Move default output root on macOS to `$HOME/Library/Caches` #25262

aaronsky · 2025-02-12T10:10:20Z

Implements the request made here and moves the default output root on macOS from /private/var/tmp to $HOME/Library/Caches. May constitute an incompatible change, though on a cursory glance I didn't see any precedent for incompatible startup options in source.

src/main/cpp/blaze_util_darwin.cc

src/test/cpp/bazel_startup_options_test.cc

tetromino · 2025-02-18T17:58:47Z

This is an incompatible change, but arguably one that doesn't need to be gated by a flag. We do need to make sure that

the change is described in bazel 9 release notes
it doesn't get cherry-picked into 8.x point releases

An additional question is what to do about the documentation at https://bazel.build/remote/output-directories - I assume many bazel 8 users will check that page (even though it's for bazel-at-head). So maybe we need phrasing along the lines of "this is how things work in bazel 9, and that is how they used to work in bazel 8 and earlier".

tetromino · 2025-02-18T19:28:16Z

Did some code searching.

Needs to be fixed:

Google has a bunch of CI and admin scripts internally with /private/var/tmp hard-coded. We need to migrate them before or soon after merging this PR. (Internal tracking bug 397461058).
Fix https://github.com/bazelbuild/continuous-integration/blob/master/macos/mac-cleanup.sh
Fix Bazel example config at https://github.com/actions/cache/blob/main/examples.md because it looks like many people are copy-pasting it

Already fixed:

DarwinSandboxedSpawnRunner.java already marks ~/Library/Caches as always-writable

tetromino

Please also update output-directories.md.

I'd suggest something like the following wording:

The outputRoot directory defaults to ~/.cache/bazel on Linux,
~/Library/Caches/bazel on macOS (when using Bazel 9 and newer), and on Windows it defaults to %HOME% if
set, else %USERPROFILE% if set, else the result of calling
SHGetKnownFolderPath() with the FOLDERID_Profile flag set. If the
environment variable $XDG_CACHE_HOME is set on either Linux or
macOS, the value ${XDG_CACHE_HOME}/bazel will override the default.
If the environment variable $TEST_TMPDIR is set, as in a test of Bazel
itself, then that value overrides any defaults.
- Note that Bazel 8.x and earlier on macOS used /private/var/tmp as outputRoot, and ignored $XDG_CACHE_HOME.

src/main/cpp/blaze_util_darwin.cc

aaronsky · 2025-02-18T23:43:25Z

Thanks for the feedback @tetromino! I've addressed it in the latest commit. I'm happy to continue working with you to iterate on this as needed. I don't know if I'm the best person to work on those other identified points, since some of them are internal to Google and others seem to require some inter-repo coordination, but let me know what you want from me!

meteorcloudy · 2025-03-04T15:48:53Z

@tetromino Can you take another look?

aaronsky · 2025-03-19T00:39:09Z

@tetromino would you mind taking another look at this?

aaronsky · 2025-04-18T12:23:10Z

@tetromino bumping this. would you mind taking another look at this PR?

tetromino · 2025-05-02T21:28:04Z

I got feedback from Bazel users at Google asking to move the default output root to /tmp (a.k.a. /private/tmp) instead. On macOS, /tmp gets wiped on reboot by default, which keeps keeps the amount of disk space used by Bazel in check.

Apparently, running out of disk space due to Bazel is a problem that many engineers experienced - one user reported >200 GB in their output root at one point.

In light of this, I'd like to defer this PR review and first discuss what we want to do with the output root in #25260

tetromino · 2025-11-08T01:41:23Z

Quoting @ashgti from internal bug report:

Some notes on folders macOS uses:

Path	Permissions	Cleanup
/tmp	+777	reboot
/var/tmp	+777	never
/Library/Caches	+777	never
~/Library/Caches	+700	never
getconf DARWIN_USER_CACHE_DIR ¹ (like `/var/folders/_0/_vrx1th904x4bsf1c0_w4bhw00g80m/C/`)	+700	reboot
$TEMPDIR (getconf DARWIN_USER_TEMP_DIR) ¹ (like `/var/folders/_0/_vrx1th904x4bsf1c0_w4bhw00g80m/T/`)	+700	reboot and periodic mtime >3 days

End of quote.

Since /var/tmp and ~/Library/Caches have the same cleanup behavior, the only problem with moving from one to the other is needing to adjust various scripts for CI etc.

The fix for @nglevin's issue might be to launch bazel with --user_cache_dir=$(getconf DARWIN_USER_TEMP_DIR) in google's internal launcher script - but we need to investigate whether there's a risk of the dirhelper demon deleting bazel's cache files while bazel is running.

See man confstr on macOS or https://github.com/apple-oss-distributions/Libc/blob/af11da5ca9d527ea2f48bb7efbd0f0f2a4ea4812/gen/confstr.3 ↩ ↩²

tetromino

After thinking about this for a while, I think it's ok.

If we get complaints, we'll roll it back.

The solution for the running-out-of-space problem might be to set --user_cache_dir=$(getconf DARWIN_USER_TEMP_DIR) in the script that launches Bazel.

Fixes bazelbuild#25260 Implements the request made [here](bazelbuild#25205 (comment)) and moves the default output root on macOS from `/private/var/tmp` to `$HOME/Library/Caches`. May constitute an incompatible change, though on a cursory glance I didn't see any precedent for incompatible startup options in source. Closes bazelbuild#25262. PiperOrigin-RevId: 840604399 Change-Id: I391b805b2c8e99d3ffe44a76e916d1c9839225e5

…27875) Fixes #25260 Implements the request made [here](#25205 (comment)) and moves the default output root on macOS from `/private/var/tmp` to `$HOME/Library/Caches`. May constitute an incompatible change, though on a cursory glance I didn't see any precedent for incompatible startup options in source. Closes #25262. PiperOrigin-RevId: 840604399 Change-Id: I391b805b2c8e99d3ffe44a76e916d1c9839225e5 Commit 13da9a1 Co-authored-by: Aaron Sky <[email protected]>

Move default output root on macOS to $HOME/Library/Caches

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[9.0.0] Move default output root on macOS to $HOME/Library/Caches #27875

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Move default output root on macOS to $HOME/Library/Caches #25262

Move default output root on macOS to $HOME/Library/Caches #25262

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Move default output root on macOS to `$HOME/Library/Caches` #25262

Move default output root on macOS to `$HOME/Library/Caches` #25262

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