Fixing Claude Code EACCES: Multi-User Linux Permission Architecture

When you're running Claude Code across multiple Linux user accounts and hit EACCES: permission denied, the solution isn't just chmod 777. This is the complete troubleshooting journey from error to production-ready multi-user architecture. The Problem: Two Users, One Claude Code Instance Initial symptom: User jeremy couldn't start Claude Code: EACCES: permission denied, open syscall: "open", errno: -13, code: "EACCES" Context: Two user accounts: jeremy (master) and admincostplus (admin) Both need to run Claude Code independently Shared configuration desired (plugins, MCP servers, slash commands) No permission conflicts or ownership battles The naive approach? "Just give both users access." The correct approach? Architect a system that scales. Phase 1: Understanding the Problem (What We Discovered) Investigation Started with Basic Checks # Check current user and home whoami # admincostplus ls -la ~/.claude # Owned by admincostplus, 700 permissions # Try to identify what's failing claude