Node.js "EMFILE: too many open files" in CI

A process exceeded the per-process file-descriptor limit. Tools that open many files at once (bundlers, test runners, watchers) hit EMFILE on runners with a low ulimit.

What this error means

A build or test run fails with EMFILE: too many open files. It can be intermittent depending on concurrency, and often points at a glob or a parallel file-reading step.

node

Error: EMFILE: too many open files, open
'/work/repo/src/components/Button.tsx'
  errno: -24,
  code: 'EMFILE',
  syscall: 'open'

Common causes

The file-descriptor ulimit is too low

A runner with a small ulimit -n is exhausted by tools that open many files concurrently.

Too much parallel file access

A wide glob, a watcher over a huge tree, or high test concurrency opens more descriptors than allowed at once.

How to fix it

Raise the open-file limit

Increase the ulimit in the job before the build runs.

workflow

- run: ulimit -n 65536
- run: npm run build

Reduce concurrent file access

Lower test/build parallelism and narrow watchers so fewer descriptors are open at once.

Cap test workers (for example jest --maxWorkers=50%).
Restrict watch globs to the directories you actually need.
Use graceful-fs-style FD queuing where the tool supports it.

How to prevent it

Set a generous ulimit -n in CI for file-heavy builds.
Bound parallelism in test and build steps.
Avoid watching enormous trees in CI.