Modal logo
IntroductionCustom container images Defining ImagesUsing existing container imagesFast pull from registryGPUs and other resources GPU accelerationUsing CUDA on ModalReserving CPU and memoryScaling out Scaling outInput concurrencyBatch processingJob queuesDynamic batching (beta)Multi-node clusters (beta)Deployment Apps, Functions, and entrypointsManaging deploymentsInvoking deployed functionsContinuous deploymentRunning untrusted code in FunctionsModal Sandboxes SandboxesRunning commandsNetworking and securityFile accessSnapshotsModal NotebooksSecrets and environment variables SecretsEnvironment variablesScheduling and cron jobsWeb endpoints Web endpointsStreaming endpointsWeb endpoint URLsRequest timeoutsProxy Auth TokensNetworking TunnelsProxies (beta)Cluster networkingData sharing and storage Passing local dataVolumesStoring model weightsCloud bucket mountsDictsQueuesDataset ingestionPerformance Cold start performanceMemory SnapshotHigh-performance LLM inferenceGeographic latencyReliability and robustness Failures and retriesPreemptionTimeoutsGPU healthTroubleshootingSecurity and privacyIntegrations Using OIDC to authenticate with external servicesConnecting Modal to your Datadog accountConnecting Modal to your OpenTelemetry providerOkta SSOCustom SAML SSOSlack notifications (beta)Workspace & account settings WorkspacesEnvironmentsModal user account setupService usersBillingOther topics JavaScript/Go SDKsModal 1.0 migration guideFile and project structureDeveloping and debuggingDeveloping Modal code with LLMsJupyter notebooksAsynchronous API usageGlobal variablesRegion selectionContainer lifecycle hooksParametrized functionsS3 Gateway endpointsGPU Metrics

Running commands in Sandboxes

Once you have created a Sandbox, you can run commands inside it using the Sandbox.exec method.

Sandbox.exec returns a ContainerProcess object, which allows access to the process’s stdout, stderr, and stdin. The timeout parameter ensures that the exec command will run for at most timeout seconds.

Input 

The Sandbox and ContainerProcess stdin handles are StreamWriter objects. This object supports flushing writes with both synchronous and asynchronous APIs:

Output 

The Sandbox and ContainerProcess stdout and stderr handles are StreamReader objects. These objects support reading from the stream in both synchronous and asynchronous manners. These handles also respect the timeout given to Sandbox.exec.

To read from a stream after the underlying process has finished, you can use the read method, which blocks until the process finishes and returns the entire output stream.

To stream output, take advantage of the fact that stdout and stderr are iterable:

Stream types 

By default, all streams are buffered in memory, waiting to be consumed by the client. You can control this behavior with the stdout and stderr parameters. These parameters are conceptually similar to the stdout and stderr parameters of the subprocess module.