Resolving "./zookeeper.out: Permission denied" error

When starting zookeeper, using the following command

sudo -u zookeeper $ZOOKEEPER_HOME/bin/zkServer.sh start

I saw this error:

Starting zookeeper ... /usr/local/zookeeper/bin/zkServer.sh: line 105: ./zookeeper.out: Permission denied

I resolved this error by telling zookeeper where I wanted the log file to be placed. Simply edit $ZOOKEEPER_HOME/zkEnv.sh, then add this assignment at the top of the file:

ZOO_LOG_DIR=/var/log/zookeeper

Then create that directory:

sudo mkdir /var/log/zookeeper
sudo chown zookeeper /var/log/zookeeper