$ sudo apt-get update
$ sudo apt-get install ejabberd-mod-post-log 

ejabberd-mod-post-log is installed in your system.

Make ensure the ejabberd-mod-post-log package were installed using the commands given below,

$ sudo dpkg-query -l | grep ejabberd-mod-post-log *

You will get with ejabberd-mod-post-log package name, version, architecture and description in a table

ejabberd-mod-post-log package basic information: