[core:notice] [pid 15284] AH00051: child pid 15288 exit signal Floating point exception (8), possible coredump in /etc/apache2 error
There was only ERR_EMPTY_RESPONSE at the front end and the above error in the apache error logwhile setting up D7 client site in my local PHP 7.1 dev evironment. So I knew the error was due to some php extension crashing and needed the backtrace through the coredump as said in the error notice to get to the root cause.
First I searched through the /etc/apache2 folder to get the coredump but there wasn’t any. So It was definitely some permission with the folder (/etc/apache2 has root owner) which prevented apache from writing to the file. So I had to change the coredump directory. This can be done by adding the directory in /etc/apache2/apache2.conf, below I have given /tmp.
Then you will get the coredump in the tmp directory and we can analyze it using gdb
sudo gdb apache2 core_dump_name
Write bt in the interactive cli of gdb to get the backtrace. There I got the error was due to opcache crashing and disabled it for the D7 site in Virtual Host for the site.
php_flag opcache.enable Off
The site was back when I restarted the apache2 service. Thats it!