OVPhysX Remove Start Script — Design Spec

Issue: #5323 — [OVPHYSX] Remove start script
Date: 2026-04-20
Status: Draft

Summary

Remove or replace the scripts/run_ovphysx.sh start script. Currently, OVPhysX requires a separate shell script to launch because it needs to override LD_PRELOAD to load its bundled PhysX libraries instead of Kit's. The goal is to make OVPhysX usable through the standard ./isaaclab.sh -p launcher.

Current Problem

From PR #4852 review:

• run_ovphysx.sh unconditionally overwrites LD_PRELOAD rather than prepending, silently discarding any existing preloaded libraries
• The script cannot coexist with Kit (it overrides Kit's library paths)
• Users must remember to use a different launch script for OVPhysX vs PhysX

Desired State

OVPhysX should be launchable via the standard ./isaaclab.sh -p command, with the physics backend selected by configuration (e.g., physics_cfg=OvPhysxCfg()), not by which shell script you run.

Approach Options

Option A: Integrate LD_PRELOAD into OvPhysxManager initialization

Instead of a shell wrapper, have OvPhysxManager.initialize() programmatically adjust library loading:

• Use ctypes.CDLL to preload the required ovphysx shared libraries at Python runtime
• Or use os.environ["LD_PRELOAD"] early in the import chain (before any conflicting libraries are loaded)

Risk: LD_PRELOAD must be set before the process starts for it to affect library resolution. Setting it after process start may not work for all libraries.

Option B: Use a Python entry point that re-execs with correct LD_PRELOAD

OvPhysxCfg detection in the launcher causes a os.execve re-launch with the correct LD_PRELOAD:

• First invocation detects OVPhysX config, sets LD_PRELOAD, re-execs
• Second invocation runs normally with correct libraries

Risk: Adds complexity to the launcher. Double-start may confuse debuggers.

Option C: Namespace-isolate ovphysx's Carbonite (ovphysx-side fix)

Have ovphysx bundle its libraries with a different soname so they don't conflict with Kit's:

• No LD_PRELOAD needed at all
• Both Kit and ovphysx can coexist in the same process

This is the ideal long-term solution but requires work from @marcodiiga on the ovphysx packaging side.

Recommendation

Short term: Option B (re-exec with correct LD_PRELOAD via launcher detection). This is pragmatic and works now.

Long term: Option C (namespace-isolated Carbonite in ovphysx). This eliminates the problem entirely.

Blocker for @marcodiiga: The dual-Carbonite conflict (os._exit(0) workaround in OvPhysxManager) and the LD_PRELOAD requirement are both symptoms of the same root cause — ovphysx and Kit share the same Carbonite library. Namespace isolation on the ovphysx side would fix both issues.

Implementation Steps

1. Move LD_PRELOAD logic from run_ovphysx.sh into isaaclab.sh or the Python launcher
2. Detect OVPhysX backend selection early in the startup path
3. If OVPhysX is selected and LD_PRELOAD is not set, re-exec with correct value
4. Remove run_ovphysx.sh after migration

Dependencies

• Requires PR ovphysx backend integration #4852 merged
• Option C requires ovphysx packaging changes
• Independent of asset/sensor specs

Estimated Scope

• Launcher integration: ~50 lines in isaaclab.sh or sim_launcher.py
• Testing: manual verification of launch flow
• Script removal: delete scripts/run_ovphysx.sh