CLAUDE_CODE_TMPDIR

mkdir -p /tmp/custom-claude-tmp

CLAUDE_CODE_TMPDIR is an environment variable that overrides the default temp directory where Claude Code stores internal session files, scratchpad, and transient artifacts.

How It Works

Setting CLAUDE_CODE_TMPDIR=/path/to/dir before invoking claude redirects all session-local temp storage to that directory. Claude Code replicates its standard directory hierarchy inside the custom root: {CLAUDE_CODE_TMPDIR}/claude/{project-path}/{session-id}/scratchpad/ and related structures. The project path encodes forward slashes as dashes for filesystem compatibility.

What the Test Found

Runtime testing (2026-01-16, version 2.1.5 on 2.1.9) confirmed the feature works as specified. A custom temp directory was set via environment variable, and Claude Code created its full internal structure at that location without errors. The scratchpad and session isolation remained intact. The layout mirrored the default behavior exactly, confirming no special logic is required at the application level—the override is transparently wired into the runtime's temp-file machinery.

Use Cases and Implications

Five classes of deployments benefit: ramdisk/tmpfs environments requiring fast temp I/O; Docker volumes persisting temp files across container restarts; cluster/NFS filesystems with custom mount points; debugging workflows isolating session artifacts for inspection; quota constraints or security isolation directing temp writes to separate partitions or secured locations.

Caveats

The override is orthogonal to other runtime features (scratchpad functionality, background task disabling, large output persistence). The variable applies session-wide and requires correct path permissions; Claude Code will not create parent directories. If unset, the runtime defaults to the platform's conventional temp location.

Evidence & receipt

file2.1.5/tests/01-tmpdir-env-var/TEST-RESULTS.md

◇ ed25519 receipt

idprimitive_6cdaf19393e90d4a5535636a

alged25519

pubkey9b87705613b1e2fd064d57fa75a6b679d2856ceafad6b1daa8f982493871b6dd

sig

aaed35c826362afd1c8f516cc306524c2b718a2ff5676049b770bf10ffec668bfb30adc177769594339d3601a7b304a818b4762cfc709fb216991c39c83bd70e

Signed with an ed25519 key held off the repo. Anyone can verify against the published public key; nobody without the secret key can forge it. Click verify: it recomputes the signature in your browser. The signature proves integrity and authorship of this exact content — not a third-party timestamp or that the underlying claim is objectively true. signedAt is when the @f3/attest pipeline ran, not when the work happened; the evidence refs carry the source dates.

Connected

instance-of Skill Runtime Class
introduces (in) 2.1.5 Test (2.1.5) Release
verifies (in) CLAUDE_CODE_TMPDIR — runtime test Test

CLAUDE_CODE_TMPDIR

Primitive

Kind	Primitive
Introduced	Claude Code 2.1.5
Class	Skill Runtime
Epistemic	tested · runtime-test
Evidence	1 ref
Receipt	ed25519 · verifiable

Hands-on runtime test · Claude Code 2.1.5

Cite this page

Hunter, R. "CLAUDE_CODE_TMPDIR." The Runtime Atlas. Content-addressed entity primitive_6cdaf19393e90d4a5535636a, ed25519-signed (integrity, not third-party timestamp). https://ryanhunter.io/atlas/e/2-1-5-tmpdir-env-var

@misc{atlas-2-1-5-tmpdir-env-var,
  title  = {CLAUDE_CODE_TMPDIR},
  author = {Hunter, Ryan},
  note   = {The Runtime Atlas; entity primitive_6cdaf19393e90d4a5535636a; ed25519-signed for integrity},
  url    = {https://ryanhunter.io/atlas/e/2-1-5-tmpdir-env-var}
}