The instructions in Sphinxsearch Installation Instructions are likely out of date. A decent reference source is [How To Install and Configure Sphinx on Ubuntu 16.04 | DigitalOcean|https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-sphinx-on-ubuntu-16-04#step-4-managing-the-index]. 

At a minimum the instructions in 6.1.2.6. Incremental Updates should have the admin check if their distributions pre-configured cron setup for Sphinxsearch.

For example, Ubuntu 24.04 ships with /etc/cron.d/sphinxsearch that contains:

# Rebuild all indexes daily and notify searchd.

@daily      sphinxsearch . /etc/default/sphinxsearch && if [ "$START" = "yes" ] && [ -x /usr/bin/indexer ]; then /usr/bin/indexer --quiet --rotate --all; fi# Example for rotating only specific indexes (usually these would be part of

# a larger combined index).# */5 * * * * sphinxsearch [ -x /usr/bin/indexer ] && /usr/bin/indexer --quiet --rotate postdelta threaddelta