Sandbox Compute Drivers

The gateway’s configured compute driver determines how OpenShell creates each sandbox. The CLI workflow stays the same across drivers: you create, connect to, inspect, stop, start, and delete sandboxes through the gateway API.

Most compute drivers run the OpenShell supervisor inside the sandbox workload. The supervisor launches the agent process, applies policy, routes egress through the proxy, injects configured credentials, and maintains the gateway session. A driver may instead set driver_reports_runtime_readiness. In that mode, driver-reported readiness does not require a supervisor session. The canonical create-time policy is part of DriverSandboxSpec; a driver that enforces policy outside the standard supervisor fetches later revisions through the existing sandbox configuration API. The Windows MXC driver reports its own readiness.

Stop stops compute but retains the sandbox record and the driver’s persistent workspace boundary. Start reactivates the same driver resource. Delete remains independent and removes compute plus driver-owned persistent state. While a sandbox is stopped, gateway access paths and exposed services remain unavailable.

Restarting the gateway preserves this intent. The gateway does not stop Docker or Podman containers during shutdown. At startup it sends idempotent start requests for Docker, Podman, and MicroVM sandboxes that were intended to run; already-running resources are unchanged, retained stopped compute is restarted, and explicitly stopped sandboxes remain stopped. Kubernetes workloads continue running independently of the gateway process.

The gateway forwards one exact, persisted main-process specification to every driver. Drivers serialize that specification in OPENSHELL_MAIN_PROCESS_SPEC; they do not install an idle sleep workload or reconstruct argv with shell parsing. Runtime restart policies are disabled so an exited canonical process remains a terminal sandbox result. Exit code zero produces Completed; a nonzero or signal-normalized exit produces Error with the exact exit code. Driver and supervisor failures remain Error.

Build with Selected Compute Drivers

Source builds of openshell-gateway can include any subset of the Docker, Podman, Kubernetes, VM, and MXC drivers. Enable the corresponding compute-driver-docker, compute-driver-podman, compute-driver-kubernetes, compute-driver-vm, or compute-driver-mxc Cargo features. For example, build a Docker-only gateway with telemetry support:

cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-docker

On Windows, select only MXC with:

cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-mxc,bundled-z3

The default in-tree-compute-drivers feature retains the full platform driver set, including MXC on Windows. MXC links only on Windows. The other four features link drivers on non-Windows platforms; on Windows they install registrations that report the driver as unsupported. A build with no default features and no driver features connects to external drivers only. Auto-detection probes only compiled registrations. To select a driver omitted from a custom build, configure its external socket_path as described below.

Configure a Compute Driver

Configure the compute driver on the gateway. Current releases accept one driver per gateway. Set the singular compute_driver key in the gateway TOML file:

[openshell.gateway]
compute_driver = "docker"

Reserved built-in values are docker, podman, kubernetes, vm, and mxc. The mxc driver is available only in native Windows gateway builds. Non-reserved names select an extension driver and require a socket_path in [openshell.drivers.<name>].

When compute_driver is unset, the gateway auto-detects Kubernetes, then Podman, then Docker. Docker must respond on a known API socket. Podman first probes known API sockets and then asks the podman CLI for the active native or machine-backed socket. The VM driver is never auto-detected; configure it explicitly with compute_driver = "vm" or set OPENSHELL_COMPUTE_DRIVER=vm in the launch environment.

compute_driver accepts exactly one scalar driver name. The legacy compute_drivers list is rejected by schema version 2.

Common gateway options:

Set driver-specific values such as sandbox images, callback endpoints, network names, and VM sizing in the gateway TOML file. A TLS-enabled gateway-managed Docker, Podman, or VM driver requires a complete guest_tls_ca, guest_tls_cert, and guest_tls_key bundle in [openshell.gateway]; package-managed local TLS supplies it automatically. Driver tables reject those gateway-owned fields. Kubernetes projects guest TLS through a Secret instead. See the Gateway Configuration File reference for the full schema and migration steps.

Extension drivers use the same compute_driver.proto gRPC surface as the managed VM driver. For an out-of-tree driver, choose a driver name and point the gateway at the Unix socket the operator has already provisioned:

[openshell.gateway]
compute_driver = "kyma"
[openshell.drivers.kyma]
socket_path = "/run/openshell/kyma.sock"

For a launch-time socket override, pass the selected driver name with the socket path. The endpoint replaces normal driver construction for that name, including canonical built-in names:

openshell-gateway --compute-driver kyma --compute-driver-socket /run/openshell/kyma.sock
openshell-gateway --compute-driver docker --compute-driver-socket /run/openshell/docker.sock

The gateway connects to the operator-provided endpoint; it does not provision or supervise the remote driver. The operator must protect the socket so only the gateway uid can access it.

Sandbox create supports --cpu and --memory for per-sandbox compute sizing. Docker and Podman apply them as runtime limits. Kubernetes applies them as both container requests and limits. The VM driver accepts the fields but currently ignores them.

Sandbox create also accepts experimental driver-owned config through --driver-config-json. The value is a JSON object keyed by driver name. The gateway forwards only the block for the active driver, so a Kubernetes gateway receives the kubernetes object from a value such as:

Nested keys inside each driver block use snake_case. The top-level envelope keys are driver names, such as kubernetes, and are not part of the nested schema.

openshell sandbox create \
  --driver-config-json '{"kubernetes":{"pod":{"runtime_class_name":"kata-containers","priority_class_name":"batch-low"}}}' \
  -- claude

Driver config is for fields without a stable public flag. Prefer --cpu, --memory, and --gpu for supported resource intent. When --gpu is present without a count, OpenShell treats it as a request for one GPU. Pass --gpu COUNT when requesting more than one GPU.

Kubernetes maps the GPU count to the nvidia.com/gpu pod resource limit. Docker and Podman satisfy count-only GPU requests by selecting the requested number of NVIDIA CDI devices from the local CDI inventory in round-robin order. The drivers refresh the CDI inventory before validating or creating the sandbox, so CDI devices added or removed after gateway start can affect later creates. On WSL2 all-only runtimes, Docker or Podman can use nvidia.com/gpu=all as a compatibility fallback, where it counts as one selectable device.

Exact GPU device selection remains driver-owned and requires --gpu. Docker and Podman accept cdi_devices as opaque CDI device names; replace the top-level docker key with podman when using the Podman driver, for example {"docker":{"cdi_devices":["nvidia.com/gpu=0"]}}. Explicit CDI device lists must not contain duplicates, and their length must match the effective GPU count. A single exact CDI device is compatible with the default --gpu request. The VM driver accepts gpu_device_ids, for example {"vm":{"gpu_device_ids":["0000:2d:00.0"]}}; the current VM implementation accepts at most one entry and allows either --gpu or --gpu 1 when gpu_device_ids is set.

Resource Capability Reporting

API clients can read each configured driver’s static resource request support from the protected GetGatewayInfo response. The capability response describes which request forms a driver implements. It does not report live resource inventory, availability, or scheduling capacity, so a supported request can still fail when the selected runtime cannot provide the resource.

CPU and memory capabilities report whether the driver enforces a resource limit. GPU capabilities report whether the driver accepts a default GPU request and an explicit GPU count. An omitted resource_capabilities message, or an omitted CPU, memory, or GPU capability, means the driver did not report that capability. A reported false value means that request form is unsupported.

For Kubernetes, pod.runtime_class_name maps to PodSpec runtimeClassName. It overrides the gateway’s configured default runtime class for that sandbox, while a typed SandboxTemplate.runtime_class_name value from the API still takes precedence.

Docker and Podman report the address through which their sandboxes can reach the gateway. If the primary listener covers that address, the gateway reuses it and sandbox JWT authentication restricts the supervisor to its callback RPC allowlist. If the primary listener is not reachable through that address, the gateway creates an additional callback-only listener. Use the primary endpoint for CLI, administrator, health, reflection, provider management, and HTTP requests. A PermissionDenied response from an additional callback-only listener is expected for those requests. Do not broaden the primary listener to 0.0.0.0 solely to make sandbox callbacks reachable.

Docker Driver

Docker-backed sandboxes run as containers on the gateway host. Use Docker for local development, single-machine gateways, and hosts that already use Docker Desktop or Docker Engine.

The gateway talks to the Docker daemon to create sandbox containers.

Docker Desktop and compatible macOS runtimes route host.openshell.internal through an IPv4 host-gateway alias. The gateway reuses an IPv4 primary listener that already covers loopback. Otherwise, the Docker driver requests a separate 127.0.0.1:<gateway-port> callback-only listener.

For maintainer-level implementation details, refer to the Docker driver README.

Select Docker with compute_driver = "docker" in [openshell.gateway]. Configure Docker driver values such as socket_path, grpc_endpoint, network_name, sandbox_label, supervisor_bin, supervisor_image, image_pull_policy, ssh_socket_path, and sandbox_pids_limit in [openshell.drivers.docker]. When socket_path is unset, the driver uses the same responsive local socket selected by auto-detection. An explicitly selected Docker driver falls back to /var/run/docker.sock when no candidate responds.

When operating openshell-driver-docker as an external driver, set OPENSHELL_OTLP_ENDPOINT to export its spans. The driver continues W3C trace context from gateway RPCs and reports as openshell-driver-docker.

Stop stops the existing Docker container without removing its writable layer or attached volumes. Start starts that same container. A durably stopped container stays stopped across gateway restart, and delete remains responsible for removing it. Graceful gateway shutdown stops running-intent Docker containers through the driver RPC without recording an explicit sandbox stop. On startup, the gateway reconciles that retained intent with an idempotent start request. Explicitly stopped sandboxes remain stopped.

For GPU-backed Docker sandboxes, configure Docker CDI before starting the gateway so OpenShell can detect the daemon capability.

Docker Driver Config Mounts

Docker driver config accepts user-supplied volume and tmpfs mounts. It also accepts bind mounts when [openshell.drivers.docker] sets enable_bind_mounts = true in gateway.toml. See Docker’s storage documentation for more information. Docker local-driver named volumes created with bind options also expose gateway-host paths, so OpenShell treats them like bind mounts and requires enable_bind_mounts = true.

Use a volume mount for existing Docker named volumes:

docker volume create openshell-work
openshell sandbox create \
  --driver-config-json '{"docker":{"mounts":[{"type":"volume","source":"openshell-work","target":"/sandbox/work","read_only":false}]}}' \
  -- claude

Use a bind mount only after enabling it in the Docker driver table:

[openshell.drivers.docker]
enable_bind_mounts = true

openshell sandbox create \
  --driver-config-json '{"docker":{"mounts":[{"type":"bind","source":"/srv/openshell/work","target":"/sandbox/work","read_only":false}]}}' \
  -- claude

Docker mount schema:

OpenShell rejects mount source, target, and Docker volume subpath values with surrounding whitespace. OpenShell also rejects mount targets that replace the workspace root or container root, or contain or are contained by the configured SSH socket or reserved /opt/openshell, /etc/openshell, /etc/openshell-tls, /run/openshell, /run/openshell-sidecar, and network namespace roots. These checks do not make host bind mounts safe.

Podman Driver

Podman-backed sandboxes run as rootless containers on the gateway host. Use Podman for Linux workstation workflows that avoid a rootful Docker daemon.

The gateway talks to the Podman API socket. The Podman driver requires Podman 5.x, cgroups v2, rootless networking, and an active Podman user socket. When socket_path is not set, the driver probes known socket paths, then uses the podman CLI to resolve the active native or machine-backed connection. It fails to start if neither method finds a socket.

For maintainer-level implementation details, refer to the Podman driver README and Podman networking notes.

Select Podman with compute_driver = "podman" in [openshell.gateway]. Configure Podman driver values such as socket_path, network_name, supervisor_image, stop_timeout_secs, image_pull_policy, grpc_endpoint, host_gateway_ip, ssh_socket_path, and sandbox_pids_limit in [openshell.drivers.podman].

macOS Podman Socket Path

On macOS, Homebrew-installed Podman does not create the default socket path that the driver probes (~/.local/share/containers/podman/machine/podman.sock). The actual API socket lives under /var/folders/ in a path that macOS can rotate after a reboot.

If the gateway fails with Podman socket not found; is podman machine running? while podman machine list shows a running machine, set the OPENSHELL_PODMAN_SOCKET environment variable to the dynamic socket path:

export OPENSHELL_PODMAN_SOCKET="$(podman machine inspect --format '{{.ConnectionInfo.PodmanSocket.Path}}')"

Add this to your shell profile or gateway launch environment so it resolves correctly after each reboot. Alternatively, set socket_path in [openshell.drivers.podman] to the current path, but note that the path may change when macOS rotates /var/folders/.

Podman sandboxes default to a 45-second graceful stop window before Podman escalates from SIGTERM to SIGKILL. Set stop_timeout_secs in gateway config, or OPENSHELL_STOP_TIMEOUT for the standalone driver, when a local runtime needs a different teardown window.

Stop stops the existing Podman container while retaining its named workspace volume and driver-owned secrets. Start starts the same container. Delete is the operation that removes the container and named volume. Graceful gateway shutdown stops running-intent Podman containers through the driver RPC without recording an explicit sandbox stop. On startup, the gateway reconciles that retained intent with an idempotent start request while leaving explicitly stopped sandboxes alone.

For proxy-required networks, the Podman driver also accepts the corporate egress proxy keys https_proxy, no_proxy, proxy_auth_file, proxy_auth_allow_insecure, and proxy_connect_by_hostname. The supervisor chains policy-approved TLS tunnels through the proxy with HTTP CONNECT instead of dialing destinations directly. See the Gateway Configuration File reference for the full contract, including the cleartext-credential acknowledgement and the validated-IP CONNECT behavior.

Podman preserves its runtime-selected AppArmor profile when app_armor_profile is omitted. Set Unconfined explicitly only when the supervisor’s mount setup requires it. Explicit RuntimeDefault and Localhost/<profile> selections fail startup when Podman reports that AppArmor is unavailable.

On macOS with podman machine, the driver uses gvproxy’s host-loopback IP, 192.168.127.254, for sandbox host aliases by default. Set host_gateway_ip only when your Podman machine uses a non-standard host-loopback address. On Linux, an empty host_gateway_ip keeps Podman’s host-gateway resolver behavior. Direct local callbacks from rootless Podman require Podman to report the pasta network helper. Slirp4netns, other helpers, and Podman versions that do not report their helper require an explicitly remote grpc_endpoint; otherwise the gateway fails startup rather than leaving sandbox callbacks unreachable. Rootful Podman continues to use the configured network’s bridge gateway address.

Podman Driver Config Mounts

Podman driver config accepts user-supplied volume, tmpfs, and image mounts. It also accepts bind mounts when [openshell.drivers.podman] sets enable_bind_mounts = true in gateway.toml. Podman local-driver named volumes created with bind options also expose gateway-host paths, so OpenShell treats them like bind mounts and requires enable_bind_mounts = true. Host bind mounts expose gateway host paths to sandbox requests, so they are disabled by default.

Use a volume mount for existing Podman named volumes:

podman volume create openshell-work
openshell sandbox create \
  --driver-config-json '{"podman":{"mounts":[{"type":"volume","source":"openshell-work","target":"/sandbox/work","read_only":false}]}}' \
  -- claude

Use a bind mount only after enabling it in the Podman driver table:

[openshell.drivers.podman]
enable_bind_mounts = true

openshell sandbox create \
  --driver-config-json '{"podman":{"mounts":[{"type":"bind","source":"/srv/openshell/work","target":"/sandbox/work","read_only":false}]}}' \
  -- claude

Podman mount schema:

Podman volume and image mounts do not support subpath in OpenShell driver config, and OpenShell rejects subpath for those mount types. OpenShell rejects mount source and target values with surrounding whitespace. OpenShell also rejects mount targets that replace the workspace root, container root, supervisor files, /etc/openshell, /etc/openshell-tls, authentication material, or network namespace paths. These checks do not make host bind mounts safe.

MicroVM Driver

MicroVM-backed sandboxes run inside VM-backed isolation instead of a container boundary. Use MicroVM when workloads need a VM boundary instead of a local container boundary.

The gateway uses the VM compute driver to create VM-backed sandboxes. MicroVM requires host virtualization support. It uses libkrun with Apple’s Hypervisor framework on macOS, KVM on Linux, and QEMU for GPU-backed sandboxes on Linux.

The VM driver boots a cached immutable bootstrap ext4 root disk. When the requested sandbox image differs from the bootstrap image, the driver stages the registry image as an OCI layout, unpacks it inside a bootstrap VM with umoci, and caches the prepared image disk by image identity. Each sandbox receives that prepared disk read-only plus its own writable overlay.ext4 disk for /, including /sandbox writes and runtime TLS material. The overlay persists for the sandbox lifetime and is deleted with the sandbox state directory.

VM sandbox creation follows the same progress model as Kubernetes-backed sandboxes. The gateway accepts the sandbox, then the VM driver publishes watch events while it resolves the image, prepares or reuses the bootstrap and prepared image caches, creates the writable overlay, and starts the VM launcher.

On graceful gateway shutdown, the gateway stops running-intent VMs through the driver RPC while retaining their launch records and writable overlays. On restart, the gateway starts a fresh VM driver process and reconciles the retained intent through the same idempotent start request used by the local container drivers. Running-intent VMs restart with their existing overlay.ext4, while explicitly stopped VMs remain stopped.

Stopped VM state directories contain a marker that prevents startup from launching the VM. The driver retains sandbox.pb, overlay.ext4, and extension state, then removes the marker and restores the same overlay on start.

For maintainer-level implementation details, refer to the VM driver README.

Enable the VM Driver

The VM driver is opt-in. Release packages can install openshell-driver-vm, but the gateway does not select it unless you configure the driver explicitly.

Enable VM by setting compute_driver = "vm" in the gateway TOML file:

[openshell.gateway]
compute_driver = "vm"

For a launch-time override, set OPENSHELL_COMPUTE_DRIVER=vm in the gateway environment and restart the service.

Configure VM driver values such as grpc_endpoint, driver_dir, state_dir, default_image, bootstrap_image, vcpus, mem_mib, overlay_disk_mib, and krun_log_level in [openshell.drivers.vm]. The VM state_dir stores overlay disks, console logs, runtime state, image-rootfs cache, and the private run/compute-driver.sock socket. The VM socket path is managed by the gateway and is not configurable through remote endpoint settings.

The gateway starts openshell-driver-vm over a private Unix socket and passes its process ID so the driver can reject unexpected local clients. The driver’s standalone TCP listener is disabled unless --allow-unauthenticated-tcp is set for local development.

Scripts that invoke the experimental standalone driver directly must use --grpc-endpoint and the --upstream-proxy* option family. Schema v2 removes the previous --openshell-endpoint, --https-proxy, --no-proxy, and --proxy-* spellings; gateway-managed deployments do not use those options directly.

Local image resolution

The VM driver resolves sandbox images from a local container engine before falling back to registry pulls. It tries Docker first, then uses the same Podman socket discovery as the Podman driver. On Linux with Podman, enable the API socket so the driver can find local images:

systemctl --user start podman.socket

Host Firewall

The VM driver creates nftables rules on the host for each sandbox VM’s TAP network interface. These rules provide NAT for VM connectivity and defense-in-depth isolation: unsolicited inbound connections to the VM are dropped, and the VM can only reach the gateway port on the host. Primary security enforcement (proxy-only egress and bypass detection) is handled by the sandbox supervisor inside the VM guest.

On hosts with restrictive firewalls (e.g. firewalld), the host firewall may additionally block VM traffic that the driver’s rules accept. If VM sandboxes cannot reach the network, verify that the host firewall allows forwarding and input for vmtap-* interfaces. See the VM driver README for details.

Corporate Proxy Egress

For proxy-required networks, the VM driver accepts the same corporate egress proxy keys as the Podman driver: https_proxy, no_proxy, proxy_auth_file, proxy_auth_allow_insecure, proxy_connect_by_hostname, and proxy_ca_bundle. The in-guest supervisor chains policy-approved TLS tunnels through the proxy with HTTP CONNECT instead of dialing destinations directly.

The settings reach the guest supervisor on its command line through a per-sandbox argument file the driver writes into the overlay upperdir on every launch, so a sandbox cannot select, alter, or disable the proxy from inside the guest — including through image ENV, the sandbox environment, or files baked into the image at the paths the driver uses.

A proxy on the corporate network needs no special address and works on every VM sandbox. The guest’s callback to the gateway never traverses the proxy.

A proxy on the gateway host itself works only for libkrun-backed (non-GPU) sandboxes, whose egress leaves through gvproxy: configure https_proxy = "http://host.openshell.internal:<port>" rather than a 127.0.0.1 URL, because gvproxy NATs that alias to the host’s 127.0.0.1. GPU sandboxes use the QEMU/TAP backend, where host.openshell.internal resolves to the TAP host address and the driver’s host firewall rules allow the guest to reach only the gateway port on the host. The driver rejects a gateway-host proxy URL when a sandbox launches on QEMU instead of letting every CONNECT time out, so give GPU sandboxes a proxy address routable from the guest’s masqueraded egress.

Because a microVM has no bind mounts or container secrets, the driver stages the credential (root-only) and the CA bundle into the per-sandbox overlay disk and removes them with the sandbox. See the Gateway Configuration File reference for the full contract, including the cleartext-credential acknowledgement and the validated-IP CONNECT behavior.

Kubernetes Driver

Kubernetes-backed sandboxes run as pods in the configured sandbox namespace. Use Kubernetes for shared clusters, remote compute, GPU scheduling, and operator-managed environments.

Helm deployments set Kubernetes driver values through the chart. Canonical TOML places namespace, service_account_name, and enable_user_namespaces in [openshell.drivers.kubernetes]; schema version 2 rejects their historical [openshell.gateway] locations.

For maintainer-level implementation details, refer to the Kubernetes driver README.

Managed-mode Secret copying requires the gateway ServiceAccount to create Secrets. Kubernetes RBAC cannot restrict Secret create by resource name, so the Helm chart grants cluster-wide Secret create; Secret get and patch remain limited to the explicitly configured TLS and image-pull Secret names. The driver creates copies only in gateway-owned managed namespaces. Do not reuse the gateway ServiceAccount for unrelated workloads.

In combined topology, the agent container carries the Linux capabilities needed by the supervisor for network namespace setup, Landlock filesystem policy, process privilege changes, and network policy enforcement. In sidecar topology, the agent container runs as the resolved sandbox UID/GID with no added Linux capabilities. A root init container performs the nftables setup, and the long-running binary-aware sidecar runs as UID 0, drops default capabilities, and adds SYS_PTRACE plus DAC_READ_SEARCH for workload process identity resolution through shared /proc. The sidecar.process_binary_aware_network_policy = false setting runs it as the configured non-root proxy_uid, removes both capabilities, and relaxes network policy to endpoint/L7 matching only. The network sidecar owns gateway authentication and writes local policy/provider state to the process supervisor over a local control socket, so the agent container does not mount the sandbox bootstrap token or client TLS secret in the default sidecar path. The provider environment is refreshed by the network sidecar after settings polls and streamed to the process supervisor so future child processes can see updated provider env without gateway access in the agent container. Sidecar mode keeps gateway session and SSH behavior. The process supervisor applies Landlock filesystem policy and child seccomp filters where supported, but it does not perform root-to-sandbox privilege dropping or supervisor identity mount isolation. Network policy still runs in the sidecar, and sidecar pods set shareProcessNamespace: true so the network sidecar can resolve process/binary identity through /proc/<entrypoint-pid>.

The Kubernetes driver creates namespaced agents.x-k8s.io Sandbox resources from the Kubernetes SIG Apps agent-sandbox project. It detects the served Sandbox API at runtime, caches the selected API version for the gateway process, and uses v1beta1 when available before falling back to v1alpha1, so supported Agent Sandbox installations work without version-specific operator configuration. The Agent Sandbox controller turns those resources into sandbox pods and related storage.

Stop patches the existing resource rather than deleting it. For v1beta1, the driver sets spec.operatingMode to Suspended or Running. For v1alpha1, it sets spec.replicas to 0 or 1. The Sandbox resource and its workspace PVC keep their identity across both operations. Stop returns only after the controller reports suspension and deletes the old pod, so an immediate start cannot race the prior pod’s termination.

If Agent Sandbox is upgraded in place, restart the OpenShell gateway after the controller and CRD rollout completes so the gateway can detect the served API versions again.

Kubernetes Driver Config PVC Mounts

Kubernetes driver config can mount existing PersistentVolumeClaims into the agent container. Use this when storage is provisioned outside OpenShell and a sandbox should mount selected PVC subpaths instead of using the default OpenShell-created /sandbox workspace PVC.

openshell sandbox create \
  --driver-config-json '{
    "kubernetes": {
      "volumes": [{
        "name": "user-data",
        "persistent_volume_claim": {
          "claim_name": "pvc-user-data-123",
          "read_only": false
        }
      }],
      "containers": {
        "agent": {
          "volume_mounts": [
            {
              "name": "user-data",
              "mount_path": "/sandbox/.openshell/workspace",
              "sub_path": "workspace",
              "read_only": false
            },
            {
              "name": "user-data",
              "mount_path": "/sandbox/.openshell/memory",
              "sub_path": "memory",
              "read_only": false
            }
          ]
        }
      }
    }
  }' \
  -- claude

Kubernetes PVC mount schema:

OpenShell rejects duplicate volume names, mounts that reference unknown volumes, protected mount targets, and mounts that replace OpenShell TLS, supervisor, ServiceAccount token, or SPIFFE paths. Read-write PVC access requires read_only: false on both the PVC volume and each writable mount.

Any driver-config mount under /sandbox disables the default /sandbox workspace PVC injection for that sandbox. Only the explicit mount paths persist through the external PVC; other /sandbox paths come from the current sandbox image.

Sandbox User Identity

The policy can set process.run_as_user and process.run_as_group independently. Each explicit field wins. The active compute driver supplies the identity for omitted fields.

Explicit numeric values may use any non-root Linux UID/GID from 1 through 4294967294. OpenShell rejects 0 as root and 4294967295 as the invalid identity sentinel. Low numeric identities can inherit permissions from matching accounts, files, volumes, or devices, so choose them with the same care as any other runtime identity.

Docker / Podman

Docker and Podman inspect the final image and use its OCI USER declaration as a per-field fallback. Supported forms include app, app:staff, a numeric UID whose passwd entry supplies its primary GID, and an accountless numeric pair such as 1234:1235.

The driver pins container creation to the immutable image ID it inspected. The supervisor validates any required names inside that image and preserves the declared name or numeric components for both direct and SSH children. When USER omits the group, the supervisor uses the user’s numeric primary GID. It does not modify /etc/passwd or /etc/group.

Docker also inspects OCI WorkingDir. An absolute value becomes the agent workspace; an empty, root (/), or explicit /sandbox value uses the managed /sandbox compatibility workspace. OpenShell creates and owns that compatibility workspace. Any other workdir must already exist in the immutable image without symlink components. The completed UID/GID and supplementary groups must already be able to traverse every parent and write and enter the workdir. OpenShell does not change that directory’s ownership or mode. A one-shot validator drops to that identity and uses kernel effective-access checks, including POSIX ACL grants and LSM denials. It rejects workdirs that overlap the OCI runtime namespaces under /proc, /sys, or /dev, and rejects overlap with actual OpenShell control paths. Docker checks the original image filesystem in the final supervisor and rejects image VOLUME declarations that would mask the workdir or one of its parents before validation. The resolved workspace is the cwd and HOME for direct and SSH children. The supervisor itself starts from /, so a missing or invalid workspace is handled during readiness instead of preventing the container runtime from starting it.

Sandbox creation fails before readiness if a required USER component is missing, malformed, unknown, ambiguous, or resolves to UID/GID 0. An image without USER therefore works only when policy explicitly provides both identity fields.

Kubernetes / OpenShift

The Kubernetes driver auto-detects the sandbox UID from OpenShift SCC namespace annotations:

• openshift.io/sa.scc.uid-range (format: <start>/<size>, e.g. 1000000000/10000) provides the UID.
• openshift.io/sa.scc.supplemental-groups provides the GID when present; otherwise the resolved UID is used as the GID.
• On non-OpenShift clusters, or when annotations are absent, the driver falls back to 1000.

You can override autodetection with explicit sandbox_uid / sandbox_gid config in [openshell.drivers.kubernetes]. When set, the driver skips namespace annotation lookup entirely.

The resolved UID/GID appear in:

• Supervisor container environment variables (OPENSHELL_SANDBOX_UID, OPENSHELL_SANDBOX_GID) for direct kernel-level privilege dropping without /etc/passwd lookups.
• PVC init container securityContext.runAsUser/runAsGroup/fsGroup for workspace ownership operations.

VM Driver

The VM driver preserves an image-provided sandbox account when sandbox_uid and sandbox_gid are omitted. Images without that account use UID/GID 1000. Explicit values in [openshell.drivers.vm] override the image account. Persisted overlays retain the UID/GID recorded when they were created. An unmarked overlay recovers identity from concrete overlay or prepared-image state, an explicit override, or the current image; the driver never assigns legacy 10001:10001 without persisted evidence.

Custom Images

Docker and Podman custom images do not need a baked-in "sandbox" user. Declare a non-root OCI USER, or set both process identity fields explicitly in policy. Named image users require matching account entries; a numeric UID:GID pair does not. For Docker, declare an absolute OCI WORKDIR to select the workspace. Images with no working directory, WORKDIR /, or WORKDIR /sandbox use OpenShell’s managed /sandbox compatibility workspace. For any other Docker path, create the directory in the image and grant the final process identity write and execute permission in the Dockerfile. Podman, Kubernetes/OpenShift, and VM sandboxes continue to use /sandbox.