Go "too many open files" (ulimit) - Fix in CI

By Daniel Zoghalchali·Latchkey

Large builds and parallel tests open many files and sockets at once. When the open-file ulimit is low, the toolchain hits the cap and fails with "too many open files".

What this error means

A build or test fails with too many open files opening a package file or socket. The runner file-descriptor limit was exceeded under parallelism.

open /home/runner/go/pkg/mod/example.com/lib@v1.2.0/file.go: too many open files

Common causes

Low file-descriptor ulimit

The default soft limit is too low for a large parallel build or test run.

Excessive build parallelism

High -p fans out many compile actions, each holding open files, exhausting the limit.

How to fix it

Raise the open-file limit

1. Increase the soft ulimit before building.

- run: |
    ulimit -n 8192
    go build ./...

Reduce parallelism

1. Lower -p so fewer files are open at once.

go test -p 2 ./...

How to prevent it

• Raise ulimit -n in CI for large builds.
• Cap -p when descriptor pressure is high.
• Close files and connections promptly in tests.

Frequently asked questions

Related guides

References

• Go documentation
• GitHub Actions documentation