[BUG] claude segfaults on startup (glibc 2.44, EndeavourOS/Arch) — Bun runtime crash in newlocale/free during pthread_once init

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?

Environment

• Claude CLI version: 2.1.243 (also reproduced on 2.1.112 — not version-specific)
• Operating System: EndeavourOS (Arch-based rolling release)
• glibc version: 2.44 (ldd (GNU libc) 2.44)
• Kernel: 6.18.44-fc-v21 (custom build)
• CPU: AMD Ryzen 7 7435HS — confirmed AVX2, BMI2, FMA all present (not a baseline-build CPU issue)
• Terminal: Konsole
• Platform: Anthropic API (not Bedrock/Vertex)
• Install method: npm global install (~/.local/bin/claude)

Bug Description

claude and claude --version segfault immediately on

What Should Happen?

Expected Behavior

claude --version prints the version string and exits 0.

Actual Behavior

Segfault (SIGSEGV) on every invocation, no stdout output at all.

Error Messages/Logs

$ claude --version
Segmentation fault      (core dumped) claude --version

$ coredumpctl list claude
Tue 2026-08-25 13:38:47 CEST 169643 1000 1000 SIGSEGV present  /home/shifu/.local/share/claude/versions/2.1.243 70.7M

$ coredumpctl gdb claude
           PID: 169643 (claude)
           TID: 169643 (claude)
           UID: 1000 (shifu)
           GID: 1000 (shifu)
        Signal: 11 (SEGV)
     Timestamp: Tue 2026-08-25 13:38:47 CEST
  Command Line: /home/shifu/.local/bin/claude --version
    Executable: /home/shifu/.local/share/claude/versions/2.1.243
       Message: Process 169643 (claude) of user 1000 dumped core.

                Stack trace of thread 169643:
                #0  0x0000000001d10458 free (2.1.243 + 0x1b10458)
                #1  0x00007f5c7ee3530a __newlocale (libc.so.6 + 0x3530a)
                #2  0x0000000001abd282 n/a (2.1.243 + 0x18bd282)
                #3  0x00007f5c7ee9d69c n/a (libc.so.6 + 0x9d69c)
                #4  0x00007f5c7ee9d719 pthread_once (libc.so.6 + 0x9d719)
                #5  0x0000000001abc2d2 n/a (2.1.243 + 0x18bc2d2)
                #6  0x0000000001ace6cf n/a (2.1.243 + 0x18ce6cf)
                #7  0x0000000001abdc0a n/a (2.1.243 + 0x18bdc0a)
                #8  0x0000000001abe9c4 n/a (2.1.243 + 0x18be9c4)
                #9  0x00007f5c7ee9d69c n/a (libc.so.6 + 0x9d69c)
                #10 0x00007f5c7ee9d719 pthread_once (libc.so.6 + 0x9d719)
                #11 0x0000000001abea15 n/a (2.1.243 + 0x18bea15)
                #12 0x0000000001abead7 n/a (2.1.243 + 0x18bead7)
                #13 0x0000000001abb922 n/a (2.1.243 + 0x18bb922)
                #14 0x0000000001abb724 n/a (2.1.243 + 0x18bb724)
                #15 0x0000000001aadadd n/a (2.1.243 + 0x18adadd)
                #16 0x00007f5c7ee27892 __libc_start_main (libc.so.6 + 0x27892)
                #17 0x0000000001953a2e n/a (2.1.243 + 0x1753a2e)

(gdb) bt
#0  0x0000000001d10458 in free ()
#1  0x00007f5c7ee3530a in newlocale () from /usr/lib/libc.so.6
#2  0x0000000001abd282 in ?? ()
#3  0x00007f5c7ee9d69c in ?? () from /usr/lib/libc.so.6
#4  0x00007f5c7ee9d719 in pthread_once () from /usr/lib/libc.so.6
#5  0x0000000001abc2d2 in ?? ()
#6  0x0000000001ace6cf in ?? ()
#7  0x0000000001abdc0a in ?? ()
#8  0x0000000001abe9c4 in ?? ()
#9  0x00007f5c7ee9d69c in ?? () from /usr/lib/libc.so.6
#10 0x00007f5c7ee9d719 in pthread_once () from /usr/lib/libc.so.6
#11 0x0000000001abea15 in ?? ()
#12 0x0000000001abead7 in ?? ()
#13 0x0000000001abb922 in ?? ()
#14 0x0000000001abb724 in ?? ()
#15 0x0000000001aadadd in ?? ()
#16 0x00007f5c7ee27892 in __libc_start_main () from /usr/lib/libc.so.6
#17 0x0000000001953a2e in ?? ()

Steps to Reproduce

Steps to Reproduce

1. Fresh EndeavourOS system with glibc 2.44
2. npm install -g @anthropic-ai/claude-code
3. Run claude --version
4. Immediate Segmentation fault (core dumped)

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown — tested 2.1.112 and 2.1.243, both segfault identically. No version has been confirmed working on this host's glibc 2.44. Works correctly inside a node:20-bookworm Docker container (glibc 2.36) at the current version.

Claude Code Version

2.1.243

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

Troubleshooting already performed

• Ruled out version regression: downgraded to 2.1.112 — still segfaults identically. Not specific to a recent build.
• Ruled out CPU baseline mismatch: confirmed AVX2, BMI2, FMA all present via /proc/cpuinfo. This is not the "baseline build on modern CPU" issue seen in #76241.
• Ruled out locale mismatch: system has mixed LANG=en_US.UTF-8 with several LC_* categories set to it_IT.UTF-8. Tested LC_ALL=C.UTF-8 claude --version — still segfaults identically. Locale mismatch is not the trigger (despite the crash occurring inside newlocale).
• Ruled out shell/env pollution: ran with env -i HOME=$HOME PATH=/usr/bin:/bin /home/shifu/.local/bin/claude --version — still segfaults.
• Ruled out network/API issue: crash is instant and identical whether network is up or not, and occurs on --version which shouldn't need network.
• Ruled out binary corruption: file confirms a valid, non-stripped ELF64 dynamically linked executable; fresh reinstall via npm made no difference.
• Confirmed workaround: running Claude Code inside a node:20-bookworm Docker container (glibc 2.36) works with zero issues — same npm install, same version, no crash. This strongly points to a glibc-version incompatibility rather than anything project- or config-specific.