_m *ExecutorApiMock) WatchAllocations(ctx context.Context, onNewAllocation AllocationProcessor, onDeletedAllocation AllocationProcessor) error {
+func (_m *ExecutorAPIMock) WatchAllocations(ctx context.Context, onNewAllocation AllocationProcessor, onDeletedAllocation AllocationProcessor) error {
 	ret := _m.Called(ctx, onNewAllocation, onDeletedAllocation)
 
 	var r0 error
@@ -231,7 +252,7 @@ func (_m *ExecutorApiMock) WatchAllocations(ctx context.Context, onNewAllocation
 }
 
 // init provides a mock function with given fields: nomadURL, nomadNamespace
-func (_m *ExecutorApiMock) init(nomadURL *url.URL, nomadNamespace string) error {
+func (_m *ExecutorAPIMock) init(nomadURL *url.URL, nomadNamespace string) error {
 	ret := _m.Called(nomadURL, nomadNamespace)
 
 	var r0 error
@@ -245,7 +266,7 @@ func (_m *ExecutorApiMock) init(nomadURL *url.URL, nomadNamespace string) error
 }
 
 // loadRunners provides a mock function with given fields: jobId
-func (_m *ExecutorApiMock) loadRunners(jobId string) ([]*api.AllocationListStub, error) {
+func (_m *ExecutorAPIMock) loadRunners(jobId string) ([]*api.AllocationListStub, error) {
 	ret := _m.Called(jobId)
 
 	var r0 []*api.AllocationListStub
diff --git a/nomad/nomad.go b/nomad/nomad.go
index 62d71a2..a102db1 100644
--- a/nomad/nomad.go
+++ b/nomad/nomad.go
@@ -6,7 +6,9 @@ import (
 	"fmt"
 	nomadApi "github.com/hashicorp/nomad/api"
 	"github.com/hashicorp/nomad/nomad/structs"
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/config"
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/logging"
+	"io"
 	"net/url"
 	"time"
 )
@@ -36,6 +38,12 @@ type ExecutorAPI interface {
 	// WatchAllocations listens on the Nomad event stream for allocation events.
 	// Depending on the incoming event, any of the given function is executed.
 	WatchAllocations(ctx context.Context, onNewAllocation, onDeletedAllocation AllocationProcessor) error
+
+	// ExecuteCommand executes the given command in the allocation with the given id.
+	// It writes the output of the command to stdout/stderr and reads input from stdin.
+	// If tty is true, the command will run with a tty.
+	ExecuteCommand(allocationID string, ctx context.Context, command []string, tty bool,
+		stdin io.Reader, stdout, stderr io.Writer) (int, error)
 }
 
 // APIClient implements the ExecutorAPI interface and can be used to perform different operations on the real
@@ -203,3 +211,63 @@ func checkEvaluation(eval *nomadApi.Evaluation) (err error) {
 	}
 	return err
 }
+
+// nullReader is a struct that implements the io.Reader interface and returns nothing when reading
+// from it.
+type nullReader struct{}
+
+func (r nullReader) Read(_ []byte) (int, error) {
+	return 0, nil
+}
+
+// ExecuteCommand executes the given command in the given allocation.
+// If tty is true, Nomad would normally write stdout and stderr of the command
+// both on the stdout stream. However, if the InteractiveStderr server config option is true,
+// we make sure that stdout and stderr are split correctly.
+func (a *APIClient) ExecuteCommand(allocationID string,
+	ctx context.Context, command []string, tty bool,
+	stdin io.Reader, stdout, stderr io.Writer) (int, error) {
+	if tty && config.Config.Server.InteractiveStderr {
+		return a.executeCommandInteractivelyWithStderr(allocationID, ctx, command, stdin, stdout, stderr)
+	}
+	return a.apiQuerier.Execute(allocationID, ctx, command, tty, stdin, stdout, stderr)
+}
+
+func (a *APIClient) executeCommandInteractivelyWithStderr(allocationID string, ctx context.Context,
+	command []string, stdin io.Reader, stdout, stderr io.Writer) (int, error) {
+	// Use current nano time to make the stderr fifo kind of unique.
+	currentNanoTime := time.Now().UnixNano()
+	// We expect the command to be like []string{..., "sh", "-c", "my-command"}.
+	oldCommand := command[len(command)-1]
+	// Take the last command which is the one to be executed and wrap it to redirect stderr.
+	command[len(command)-1] = wrapCommandForStderrFifo(currentNanoTime, oldCommand)
+
+	stderrExitChan := make(chan int)
+	go func() {
+		// Catch stderr in separate execution.
+		exit, err := a.Execute(allocationID, ctx, stderrFifoCommand(currentNanoTime), true, nullReader{}, stderr, io.Discard)
+		if err != nil {
+			log.WithError(err).WithField("runner", allocationID).Warn("Stderr task finished with error")
+		}
+		stderrExitChan <- exit
+	}()
+
+	exit, err := a.Execute(allocationID, ctx, command, true, stdin, stdout, io.Discard)
+
+	// Wait until the stderr catch command finished to make sure we receive all output.
+	<-stderrExitChan
+	return exit, err
+}
+
+const (
+	stderrFifoCommandFormat    = "mkfifo /tmp/stderr_%d.fifo && cat /tmp/stderr_%d.fifo"
+	stderrWrapperCommandFormat = "until [ -e /tmp/stderr_%d.fifo ]; do sleep 0.01; done; (%s) 2> /tmp/stderr_%d.fifo"
+)
+
+func stderrFifoCommand(id int64) []string {
+	return []string{"sh", "-c", fmt.Sprintf(stderrFifoCommandFormat, id, id)}
+}
+
+func wrapCommandForStderrFifo(id int64, command string) string {
+	return fmt.Sprintf(stderrWrapperCommandFormat, id, command, id)
+}
diff --git a/runner/manager.go b/runner/manager.go
index 41c2a0d..2dff852 100644
--- a/runner/manager.go
+++ b/runner/manager.go
@@ -184,7 +184,7 @@ func (m *NomadRunnerManager) refreshEnvironment(id EnvironmentID) {
 		}
 		jobScale, err := m.apiClient.JobScale(string(job.jobID))
 		if err != nil {
-			log.WithError(err).Printf("Failed get allocation count")
+			log.WithError(err).WithField("job", string(job.jobID)).Printf("Failed get allocation count")
 			break
 		}
 		additionallyNeededRunners := int(job.desiredIdleRunnersCount) - job.idleRunners.Length()
diff --git a/tests/e2e/runners_test.go b/tests/e2e/runners_test.go
index 0919848..28cd99c 100644
--- a/tests/e2e/runners_test.go
+++ b/tests/e2e/runners_test.go
@@ -112,7 +112,7 @@ func (s *E2ETestSuite) TestCopyFilesRoute() {
 		s.Equal(http.StatusNoContent, resp.StatusCode)
 
 		s.Run("File content can be printed on runner", func() {
-			s.Equal(tests.DefaultFileContent, s.PrintContentOfFileOnRunner(runnerID, tests.DefaultFileName))
+			s.assertFileContent(runnerID, tests.DefaultFileName, tests.DefaultFileContent)
 		})
 	})
 
@@ -134,11 +134,11 @@ func (s *E2ETestSuite) TestCopyFilesRoute() {
 
 		s.Run("File content of file with relative path can be printed on runner", func() {
 			// the print command is executed in the context of the default working directory of the container
-			s.Equal(relativeFileContent, s.PrintContentOfFileOnRunner(runnerID, relativeFilePath))
+			s.assertFileContent(runnerID, relativeFilePath, relativeFileContent)
 		})
 
 		s.Run("File content of file with absolute path can be printed on runner", func() {
-			s.Equal(absoluteFileContent, s.PrintContentOfFileOnRunner(runnerID, absoluteFilePath))
+			s.assertFileContent(runnerID, absoluteFilePath, absoluteFileContent)
 		})
 	})
 
@@ -152,7 +152,9 @@ func (s *E2ETestSuite) TestCopyFilesRoute() {
 		s.Equal(http.StatusNoContent, resp.StatusCode)
 
 		s.Run("File content can no longer be printed", func() {
-			s.Contains(s.PrintContentOfFileOnRunner(runnerID, tests.DefaultFileName), "No such file or directory")
+			stdout, stderr := s.PrintContentOfFileOnRunner(runnerID, tests.DefaultFileName)
+			s.Equal("", stdout)
+			s.Contains(stderr, "No such file or directory")
 		})
 	})
 
@@ -168,7 +170,7 @@ func (s *E2ETestSuite) TestCopyFilesRoute() {
 		_ = resp.Body.Close()
 
 		s.Run("File content can be printed on runner", func() {
-			s.Equal(tests.DefaultFileContent, s.PrintContentOfFileOnRunner(runnerID, tests.DefaultFileName))
+			s.assertFileContent(runnerID, tests.DefaultFileName, tests.DefaultFileContent)
 		})
 	})
 
@@ -191,7 +193,7 @@ func (s *E2ETestSuite) TestCopyFilesRoute() {
 		_ = resp.Body.Close()
 
 		s.Run("File content can be printed on runner", func() {
-			s.Equal(string(newFileContent), s.PrintContentOfFileOnRunner(runnerID, tests.DefaultFileName))
+			s.assertFileContent(runnerID, tests.DefaultFileName, string(newFileContent))
 		})
 	})
 
@@ -208,7 +210,13 @@ func (s *E2ETestSuite) TestCopyFilesRoute() {
 	})
 }
 
-func (s *E2ETestSuite) PrintContentOfFileOnRunner(runnerId string, filename string) string {
+func (s *E2ETestSuite) assertFileContent(runnerID, fileName string, expectedContent string) {
+	stdout, stderr := s.PrintContentOfFileOnRunner(runnerID, fileName)
+	s.Equal(expectedContent, stdout)
+	s.Equal("", stderr)
+}
+
+func (s *E2ETestSuite) PrintContentOfFileOnRunner(runnerId string, filename string) (string, string) {
 	webSocketURL, _ := ProvideWebSocketURL(&s.Suite, runnerId, &dto.ExecutionRequest{Command: fmt.Sprintf("cat %s", filename)})
 	connection, _ := ConnectToWebSocket(webSocketURL)
 
@@ -216,6 +224,6 @@ func (s *E2ETestSuite) PrintContentOfFileOnRunner(runnerId string, filename stri
 	s.Require().Error(err)
 	s.Equal(&websocket.CloseError{Code: websocket.CloseNormalClosure}, err)
 
-	stdout, _, _ := helpers.WebSocketOutputMessages(messages)
-	return stdout
+	stdout, stderr, _ := helpers.WebSocketOutputMessages(messages)
+	return stdout, stderr
 }
diff --git a/tests/e2e/websocket_test.go b/tests/e2e/websocket_test.go
index 5151535..6392ebe 100644
--- a/tests/e2e/websocket_test.go
+++ b/tests/e2e/websocket_test.go
@@ -65,7 +65,6 @@ func (s *E2ETestSuite) TestOutputToStdout() {
 }
 
 func (s *E2ETestSuite) TestOutputToStderr() {
-	s.T().Skip("known bug causing all output to be written to stdout (even if it should be written to stderr)")
 	connection, err := ProvideWebSocketConnection(&s.Suite, &dto.ExecutionRequest{Command: "cat -invalid"})
 	s.Require().NoError(err)
 
@@ -74,8 +73,9 @@ func (s *E2ETestSuite) TestOutputToStderr() {
 	s.Equal(&websocket.CloseError{Code: websocket.CloseNormalClosure}, err)
 
 	controlMessages := helpers.WebSocketControlMessages(messages)
+	s.Require().Equal(2, len(controlMessages))
 	s.Require().Equal(&dto.WebSocketMessage{Type: dto.WebSocketMetaStart}, controlMessages[0])
-	s.Require().Equal(&dto.WebSocketMessage{Type: dto.WebSocketExit}, controlMessages[1])
+	s.Require().Equal(&dto.WebSocketMessage{Type: dto.WebSocketExit, ExitCode: 1}, controlMessages[1])
 
 	stdout, stderr, errors := helpers.WebSocketOutputMessages(messages)
 	s.NotContains(stdout, "cat: invalid option", "Stdout should not contain the error")