Support for this functions are not enabled by default. To enable System V semaphore support compile PHP with the option --enable-sysvsem. To enable the System V shared memory support compile PHP with the option --enable-sysvshm. To enable the System V messages support compile PHP with the option --enable-sysvmsg.
It should be mentioned that depending on the system, an module can be available.
On CentOS I just ran:
sudo yum install php73-php-sysvsem
then reload:
sudo service php-fpm reload (or apache, depending on your case)
and semaphore functions are now available.
