[BUG] /tmp/claude path collision on shared HPC/multi-user systems

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code hardcodes /tmp/claude/ for task management and background processes. On shared multi-user systems (HPC clusters, shared servers), the first user to run Claude creates this directory with default permissions (755). All subsequent users receive permission denied errors:

Error: EACCES: permission denied, mkdir '/tmp/claude/-global-home-users-username--claude/tasks'

This affects:

• The Task tool (agent subprocesses)
• Background tasks (run_in_background)
• Plugin installation
• Any operation that spawns child processes

Core functionality (Read, Write, Edit, Grep, Glob) still works, but agent-based workflows are broken.

What Should Happen?

Expected Behavior

Claude Code should either:

1. Respect the TMPDIR environment variable for all temp directory operations
2. Provide a configuration option (e.g., CLAUDE_TMPDIR or setting in settings.json)
3. Use a user-specific temp path like /tmp/claude-$USER/ or $HOME/.claude/tmp/

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce

1. User A runs Claude Code on a shared system → /tmp/claude created with permissions drwxr-xr-x owned by User A
2. User B runs Claude Code on the same system → EACCES error because User B cannot write to /tmp/claude

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.2

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

PowerShell

Additional Information

Workarounds Attempted

• Setting TMPDIR environment variable → No effect, Claude ignores it
• Adding env vars to settings.local.json → No effect
• Manual directory creation → Cannot create inside /tmp/claude without permissions

Current Workaround

Contact system administrators to remove /tmp/claude so it can be recreated, but this is not sustainable on shared systems.

Additional Context

This is a common issue on:

• University HPC clusters
• Shared development servers
• Container environments with shared /tmp
• Any multi-tenant Linux system

Related issues: #14242, #10194, #11079