一.查看TCP 22端口是否打开
    netstat -ntpl | grep 22
    [root@localhost ~]# netstat -ntpl | grep 22
    tcp 0 0 0.0.0.0:22 0.0.0.0: LISTEN 155189/sshd
    tcp6 0 0 :::7020 :::     LISTEN 55522/java
    tcp6 0 0 :::22 ::: LISTEN 155189/sshd
    tcp6 0 0 :::8091 :::     LISTEN 55522/java

    二.若没有打开
    找到了 /etc/ssh/ 目录下的sshd服务配置文件 sshd_config，用Vim编辑器打开
    将文件中，关于监听端口、监听地址前的 # 号去除
    [root@localhost ssh]# vi sshd_config
    # $OpenBSD: sshd_config,v 1.103 2018/04/09 20:41:22 tj Exp $
    # This is the sshd server system-wide configuration file. See
    # sshd_config(5) for more information.
    # This sshd was compiled with PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
    # The strategy used for options in the default sshd_config shipped with
    # OpenSSH is to specify options with their default value where
    # possible, but leave them commented. Uncommented options override the
    # default value.
    # If you want to change the port on a SELinux system, you have to tell
    # SELinux about this change.
    # semanage port -a -t ssh_port_t -p tcp #PORTNUMBER
    #
    Port 22
    #AddressFamily any
    #ListenAddress 0.0.0.0
    #ListenAddress ::
    #HostKey /etc/ssh/ssh_host_rsa_key
    #HostKey /etc/ssh/ssh_host_ecdsa_key
    #HostKey /etc/ssh/ssh_host_ed25519_key
    # Ciphers and keying
    #RekeyLimit default none
    # Logging
    #SyslogFacility AUTH
    #LogLevel INFO
    # Authentication:
    #LoginGraceTime 2m
    PermitRootLogin prohibit-password
    #StrictModes yes
    #MaxAuthTries 6
    #MaxSessions 10
    #PubkeyAuthentication yes
    # The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
    # but this is overridden so installations will only check .ssh/authorized_keys
    AuthorizedKeysFile .ssh/authorized_keys
    #AuthorizedPrincipalsFile none
    #AuthorizedKeysCommand none
    #AuthorizedKeysCommandUser nobody
    # For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
    #HostbasedAuthentication no
    # Change to yes if you don’t trust ~/.ssh/known_hosts for
    # HostbasedAuthentication
    #IgnoreUserKnownHosts no
    # Don’t read the user’s ~/.rhosts and ~/.shosts files
    #IgnoreRhosts yes
    # To disable tunneled clear text passwords, change to no here!
    PasswordAuthentication yes
    #PermitEmptyPasswords no
    # Change to no to disable s/key passwords
    #ChallengeResponseAuthentication yes
    # Kerberos options
    #KerberosAuthentication no
    #KerberosOrLocalPasswd yes
    #KerberosTicketCleanup yes
    #KerberosGetAFSToken no
    #KerberosUseKuserok yes
    # GSSAPI options
    #GSSAPIAuthentication no
    #GSSAPICleanupCredentials yes
    #GSSAPIStrictAcceptorCheck yes
    #GSSAPIKeyExchange no
    #GSSAPIEnablek5users no
    # 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
    # PasswordAuthentication. Depending on your PAM configuration,
    # PAM authentication via ChallengeResponseAuthentication may bypass
    # the setting of “PermitRootLogin without-password”.
    # If you just want the PAM account and session checks to run without
    # PAM authentication, then enable this but set PasswordAuthentication
    # and ChallengeResponseAuthentication to ‘no’.
    # WARNING: ‘UsePAM no’ is not supported in Fedora and may cause several
    # problems.
    #UsePAM no
    #AllowAgentForwarding yes
    #AllowTcpForwarding yes
    #GatewayPorts no
    #X11Forwarding no
    #X11DisplayOffset 10
    #X11UseLocalhost yes
    #PermitTTY yes
    #PrintMotd yes
    #PrintLastLog yes
    #TCPKeepAlive yes
    #PermitUserEnvironment no
    #Compression delayed
    #ClientAliveInterval 0
    #ClientAliveCountMax 3
    #UseDNS no
    #PidFile /var/run/sshd.pid
    #MaxStartups 10:30:100
    #PermitTunnel no
    #ChrootDirectory none
    #VersionAddendum none
    # no default banner path
    #Banner none
    # override default of no subsystems
    Subsystem sftp /usr/libexec/openssh/sftp-server

    # Example of overriding settings on a per-user basis
    #Match User anoncvs
    # X11Forwarding no
    # AllowTcpForwarding no
    # PermitTTY no
    # ForceCommand cvs server
    # To modify the system-wide ssh configuration, create a .conf file under
    # /etc/ssh/sshd_config.d/ which will be automatically included below
    Include /etc/ssh/sshd_config.d/    .conf

    三.重启sshd服务
    [root@localhost ssh]# systemctl start sshd

    四.远程工具连接验证