2、增强服务器安全等级——修改服务器默认登录端口

我们默认通过ssh登录的端口是22，这个端口是默认的也就意味着这个端口对于所有人是透明的，如果你买台服务器，没有经过修改的话，那别人就等于已经猜到你的登录端口是22。出于基本的安全考虑，我们是需要修改一下这个端口的。

1、修改配置文件： /etc/ssh/sshd_config

配置文件中的内容：

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#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
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 1024

# Logging
LogLevel INFO

# Authentication:
LoginGraceTime 120
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

# 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

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PAM authentication via ChallengeResponseAuthentication may bypass
# If you just want the PAM account and session checks to run without
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes
UseDNS no
AddressFamily inet
PermitRootLogin yes
SyslogFacility AUTHPRIV
PasswordAuthentication yes

2、在改之前需要先新建一个连接窗口，保持登录状态，防止修改失败导致ssh连不上。

3、端口的范围是0-65536

由于0-1024最好不要使用，因为这些可能是被系统默认占用的端口，所以我们配置端口时为了避免和系统端口冲突，最好采用1024以后的端口。

端口号改成39999

UseDNS保证为no

底部加一行允许登录的用户

重启ssh

测试：

尝试用22连接被拒绝

使用39999端口登录成功

如果登录依然不成功的话，可能是阿里云的安全组配置规则需要修改：

具体可参考文档：
https://yq.aliyun.com/articles/168203

4、修改配置文件，不允许root用户登录：

修改配置文件中PermitRootLogin为no