CoreContainer is either not initialized or shutting down error

[shacky <sh...@gmail.com>]

Hi.
I am installing a new SolrCloud cluster with Solr 6.1.0 on Debian 8 Jessie.
I am using Zookeeper from official Debian repository (Zookeeperd
3.4.5+dfsg-2).
I configured and bootstrapped the new cluster, but I'm still getting the
"org.apache.solr.common.SolrException: Error processing the request.
CoreContainer is either not initialized or shutting down." error when I try
to access the admin web UI.

I uploaded solr.xml on Zookeeper:
--------------------------------------------------8<----------------------------------------------
root@staging-index-1:/opt/solr/server/scripts/cloud-scripts#
/usr/share/zookeeper/bin/zkCli.sh
Connecting to localhost:2181
Welcome to ZooKeeper!
JLine support is enabled

WATCHER::

WatchedEvent state:SyncConnected type:None path:null
[zk: localhost:2181(CONNECTED) 0] ls /
[zookeeper, solr]
[zk: localhost:2181(CONNECTED) 1] ls /solr
[solr.xml]
[zk: localhost:2181(CONNECTED) 2]
--------------------------------------------------8<----------------------------------------------

I configured my solr.in.sh as following:
--------------------------------------------------8<----------------------------------------------
ZK_HOST="solr1:2181,solr2:2181,solr3:2181/solr"
SOLR_HOST="solr1"
SOLR_PID_DIR="/var/solr"
SOLR_HOME="/var/solr/data"
LOG4J_PROPS="/var/solr/log4j.properties"
SOLR_LOGS_DIR="/var/solr/logs"
SOLR_PORT="8983"
--------------------------------------------------8<----------------------------------------------

Zookeepers are installed on the same Solr nodes.
I tried to restart Zookeeper and Solr as well, but the problem is still
here.

Could you help me please?

Thank you very much!
Bye