Resolved Plugins in Roundcube

[CobraArbok]

I've a VPS with Ubuntu 18.04 LTS.
I need to install some plugin in Roundcube, but in /usr/share/psa-roundcube/config/config.inc.php the key is empty ($config = array(); )
Maybe there is another configuration file, but where?

Which plugins are already installed?
Is it possible to install sieve?

Thanks in advance.

 

[IgorG]

but where?

Plesk for Linux services logs and configuration files

Is it possible to install sieve?

Resolved - Roundcube Sieve Plugin not working, 17.8.11 MU 1

 

[CobraArbok]

Many thanks.
Sieve appears to be already installed and configured.