# std.Build.tmpPath() directory not cleaned up

**URL:** <https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888>\
**Category:** Help\
**Tags:** build-system\
**Created:** [October 8, 2026, 5:47am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888 "2026-10-08T05:47:35Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![Zemogus](https://ziggit.dev/user_avatar/ziggit.dev/zemogus/32/1421_2.png) [@Zemogus](https://ziggit.dev/u/Zemogus)\
**Post date:** [October 8, 2026, 5:47am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/1 "2026-10-08T05:47:35Z")

</div>

I’m trying to pass a temporary directory to a test. However the temporary subdir created by the build system doesn’t seem to get deleted? Am I doing something wrong?

Minimal reproducible example:

Zig 0.17.0

> **build.zig**
>
> ```zig
> const std = @import("std");
> 
> pub fn build(b: *std.Build) void {
> const exe = b.addExecutable(.{
> .name = "main",
> .root_module = b.createModule(.{
> .root_source_file = b.path("main.zig"),
> .target = b.standardTargetOptions(.{}),
> .optimize = b.standardOptimizeOption(.{}),
> }),
> });
> 
> const options = b.addOptions();
> options.addOptionPathDirectory("tmp_dir", b.tmpPath());
> exe.root_module.addImport("options", options.createModule());
> 
> const run_exe = b.addRunArtifact(exe);
> b.default_step.dependOn(&run_exe.step);
> }
> 
> ```

> **main.zig**
>
> ```zig
> const std = @import("std");
> const options = @import("options");
> 
> pub fn main(init: std.process.Init) !void {
> _ = try std.Io.Dir.createFile(
> .cwd(),
> init.io,
> options.tmp_dir ++ "/delete-me",
> .{},
> );
> }
> 
> ```

Run

```sh
> zig build
> find .zig-cache/tmp
.zig-cache/tmp
.zig-cache/tmp/9451b85aaf0d789b
.zig-cache/tmp/9451b85aaf0d789b/delete-me

```

---

<div class="post-metadata">

**Author:** ![pzittlau](https://ziggit.dev/letter_avatar_proxy/v4/letter/p/ecae2f/32.png) [@pzittlau](https://ziggit.dev/u/pzittlau)\
**Post date:** [October 8, 2026, 7:47am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/2 "2026-10-08T07:47:53Z")

</div>

This may be wrong so take it with a grain of salt. But as far as I understand it the `tmp_dir` in the `build.zig` is just for building the code and _not_ running it. Meaning that it may or may not later be deleted when you run the tests.

* * *

You can have a temporary directory for tests like this:

```zig
test "tmp_dir" {
    var tmp = std.testing.tmpDir(.{});
    defer tmp.cleanup();

    // ... Your code
}

```

Here is the entire code:

> **build.zig**
>
> ```zig
> const std = @import("std");
> 
> pub fn build(b: *std.Build) void {
> const exe = b.addExecutable(.{
> .name = "main",
> .root_module = b.createModule(.{
> .root_source_file = b.path("main.zig"),
> .target = b.standardTargetOptions(.{}),
> .optimize = b.standardOptimizeOption(.{}),
> }),
> });
> 
> const exe_tests = b.addTest(.{ .root_module = exe.root_module });
> const run_exe_tests = b.addRunArtifact(exe_tests);
> 
> const test_step = b.step("test", "Run tests");
> test_step.dependOn(&run_exe_tests.step);
> }
> 
> ```

> **main.zig**
>
> ```zig
> const std = @import("std");
> const testing = std.testing;
> 
> test "tmp_dir" {
> const io = testing.io;
> 
> var tmp = testing.tmpDir(.{});
> defer tmp.cleanup();
> 
> _ = try tmp.dir.createFile(io, "delete-me", .{});
> 
> // ... Your code
> }
> 
> ```

Then just run `zig build test`.

---

<div class="post-metadata">

**Author:** ![Zemogus](https://ziggit.dev/user_avatar/ziggit.dev/zemogus/32/1421_2.png) [@Zemogus](https://ziggit.dev/u/Zemogus)\
**Post date:** [October 8, 2026, 8:08am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/3 "2026-10-08T08:08:17Z")

</div>

I was not aware of `std.testing.tmpDir`. That sounds more like what I want and now the folder gets cleaned up!

---

<div class="post-metadata">

**Author:** ![matklad](https://ziggit.dev/user_avatar/ziggit.dev/matklad/32/2462_2.png) [@matklad](https://ziggit.dev/u/matklad)\
**Post date:** [October 8, 2026, 10:13am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/4 "2026-10-08T10:13:18Z")

</div>

Actually, I think @Zemogus what you originally wanted is fundamentally a better approach.

The problem with `std.testing.tmpDir(.{})` and any equivalents is that the clean up is cooperative — it’s the testing process that deletes it, before it exits. That is problematic, because the code we are testing often crashes (or hangs, and is then killed by the test-running infrastructure), so no defers are run, and the are leftovers on the file system, which could eventually occupy all of the disk space (don’t ask 😃 )

It’s more reliable to make the _parent_ process create and dispose of a temporary directory. In some sense, it is just kicking the can down the road (what if the parent dies abruptly), but in practical sense it isn’t: the parent code (`build.zig`) is stable, it rarely changes and is assumed to be bug free. But the code under test is buggy, that’s why we are testing it in the first place!

Alas, I don’t think you can achieve this in “userspace” in build.zig:

- As far as I am aware, you can’t create a temporary directory before the step runs, and then clean it up later.
- You’d want to pass that directory as a _runtime_ argument to the tests, rather than a comptime-one, but this isn’t possible.

I think I do with that build.zig had this sort of facility, but, practically, just use `std.testing.tmpDir` and maybe drop `.zig-cache/tmp` once in a while manually.

---

<div class="post-metadata">

**Author:** ![Zemogus](https://ziggit.dev/user_avatar/ziggit.dev/zemogus/32/1421_2.png) [@Zemogus](https://ziggit.dev/u/Zemogus)\
**Post date:** [October 8, 2026, 10:45am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/5 "2026-10-08T10:45:18Z")

</div>

I must consider myself quite lucky then. Because what my test does is essentially:

- write some files
- spawn the process to be tested
- check stdout and stderr

So it’s unlikely that the test code ever crashes.

---

<div class="post-metadata">

**Author:** ![pzittlau](https://ziggit.dev/letter_avatar_proxy/v4/letter/p/ecae2f/32.png) [@pzittlau](https://ziggit.dev/u/pzittlau)\
**Post date:** [October 8, 2026, 12:39pm UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/6 "2026-10-08T12:39:04Z")

</div>

> [@matklad](#):
>
> - As far as I am aware, you can’t create a temporary directory before the step runs, and then clean it up later

I’m also not aware something like this exists. But one could just have a stable `tmp_dir` across runs and let the next run clean it up if it already exists. But this is then inherently racy, which could lead to other problems.

> [@matklad](#):
>
> - You’d want to pass that directory as a _runtime_ argument to the tests, rather than a comptime-one, but this isn’t possible.

One _could_ pass it via some sidechannel like a file but this also bad because of various obvious reasons.

---

<div class="post-metadata">

**Author:** ![alanza](https://ziggit.dev/user_avatar/ziggit.dev/alanza/32/6006_2.png) [@alanza](https://ziggit.dev/u/alanza)\
**Post date:** [October 9, 2026, 1:28am UTC](https://ziggit.dev/t/std-build-tmppath-directory-not-cleaned-up/17888/7 "2026-10-09T01:28:36Z")

</div>

Have we forgotten that Zig lets you write your own test runner?