SSH Remote to HPC Error: Remote Extension host terminated unexpectedly 3 times within the last 5 minutes

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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

This failure “Remote Extension host terminated unexpectedly 3 times within the last 5 minutes.” occurs immediately after the cursorsandbox preflight check fails due to restricted kernel permissions. On HPC cluster (like TACC I’m using), max_user_namespaces is set to 0, causing the sandbox to trigger a misleading ENOSPC (resource exhaustion) error.

It appears that the failure of the sandbox preflight check causes the Extension Host to hang or crash, preventing any AI “agent” or “provider” from executing commands. The connection to the HPC will be disconnected a few minutes after I receive this failure notification.

Error Logs

  1. Extension Host / AI Timeout:
The agent execution provider did not respond within 16 seconds. 
This may indicate the extension host is not running or is unresponsive.
  1. Underlying Sandbox Failure:
[error] [shell-exec:sandbox] [isSandboxHelperSupported] Preflight failed: 
Command failed: <REMOTE_DIR>/.cursor-server/bin/linux-x64/.../cursorsandbox
Error: Failed to apply sandbox: IO error: Step 1-2/7 (user namespace) failed: 
Failed to unshare namespaces: ENOSPC: No space left on device

Attempted Workarounds (Failed)

  • Disabling terminal.integrated.sandbox and shellintegration in both User and Remote settings.json.

  • Changing AI Agent auto-run to “Run Everything”.

The preflight check continues to run and crash the host regardless of these settings.

Steps to Reproduce

Local OS: macOS

Remote OS: Linux (Restricted HPC Environment)

Remote Kernel Config: /proc/sys/user/max_user_namespaces = 0

Disk Status: High availability (>10GB free), but triggering ENOSPC on unshare.

Operating System

Linux

Version Information

Version: 2.4.31
VSCode Version: 1.105.1
Commit: 3578107fdf149b00059ddad37048220e41681000
Date: 2026-02-08T07:42:24.999Z
Build Type: Stable
Release Track: Default
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin arm64 25.2.0

Additional Information

How can we force-disable the sandbox preflight check to allow the Extension Host to stay alive on systems where user namespaces are prohibited? Currently, this is a total blocker for using Cursor AI features on high-security research clusters.

Does this stop you from using Cursor

Sometimes - I can sometimes use Cursor

4

Hey, thanks for the report. This is a known issue. The sandbox preflight check crashes the Extension Host instead of degrading gracefully when user namespaces are disabled.

If you have sudo on the HPC, try one of these:

sudo sysctl -w kernel.unprivileged_userns_clone=1

Or set setuid on the sandbox binary:

sudo chown root: ~/.cursor-server/bin/linux-x64/.../cursorsandbox
sudo chmod 4755 ~/.cursor-server/bin/linux-x64/.../cursorsandbox

More details in this thread: "Activating Extensions" message, extensions don't work -- solution

If you don’t have sudo access, there’s no user-side workaround right now. I’ve passed this to the team, and your report helps raise the priority.

7

Hey there!

This should be fixed as of the latest versions of 2.5.