[Bug]: [macOS] PHP-FPM workers crash with SIGSEGV in gettext() → libintl → CFPreferences (fork-unsafe macOS API) #1656
Description
Platform
macOS
Operating system version
macOS Tahoe 26.3 (25D125)
System architecture
ARM64 (M1, M2, etc)
Herd Version
1.26.1
PHP Version
No response
Bug description
Description
PHP-FPM worker processes crash with a segmentation fault (signal 11) on specific pages when using Herd. The same pages load correctly with php artisan
serve. The issue affects all PHP versions (tested on 8.2, 8.3, 8.4, 8.5) and is not project-specific (reproduced across multiple Laravel projects
including Filament-based ones).
No PHP-FPM log entries are generated — the crash is silent from Herd's perspective, but macOS generates a crash report in
~/Library/Logs/DiagnosticReports/php83-fpm-*.ips.
Environment
- Platform: macOS 26.3 Tahoe (Apple Silicon / ARM64)
- Herd Version: latest
- PHP Versions affected: 8.2, 8.3, 8.4, 8.5
Symptoms
- 502 Bad Gateway on certain pages (not all)
- php artisan serve works fine for the same pages
- Nginx error log shows: upstream prematurely closed connection while reading response header from upstream
- php-fpm.log is empty — no errors logged
- macOS crash report generated: ~/Library/Logs/DiagnosticReports/php83-fpm-*.ips
Root Cause
The crash report reveals a SIGSEGV in PHP-FPM worker processes caused by gettext() calling macOS CoreFoundation APIs that are not fork-safe:
gettext()
→ libintl_dcigettext
→ _libintl_locale_name_default
→ CFPreferencesCopyAppValueWithContainerAndConfiguration ← macOS CoreFoundation
→ -[_CFXPreferences withSearchListForIdentifier:...]
→ dispatch_apply (GCD, multi-threaded)
→ SIGSEGV (EXC_BAD_ACCESS / KERN_INVALID_ADDRESS)
The crash note in the .ips file confirms the fork context:
"asi": {
"CoreFoundation": ["*** multi-threaded process forked ***"],
"libsystem_c.dylib": ["crashed on child side of fork pre-exec"]
}
When libintl needs to determine the system locale at runtime, it calls CFPreferences via Grand Central Dispatch (GCD). GCD dispatch queues inherited from
the PHP-FPM master process are in an invalid state in forked child workers, leading to the crash. php artisan serve is unaffected because it uses the CLI
SAPI and does not fork.
Workaround
Adding locale environment variables to each PHP-FPM pool configuration file prevents libintl from querying CFPreferences at runtime, since the locale is
already defined in the environment:
File: ~/Library/Application Support/Herd/config/fpm/{version}-fpm.conf
(repeat for all installed versions: 8.2, 8.3, 8.4, 8.5)
env[LANG] = en_US.UTF-8
env[LC_ALL] = en_US.UTF-8
Then restart PHP services in Herd. The 502 errors stop immediately.
Suggested Fix
Herd should include LANG and LC_ALL environment variable defaults in the generated FPM pool configuration files, or pass them when spawning PHP-FPM worker
processes. This would prevent the fork-unsafe CFPreferences call that crashes the workers on macOS.
Note: This was diagnosed by inspecting crash reports in ~/Library/Logs/DiagnosticReports/ — the fact that php-fpm.log remains empty makes this very hard
to debug without knowing where to look. Better crash logging or a diagnostic tool in Herd would help surface this kind of issue.
Steps to reproduce
No response