How to fix error when restarting apache2.4 - php

Question

I have multiple php versions installed on my Ubuntu 18.04 - php7.1 php5.6
When I'm using php7.1 apache restarts successfully.
But when I switch to php5.6 using this command:
sudo a2dismod php7.1 ; sudo a2enmod php5.6 ; sudo service apache2 restart
Apache gives me this error:
Job for apache2.service failed because the control process exited with error code.
See "systemctl status apache2.service" and "journalctl -xe" for details.
systemctl status apache2.service result:
● apache2.service - The Apache HTTP Server
Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
Drop-In: /lib/systemd/system/apache2.service.d
└─apache2-systemd.conf
Active: failed (Result: exit-code) since Sat 2018-10-27 13:19:32 +06; 7s ago
Process: 6458 ExecStart=/usr/sbin/apachectl start (code=exited, status=139)
Oct 27 13:19:32 protectedfor apachectl[6458]: AH00112: Warning:
DocumentRoot [/home/protectedfor/scj] does not exist
Oct 27 13:19:32 protectedfor apachectl[6458]: AH00112: Warning:
DocumentRoot [/var/www/worldclass/worldclass.kg] does not exist
Oct 27 13:19:32 protectedfor apachectl[6458]: [Sat Oct 27 13:19:32.683512 2018] [alias:warn] [pid 6469] AH00671: The Alias directive in /etc/apache2/apache2.conf at line
Oct 27 13:19:32 protectedfor apachectl[6458]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerNa
Oct 27 13:19:32 protectedfor apachectl[6458]: Segmentation fault (core dumped)
Oct 27 13:19:32 protectedfor apachectl[6458]: Action 'start' failed.
Oct 27 13:19:32 protectedfor apachectl[6458]: The Apache error log may have more information.
Oct 27 13:19:32 protectedfor systemd[1]: apache2.service: Control process exited, code=exited status=139
Oct 27 13:19:32 protectedfor systemd[1]: apache2.service: Failed with result 'exit-code'.
Oct 27 13:19:32 protectedfor systemd[1]: Failed to start The Apache HTTP Server.
Apache log:
[Sat Oct 27 12:43:02.172511 2018] [mpm_prefork:notice] [pid 6518] AH00169: caught SIGTERM, shutting down
[Sat Oct 27 12:43:10.498278 2018] [so:warn] [pid 5126] AH01574: module php7_module is already loaded, skipping
[Sat Oct 27 12:43:10.544626 2018] [mpm_prefork:notice] [pid 5137] AH00163: Apache/2.4.29 (Ubuntu) configured -- resuming normal operations
[Sat Oct 27 12:43:10.544656 2018] [core:notice] [pid 5137] AH00094: Command line: '/usr/sbin/apache2'
[Sat Oct 27 12:43:28.243406 2018] [mpm_prefork:notice] [pid 5137] AH00169: caught SIGTERM, shutting down
Any advices really appreciated. Thanks!

Answer 1

Its not just disable the module. You have to set some defaults in order to make that work
Please try this
set from 7.x to 5.x
sudo a2dismod php7.1
sudo a2enmod php5.6
sudo update-alternatives --set php /usr/bin/php5.6
sudo update-alternatives --config php
sudo update-alternatives --set phar /usr/bin/phar5.6
sudo systemctl restart apache2
set from 5.x to 7.x
sudo a2enmod php7.1
sudo a2dismod php5.6
sudo update-alternatives --set php /usr/bin/php7.1
sudo systemctl restart apache2