用root 用户可以正常xhost + ,xclock 显示图形化界面，
而oracle 用户图形化提示 no protocol specified
办法是：直接用oracle 用户xshell登录，不要root 切换过去。
Connecting to 192.168.56.131:22...
Connection established.
To escape to local shell, press 'Ctrl+Alt+]'.
Connection established.
To escape to local shell, press 'Ctrl+Alt+]'.
/usr/bin/xauth: creating new authority file /home/oracle/.Xauthority
[oracle@hdp-03 ~]$ xhost +
access control disabled, clients can connect from any host
[oracle@hdp-03 ~]$ cd /opt/database/
[oracle@hdp-03 database]$ ls
install response rpm runInstaller sshsetup stage welcome.html
[oracle@hdp-03 database]$ env|grep DISPLAY
DISPLAY=localhost:10.0
[oracle@hdp-03 database]$ xhost +
access control disabled, clients can connect from any host
[oracle@hdp-03 ~]$ xhost +
access control disabled, clients can connect from any host
[oracle@hdp-03 ~]$ cd /opt/database/
[oracle@hdp-03 database]$ ls
install response rpm runInstaller sshsetup stage welcome.html
[oracle@hdp-03 database]$ env|grep DISPLAY
DISPLAY=localhost:10.0
[oracle@hdp-03 database]$ xhost +
access control disabled, clients can connect from any host
最后，如果还是不行，那就只能放大招了，看是否xshell4版本太低了，
换xshell5试试吧