First off: this is no duplicate as the solution provided differs from any solution for similar questions and "[notice] child pid XXXX exit signal Segmentation fault (11)" in apache error.log does not accept any more answers. Also I cannot comment on SO yet.
I just upgraded from PHP-7.0 to PHP-7.3 (or any version combo for that matter) and am now getting
[notice] child pid XXXX exit signal Segmentation fault (11)
in my apache error.log file.
Other solutions to this question did not apply:
TIA
Check whether your PHP-FPM and PHP versions match. Make sure there is a (correct) PHP-FPM configuration corresponding to your PHP and PHP-FPM version, respectively.
On a Debian system there should be something like this:
/etc/php/7.3/fpm
/etc/php/7.3/fpm/php.ini
/etc/php/7.3/fpm/php-fpm.conf
/etc/php/7.3/fpm/pool.d
/etc/php/7.3/fpm/conf.d
/etc/php/7.3/fpm/pool.d/www.conf
On my system the /etc/php/7.3/fpm directory was missing. Reason: legacy PHP-FPM didn't get updated. After installing the PHP-FPM update and synch'ing the new fpm config w/ my tweaked config there were no more segfaults and everything started working as it did before the update.
The root cause for those child segfaults was particularly nasty to isolate, maybe this SO answer can save others the hassle.
HTH