$ sudo /etc/init.d/ssh restart

$ sudo ufw disable
$ sudo ufw status
状態： 非アクティブ

ListenAddress 0.0.0.0

# Package generated configuration file
# See the sshd(8) manpage for details
# What ports, IPs and protocols we listen for

#==========================================================
# デフォルトのポートを使わないのを習慣づけよう(22⇒****)
Port 22
#----------------------------------------------------------
# フォーラムのアドバイスでwell known port（22）に戻してみる
# Port ****
#==========================================================

# Use these options to restrict which interfaces/protocols sshd will bind to
#=====================================================
# 許可するアドレスを指定します
# デフォルトでは全てのローカルアドレスが有効らしい
#-----------------------------------------------------
#ListenAddress ::
#ListenAddress 0.0.0.0
#=====================================================

Protocol 2

# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120

#======================================
# ルートによるログインを禁止(yes⇒no)
# PermitRootLogin yes
#---------------------------------------
PermitRootLogin no
#=======================================

StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile    %h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
#=============================================
# パスワードによる認証を禁止します(yes⇒no)
#PasswordAuthentication yes
#---------------------------------------------
PasswordAuthentication no
#=============================================

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

UsePAM yes


#======================================================
# フォーラムのアドバイスで、DNSをOFFにしてみる
# リモートホスト名の解決にDNSを使用しなくなるとのこと。
#------------------------------------------------------
UseDNS no
#======================================================

#===========================================
# 念のためアクセスできるユーザーを制限
# 例)
# AllowUsers ******* hoge1 hoge2
#-------------------------------------------
AllowUsers ******* *********
#===========================================