Sandbox Compute Drivers | NVIDIA OpenShell

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, and delete sandboxes through the gateway API.

Every compute driver runs 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.

Configure a Compute Driver

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

1 [openshell.gateway]
2 compute_drivers = ["docker"]

Reserved built-in values are docker, podman, kubernetes, and vm. Non-reserved names select an extension driver and require a socket_path in [openshell.drivers.<name>].

When compute_drivers is unset, the gateway auto-detects Kubernetes, then Podman, then Docker. Local container runtimes must respond to an API probe before the gateway selects them. The VM driver is never auto-detected; configure it explicitly with compute_drivers = ["vm"] or set OPENSHELL_DRIVERS=vm in the launch environment.

Common gateway options:

Gateway TOML option	Description
`compute_drivers = ["<driver>"]`	Select the compute driver. Built-in values are `docker`, `podman`, `kubernetes`, and `vm`; custom names require `[openshell.drivers.<name>].socket_path`.

Set driver-specific values such as sandbox images, callback endpoints, network names, TLS material, and VM sizing in the gateway TOML file. See the Gateway Configuration File reference for the full [openshell.drivers.<name>] schema.

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:

1 [openshell.gateway]
2 compute_drivers = ["kyma"]
3 
4 [openshell.drivers.kyma]
5 socket_path = "/run/openshell/kyma.sock"

For a launch-time socket override, pass the same non-reserved driver name with the socket path:

$ openshell-gateway --drivers kyma --compute-driver-socket /run/openshell/kyma.sock

The gateway does not spawn, supervise, or delete extension drivers. The operator must protect the socket so only the gateway uid can access it. Reserved built-in names cannot be selected through unmanaged socket endpoints.

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.

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 callback listeners accept only supervisor callback gRPC methods. Use the gateway’s primary endpoint for CLI, administrator, health, reflection, inference-route management, and HTTP requests. A PermissionDenied response from one of the sandbox-visible callback addresses is expected for those requests. The gateway fails startup if a callback requirement resolves to the exact primary listener address because one socket cannot preserve both authorization scopes. For the IPv4-loopback callback used by Podman Machine, set bind_address = "[::1]:17670" for the primary listener and register https://localhost:17670 as the CLI endpoint. The hostname matches the generated certificate and avoids the TLS transport error produced by a raw IPv6-literal endpoint. Do not broaden the primary listener to 0.0.0.0.

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 is also required for local image builds from directories or Dockerfiles.

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

Select Docker with compute_drivers = ["docker"] in [openshell.gateway]. Configure Docker driver values such as socket_path, grpc_endpoint, network_name, supervisor_bin, supervisor_image, image_pull_policy, ssh_socket_path, sandbox_pids_limit, and guest_tls_* 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.

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

Bind mounts share gateway-host filesystem resources with the sandbox. They may be considered insecure because they can negate OpenShell controls such as workspace isolation and filesystem policy. Use them only when you understand and accept that loss of isolation.

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

1 [openshell.drivers.docker]
2 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:

Type	Fields
`bind`	`source`, `target`, optional `read_only` (`true` by default), optional `selinux_label` (`shared` for `:z` or `private` for `:Z`). `source` must be an absolute host path. Requires `enable_bind_mounts = true`.
`volume`	`source`, `target`, optional `read_only` (`true` by default), optional `subpath`. The named volume must already exist. Docker local-driver bind-backed volumes require `enable_bind_mounts = true`.
`tmpfs`	`target`, optional `options`, optional `size_bytes`, optional `mode`.

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 for a responsive Podman socket and fails to start if none respond.

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

Select Podman with compute_drivers = ["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, sandbox_ssh_socket_path, sandbox_pids_limit, and guest_tls_* in [openshell.drivers.podman].

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.

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.

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:

1 [openshell.drivers.podman]
2 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:

Type	Fields
`bind`	`source`, `target`, optional `read_only` (`true` by default), optional `selinux_label` (`shared` for `:z` or `private` for `:Z`). `source` must be an absolute host path. Requires `enable_bind_mounts = true`.
`volume`	`source`, `target`, optional `read_only` (`true` by default). The named volume must already exist. Podman local-driver bind-backed volumes require `enable_bind_mounts = true`.
`tmpfs`	`target`, optional `options`, optional `size_bytes`, optional `mode`.
`image`	`source`, `target`, optional `read_only` (`true` by default).

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 gateway restart, the gateway starts a fresh VM driver process. The driver scans its state directory for accepted sandbox launch records, restarts those VMs, and reuses each sandbox’s existing overlay.ext4 so files written inside the sandbox remain available after the supervisor reconnects.

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_drivers = ["vm"] in the gateway TOML file:

1 [openshell.gateway]
2 compute_drivers = ["vm"]

For a launch-time override, set OPENSHELL_DRIVERS=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, krun_log_level, and guest_tls_* 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.

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 falls back to the Podman socket (Docker-compatible API). 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.

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.

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

Gateway configuration	Helm value	Description
`compute_drivers = ["kubernetes"]`	Not applicable	Select the Kubernetes compute driver.
`[openshell.drivers.kubernetes].namespace`	`server.sandboxNamespace`	Set the namespace for sandbox resources. The Helm chart defaults to the release namespace when left empty.
`service_account_name`	`sandboxServiceAccount.name`	Set the Kubernetes service account assigned to sandbox pods and accepted by the gateway TokenReview bootstrap path. The Helm chart creates a dedicated sandbox service account by default.
`default_image`	`server.sandboxImage`	Set the default sandbox image.
`image_pull_policy`	`server.sandboxImagePullPolicy`	Set the Kubernetes image pull policy for sandbox pods.
`image_pull_secrets`	`server.sandboxImagePullSecrets`	Attach Kubernetes image pull secrets to sandbox pods. Referenced Secrets must exist in the sandbox namespace.
`grpc_endpoint`	`server.grpcEndpoint`	Set the gateway callback endpoint reachable from sandbox pods.
`client_tls_secret_name`	`server.tls.clientTlsSecretName`	Mount sandbox client TLS materials from a Kubernetes secret.
`supervisor_image`	`supervisor.image.repository` / `supervisor.image.tag`	Override the supervisor image that provides the `openshell-sandbox` binary. The default repository with an empty tag uses the version-pinned image built into the gateway. Changing the repository uses the effective gateway image tag, while setting a tag pins that version explicitly.
`supervisor_image_pull_policy`	`supervisor.image.pullPolicy`	Set the Kubernetes image pull policy for the supervisor image.
`supervisor_sideload_method`	`supervisor.sideloadMethod`	How the supervisor binary is delivered into sandbox pods. Leave empty to auto-detect from cluster version. Set to `image-volume` to mount the supervisor OCI image directly as a volume (requires Kubernetes 1.33+ with the ImageVolume feature gate; GA in 1.36), or `init-container` to copy it through an init container on older clusters.
`topology`	`supervisor.topology`	Set `combined` for the default single supervisor path, or `sidecar` to move pod-level network enforcement and the gateway session into a dedicated sidecar.
`sidecar.proxy_uid`	`supervisor.sidecar.proxyUid`	Non-root UID used by the relaxed sidecar when process/binary-aware network policy is disabled. The default binary-aware sidecar runs as UID 0. The network init container exempts the effective sidecar UID from proxy redirection.
`sidecar.process_binary_aware_network_policy`	`supervisor.sidecar.processBinaryAwareNetworkPolicy`	Keep process/binary-aware network policy enabled in `sidecar` topology. The default runs the sidecar as UID 0 with `SYS_PTRACE` and `DAC_READ_SEARCH`. Set false to run as `proxy_uid`, drop both capabilities, and enforce endpoint/L7 policy without matching `policy.binaries`.
`app_armor_profile`	`server.appArmorProfile`	Set the sandbox agent container’s AppArmor profile. Helm defaults this to `Unconfined` so AppArmor-enabled nodes do not block supervisor network namespace setup. Set the Helm value to an empty string to omit the field, or use `RuntimeDefault` or `Localhost/<profile-name>` for operator-managed profiles.
`workspace_default_storage_size`	`server.workspaceDefaultStorageSize`	Set the default workspace PVC size for new sandboxes.
`workspace_storage_class`	`server.workspaceStorageClass`	Set the `StorageClass` for the workspace PVC. Empty (default) omits `storageClassName` and uses the cluster’s default `StorageClass`. Set this on clusters with no default `StorageClass`, otherwise the workspace PVC stays `Pending` and the sandbox never starts.
`sa_token_ttl_secs`	`server.sandboxJwt.k8sSaTokenTtlSecs`	Set the projected ServiceAccount token TTL used for the bootstrap token exchange.

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.

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.

Sandbox.spec.volumeClaimTemplates is immutable after creation. To change storage configuration, delete the sandbox and create a new one with the updated spec.

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:

Field	Description
`volumes[].name`	Pod volume name. It must be a DNS-1123 label, unique, and not use OpenShell-managed volume names.
`volumes[].persistent_volume_claim.claim_name`	Existing PVC name in the sandbox namespace. It must be a DNS-1123 subdomain name.
`volumes[].persistent_volume_claim.read_only`	Optional. Defaults to `true`. Set `false` to allow read-write mounts.
`containers.agent.volume_mounts[].name`	References a volume declared in `volumes`.
`containers.agent.volume_mounts[].mount_path`	Absolute, normalized container path for the agent mount.
`containers.agent.volume_mounts[].sub_path`	Optional relative PVC subpath. Absolute paths and `..` are rejected.
`containers.agent.volume_mounts[].read_only`	Optional. Defaults to `true`. It cannot be `false` when the PVC volume is read-only.

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.

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 injects the sandbox UID into the rootfs guest’s /etc/passwd, /etc/group, and /etc/gshadow during rootfs preparation. Default UID is 10001; configure sandbox_uid in [openshell.drivers.vm] to use a different value.

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.