rustup-init fails when invoked in parallel

[konstin]

Verification

• I searched for recent similar issues at https://github.com/rust-lang/rustup/issues?q=is%3Aissue and found no duplicates.
• I am on the latest version of Rustup according to https://github.com/rust-lang/rustup/tags and am still able to reproduce my issue.

Problem

When rustup-init -y runs in parallel, multiple processes write the same partial file, and then try to move it to the same target location. One of those process succeeds and renames the file, the other processes error due to the missing file:

error: component download failed for cargo-x86_64-unknown-linux-gnu: could not rename 'downloaded' file from '/home/konsti/projects/rustup/rustup/downloads/8d17d5a4734e684228adee4ea4a75da94eb7f71993804adf29f344709e65fe09.partial' to '/home/konsti/projects/rustup/rustup/downloads/8d17d5a4734e684228adee4ea4a75da94eb7f71993804adf29f344709e65fe09': No such file or directory (os e

After locking those files, the transaction step fails when running in parallel:

error: failed to install component: 'cargo-x86_64-unknown-linux-gnu', detected conflict: 'bin/cargo'

Steps

MRE:

rm -rf $PWD/cargo $PWD/rustup
CARGO_HOME=$PWD/cargo/ RUSTUP_HOME=$PWD/rustup target/debug/rustup-init -y --no-modify-path --profile minimal & \
  CARGO_HOME=$PWD/cargo/ RUSTUP_HOME=$PWD/rustup target/debug/rustup-init -y --no-modify-path --profile minimal & \
  CARGO_HOME=$PWD/cargo/ RUSTUP_HOME=$PWD/rustup target/debug/rustup-init -y --no-modify-path --profile minimal
wait -n

Possible Solution(s)

There's two popular options:

• Use a unique (temporary) file or directory instead of just .partial
• Use file locks

Prototype: #4606

A temp file has wider support (no requirement on OS level locking), file locks actually prevent multiple processes downloading the same, and may be required for fixing parallel transactions. For the unique file name solution, I wouldn't know how to implement cleaning up previous failures, while there's an existing implementation when using locking.

Notes

No response

Rustup version

rustup-init 1.28.2+424 (4ae201236 2025-11-19)

Installed toolchains

n/a

OS version

Ubuntu 24.04

[rami3l]

@konstin Thanks for noticing this bug.

In fact it's a very well-known and long-standing issue (#988 posted by no other than the legendary matklad) that is on my radar and I expect to start working on it in the upcoming months. Please stay tuned!

Would you mind if I close this issue as a duplicate?

---

PS: I of course understand that locking the file being downloaded (#4606) is not a complete solution (it might not be platform-neutral even), but I'll have to evaluate whether that fits into the big picture of things. Thanks nonetheless for the PR!

[konstin]

I was looking for "parallel" instead of "concurrent", otherwise I would have commented there!