[BUG] Claude Code (Bun runtime) fails with getaddrinfo ETIMEOUT when /etc/resolv.conf has trailing inline comments on nameserver lines

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code fails to authenticate with:

Login failed: getaddrinfo ETIMEOUT platform.claude.com

This is reproducible identically via claude auth login from a plain terminal (no VS Code involved), so the issue is isolated to Claude Code's own runtime, not the extension or VS Code integration.

At the same time, on the identical machine and network:

• curl -4 and curl -6 to https://platform.claude.com both succeed instantly
• nslookup/dig against all 3 configured nameservers succeed in <50ms each

This points to Claude Code's bundled Bun runtime (confirmed via /$bunfs/root/src/entrypoints/cli.js appearing in error stack traces) using its own DNS resolver rather than glibc's getaddrinfo, and that resolver behaving differently from every standard system tool.

Root Cause Identified

The cluster's /etc/resolv.conf, managed by Quattor, contains trailing inline comments on each nameserver line:

Generated by NetworkManager
search example.edu
nameserver 10.0.0.1               # added by Quattor
nameserver 10.0.0.2               # added by Quattor
nameserver 203.0.100.3                  # added by Quattor  

Confirmed fix: removing the trailing # added by Quattor comments from each nameserver line (moving them to their own separate comment lines, or removing them entirely) immediately resolved the issue — Claude Code login succeeded right after.

The cluster's config management system (Quattor) will regenerate resolv.conf with these comments on future updates, so this fix is temporary and the bug will recur. This is not something that can be permanently fixed on the client/cluster side without an ongoing manual workaround.

What Should Happen?

Claude Code's DNS resolution should tolerate trailing comments in /etc/resolv.conf, consistent with resolv.conf(5) parsing behavior in glibc and virtually every other standard tool (curl, nslookup, dig, Node.js's dns.lookup()).

Error Messages/Logs

Steps to Reproduce

1. On a Linux host with /etc/resolv.conf containing trailing inline comments after nameserver directives (e.g. nameserver 1.2.3.4 # some comment)
2. Run claude auth login
3. Observe getaddrinfo ETIMEOUT on the OAuth callback domain, despite curl/nslookup/dig all succeeding against the same domain and nameservers

Environment

• OS (remote, running Claude Code): Linux (HPC cluster, Quattor-managed configuration)
• Connection: SSH (VS Code Remote-SSH)

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.212

Platform

Other

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

Related Issues

This may be related to

• https://github.com/anthropics/claude-code/issues/72706
• https://github.com/anthropics/claude-code/issues/71824

which reports the same underlying symptom ("Claude Code's bundled DNS resolver fails on Anthropic domains, but the
system resolver (used by curl) works") without a confirmed root cause.