Some quick notes on manually moving LibreNMS to a new server.  For more detailed instructions you can refer to the following post

Recovering LibreNMS from crashed XenServer VM

Steps

1. Backup /opt/librenms file
2. Backup librenms database
3. Install LibreNMS on new server
4. Import /opt/librenms files
5. Import librenms database

Backing up LibreNMS files

LibreNMS stores all it’s files in /opt/librenms
Quick and easy way to back up the LibreNMS files is to use tar.

tar zcvf librenms_backup.tgz /opt/librenms

Migrating Database

I believe you can copy the whole /var/lib/mysql directory.  Should be able to use the above command.  If not you can do a mysqldump and then import it on the new system.