Adapted MIAB Solr install script from https://github.com/jkaberg/ for Ubuntu Bionic

conf/cronjob/dovecot

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+/usr/bin/doveadm fts rescan -A

conf/cronjob/solr

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+*/1 * * * * root /usr/bin/curl http://127.0.0.1:8080/solr/update?commit=true &>/dev/null
+30 3 * * * root /usr/bin/curl http://127.0.0.1:8080/solr/update?optimize=true &>/dev/null

setup/solr.sh

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+#!/bin/bash
+#
+# Inspired by the solr.sh from jkaberg (https://github.com/jkaberg/mailinabox-sogo)
+# with some modifications
+#
+# IMAP search with lucene via solr
+# --------------------------------
+#
+# By default dovecot uses its own Squat search index that has awful performance
+# on large mailboxes. Dovecot 2.1+ has support for using Lucene internally but
+# this didn't make it into the Ubuntu packages, so we use Solr instead to run
+# Lucene for us.
+#
+# Solr runs as a tomcat process. The dovecot solr plugin talks to solr via its
+# HTTP interface, causing mail to be indexed when searches occur, and getting
+# results back.
+
+source setup/functions.sh # load our functions
+source /etc/mailinabox.conf # load global vars
+
+# Install packages and basic configuation
+# ---------------------------------------
+
+echo "Installing Solr..."
+
+# Install packages
+apt_install solr-tomcat dovecot-solr
+
+# Solr requires a schema to tell it how to index data, this is provided by dovecot
+cp /usr/share/dovecot/solr-schema.xml /etc/solr/conf/schema.xml
+
+# Update the dovecot plugin configuration
+#
+# Break-imap-search makes search work the way users expect, rather than the way
+# the IMAP specification expects
+tools/editconf.py /etc/dovecot/conf.d/10-mail.conf \
+        mail_plugins="fts fts_solr"
+
+cat > /etc/dovecot/conf.d/90-plugin-fts.conf << EOF;
+plugin {
+  fts = solr
+  fts_autoindex = yes
+  fts_solr = break-imap-search url=http://127.0.0.1:8080/solr/
+}
+EOF
+
+# Bump memory allocation for Solr.
+# Not needed? I'll let it sit here for a while.
+#echo 'export JAVA_OPTS=-Xms512M -Xmx1024M' > /usr/share/tomcat7/bin/setenv.sh
+
+# Install cronjobs to keep FTS up to date
+hide_output install -m 755 conf/cronjob/dovecot /etc/cron.daily/
+hide_output install -m 644 conf/cronjob/solr /etc/cron.d/
+
+# PERMISSIONS
+
+# Ensure configuration files are owned by dovecot and not world readable.
+chown -R mail:dovecot /etc/dovecot
+chmod -R o-rwx /etc/dovecot
+
+# Restart services to reload solr schema & dovecot plugins
+restart_service tomcat8
+restart_service dovecot