CLAUDE_CODE_TMPDIR — runtime test
Hands-on runtime battle-test of CLAUDE_CODE_TMPDIR. Result: PASS.
CLAUDE_CODE_TMPDIR is an environment variable that overrides the default temporary directory where Claude Code stores session-local files like scratchpads and large output artifacts.
How It Works
Claude Code normally stores temp files in the system's default /tmp directory under a hierarchical structure: claude/{project-path}/{session-id}/scratchpad/. Setting CLAUDE_CODE_TMPDIR=/path/to/custom/dir redirects this entire subtree to the custom location while preserving the internal directory layout.
The variable accepts an absolute path and requires no additional configuration. When set, Claude creates its standard claude/ prefix subdirectory within the custom location, followed by the same project-path-based nesting and session segregation.
What the Test Found
Runtime test on 2026-01-16 (version 2.1.5 features on 2.1.9 runtime) verified the mechanism by setting CLAUDE_CODE_TMPDIR=/tmp/custom-claude-tmp and running a simple Claude Code invocation. Result: PASS.
The custom directory received the complete standard structure:
/tmp/custom-claude-tmp/
└── claude/
└── -Users-ryanhunter-projects-claude-claude-feature-demos/
└── {session-id}/
└── scratchpad/
Scratchpad and large output persistence both integrate cleanly with the custom tmpdir. No failures or data loss observed across session restarts.
Why It Matters
This enables targeted temp storage for performance, compliance, and operational constraints. Common applications: ramdisk/tmpfs mounting for latency-critical sessions; Docker volume persistence across container restarts; NFS or cluster shared-filesystem placement; quota-constrained environments where /tmp lacks capacity; and security isolation of temporary artifacts in regulated systems.
Caveats
The feature is orthogonal to other Claude Code configuration—it does not interact with session disabling or background task controls. Custom directory must exist and be writable before invocation; Claude does not create the parent path. Permissions follow standard POSIX rules.
Test Results: CLAUDE_CODE_TMPDIR
Feature: Added CLAUDE_CODE_TMPDIR environment variable to override the temp directory used for internal temp files
Tested: 2026-01-16 Version: 2.1.5 features on 2.1.9
Test
mkdir -p /tmp/custom-claude-tmp
CLAUDE_CODE_TMPDIR=/tmp/custom-claude-tmp claude -p "say hi"
ls -laR /tmp/custom-claude-tmp/
Result: PASS
Claude created its standard temp structure in the custom directory:
/tmp/custom-claude-tmp/
└── claude/
└── -Users-ryanhunter-projects-claude-claude-feature-demos/
└── {session-id}/
└── scratchpad/
The structure mirrors the default temp directory layout:
claude/prefix- Project path (with slashes replaced)
- Session UUID
- scratchpad subdirectory
Use Cases
- Ramdisk/tmpfs - Point to fast storage for performance
- Docker volumes - Persist temp files across container restarts
- Shared filesystem - Custom temp location in NFS/cluster environments
- Debugging - Isolate temp files for inspection
- Quota constraints - Use different partition if /tmp has quota
- Security - Isolate temp files in specific location
Interaction with Other Features
- Works with scratchpad (scratchpad created inside custom tmpdir)
- Works with large output persistence (would write to custom location)
- Compatible with DISABLE_BACKGROUND_TASKS (orthogonal)
Notes
Simple, focused env var. Does exactly what it says.
Status: PASS
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- verifies CLAUDE_CODE_TMPDIR Primitive