Adjust the process ulimit to the maximum allowed on startup #17464
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zanieb
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Jan 14, 2026
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Linux defaults to a low open file limit (1024) and macOS also defaults to a low soft limit (256). On modern multi-core machines, uv may schedule more concurrent work than these limits allow, causing "too many open files" errors. This adds a new `uv-unix` crate that raises the soft limit to the hard limit at startup. The raised limit is inherited by child processes spawned via `uv run`. See: astral-sh#16999
The ulimit adjustment is now gated behind the `adjust-ulimit` preview feature, which can be enabled via `--preview` or `--preview-features=adjust-ulimit`.
This matches the typical Linux default (`/proc/sys/fs/nr_open`) and avoids issues with extremely high limits that can break code expecting i32 values or cause timeouts when iterating over all possible FDs. OpenJDK uses the same cap for similar reasons. See: https://bugs.openjdk.org/browse/JDK-8324577 See: oracle/graal#11136
Use `rlim_t` instead of `u64` for the `MAX_NOFILE_LIMIT` constant since `rlim_t` is platform-specific (`u64` on Linux/macOS, `i64` on FreeBSD). Add a `rlim_t_to_u64` helper for safe conversion that returns `None` for negative values (defensive, since resource limits should never be negative in practice). Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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konstin
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| /// We cap at 0x100000 (1,048,576) to match the typical Linux default (`/proc/sys/fs/nr_open`) | ||
| /// and to avoid issues with extremely high limits. | ||
| /// | ||
| /// `OpenJDK` uses this same cap because: | ||
| /// | ||
| /// 1. Some code breaks if `RLIMIT_NOFILE` exceeds `i32::MAX` (despite the type being `u64`) | ||
| /// 2. Code that iterates over all possible FDs, e.g., to close them, can timeout | ||
| /// | ||
| /// See: <https://bugs.openjdk.org/browse/JDK-8324577> | ||
| /// See: <https://github.com/oracle/graal/issues/11136> | ||
| /// | ||
| /// Note: `rlim_t` is platform-specific (`u64` on Linux/macOS, `i64` on FreeBSD). |
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tmeijn
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This MR contains the following updates: | Package | Update | Change | |---|---|---| | [astral-sh/uv](https://github.com/astral-sh/uv) | patch | `0.9.24` → `0.9.26` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>astral-sh/uv (astral-sh/uv)</summary> ### [`v0.9.26`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0926) [Compare Source](astral-sh/uv@0.9.25...0.9.26) Released on 2026-01-15. ##### Python - Add CPython 3.15.0a5 ##### Enhancements - Add a hint to update uv when a managed Python download is not found ([#​17461](astral-sh/uv#17461)) - Improve cache initialization failure error message ([#​17469](astral-sh/uv#17469)) - Improve error message for abi3 wheels on free-threaded Python ([#​17442](astral-sh/uv#17442)) - Add support for `--no-sources-package` ([#​14910](astral-sh/uv#14910)) ##### Preview features - Add `METADATA.json` and `WHEEL.json` in uv build backend ([#​15510](astral-sh/uv#15510)) - Add support for GCS request signing ([#​17474](astral-sh/uv#17474)) - Adjust the process ulimit to the maximum allowed on startup ([#​17464](astral-sh/uv#17464)) ##### Bug fixes - Lock to avoid concurrent refresh of pyx tokens ([#​17479](astral-sh/uv#17479)) ##### Documentation - Add linting and formatting instructions to the CONTRIBUTING guide ([#​17470](astral-sh/uv#17470)) - Avoid rendering `pyproject.toml` examples for more system-level settings ([#​17462](astral-sh/uv#17462)) ### [`v0.9.25`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0925) [Compare Source](astral-sh/uv@0.9.24...0.9.25) Released on 2026-01-13. ##### Python - Add CPython 3.15.0a4 - Upgrade Tcl/Tk used by CPython to 9.0 ##### Enhancements - Add `--compile-bytecode` to `uv python install` and `uv python upgrade` to compile the standard library ([#​17088](astral-sh/uv#17088)) - Allow disabling `exclude-newer` per package ([#​16854](astral-sh/uv#16854)) - Broadcast `WM_SETTINGCHANGE` on `uv tool update-shell` ([#​17404](astral-sh/uv#17404)) ##### Preview features - Detect workspace from `uv run` target ([#​17423](astral-sh/uv#17423)) ##### Bug fixes - Avoid unwrapping size for file responses ([#​17434](astral-sh/uv#17434)) - Use keyring authentication when retrieving `tool@latest` version ([#​17448](astral-sh/uv#17448)) - Use latest Pyodide version for each python version ([#​17372](astral-sh/uv#17372)) - Improve trampoline file handle closing ([#​17374](astral-sh/uv#17374)) - Fix error message when installing musl python on armv7 ([#​17213](astral-sh/uv#17213)) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this MR, check this box --- This MR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0Mi44MC4xIiwidXBkYXRlZEluVmVyIjoiNDIuODEuOCIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOlsiUmVub3ZhdGUgQm90IiwiYXV0b21hdGlvbjpib3QtYXV0aG9yZWQiLCJkZXBlbmRlbmN5LXR5cGU6OnBhdGNoIl19-->
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Closes #16999
See the commentary at #16999 (comment) for precedence in other tools.
This is non-fatal on error, but there are various scary behaviors from increased ulimit sizes so I've gated this with preview.