Linux CentOS 7 SSH Connection Refused after Reboot

Description

On CentOS 7, I am using SSH fine for a month. After doing some operation with "systemctl status/mask/disable/restart firewalld" followed by "sudo reboot -h now", I cannot use ssh and got "connection refused" after reboot.

Problem

ssh 127.0.0.1

connection refused

Log

journalctl -u sshd | tail -100

Bad configuration option:ForwardX11Trusted

ssh failed

Solution

Comment "ForwardX11Trusted" option in sshd_config file as follows.

sudo vi /etc/ssh/sshd_config

X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost no
#ForwardX11Trusted yes

Outcome

journalctl -u sshd | tail -100

-- Logs begin at Tue 2016-11-08 17:45:28 HKT, end at Tue 2016-11-08 17:49:45 HKT. --

Nov 08 17:45:47 pc009 systemd[1]: Started OpenSSH server daemon.

Nov 08 17:45:47 pc009 systemd[1]: Starting OpenSSH server daemon...

Nov 08 17:45:47 pc009 sshd[1033]: Server listening on 0.0.0.0 port 22.

Nov 08 17:45:47 pc009 sshd[1033]: Server listening on :: port 22.

Nov 08 17:45:54 pc009 sshd[2296]: Accepted password for user from 10.1.10.111 port 59915 ssh2