CentOS SSH安全和配置无密码登录
CentOS ssh默认监听端口 22端口，允许root用户ssh登录。server投入生产后很有必要更改默认ssh监听端口和禁止root登录。
步骤1：确认安装有ssh包
[appuser@su172 ~]$ rpm -qa | egrep -i ssh
openssh-server-5.3p1-114.el6_7.x86_64
openssh-5.3p1-114.el6_7.x86_64
libssh2-1.4.2-1.el6.x86_64
步骤2：可以进一步确认包的默认安装位置信息
appuser@su172 ~]$ rpm -qpl openssh-server-5.3p1-114.el6_7.x86_64
步骤3：主要改动这2个项
[root@su172 ~]# egrep '^Port|^PermitRoot' /etc/ssh/sshd_config
Port 3001
PermitRootLogin no
[root@su172 ~]#
步骤4：重启sshd服务
service sshd restart
步骤5：确认监听端口，客户端验证测试。
#装有ssh 客户端软件，例如Xmanager
ssh 192.168.36.182 3001
#在Linux Server上，可以这样子登录
ssh 192.168.36.182 -p 3001 -l appuser
#示例
[root@su172 ~]# netstat -antlp | egrep -i ssh
tcp 0 0 0.0.0.0:3001 0.0.0.0:* LISTEN 1528/sshd
tcp 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN 1586/sshd
tcp 0 52 192.168.36.182:3001 192.168.36.36:34834 ESTABLISHED 1582/sshd
tcp 0 0 :::3001 :::* LISTEN 1528/sshd
tcp 0 0 ::1:6010 :::* LISTEN 1586/sshd
[root@su172 ~]#
#用w或者who确认
[root@su172 ~]# w
23:09:56 up 1:00, 3 users, load average: 0.00, 0.00, 0.00
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root tty1 - 22:10 14.00s 0.16s 0.16s -bash
appuser pts/0 192.168.36.36 23:04 0.00s 0.10s 0.15s sshd: appuser [priv]
appuser pts/1 192.168.36.181 23:07 2:12 0.01s 0.01s -bash
[root@su172 ~]#
扩展：端口
公认端口（Well Known Ports）从0到1023。
注册端口（RegisteredPorts）从1024到49151。
动态和/或私有端口（Dynamic and/or Private Ports）从49152到65535。
CentOS系统之间有可能需要无密码验证登录，方便拷贝东东，例如oracle rac安装时就有这个东西。所以提前了解很有必要。
node1执行以下步骤：
ssh-keygen -t rsa -P ''
scp /root/.ssh/id_rsa.pub root@192.168.36.182:/root/.ssh/id_rsa.pub181
node2执行以下步骤：
ssh-keygen -t rsa -P ''
scp id_rsa.pub root@192.168.36.181:/root/.ssh/id_rsa.pub182
node1执行：
cat id_rsa.pub182 >>authorized_keys
node2执行
cat id_rsa.pub181 >>authorized_keys
验证
node1验证
ssh 192.168.36.182
node2验证
ssh 192.168.36.181
扩展
-v跟踪
[root@su171 .ssh]# ssh -v 192.168.36.182
OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.36.182 [192.168.36.182] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/identity type -1
debug1: identity file /root/.ssh/identity-cert type -1
debug1: identity file /root/.ssh/id_rsa type 1
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: Remote
protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host '192.168.36.182' is known and matches the RSA host key.
debug1: Found key in /root/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure. Minor code may provide more information
Cannot determine realm for numeric host address
debug1: Unspecified GSS failure. Minor code may provide more information
Cannot determine realm for numeric host address
debug1: Unspecified GSS failure. Minor code may provide more information
debug1: Unspecified GSS failure. Minor code may provide more information
Cannot determine realm for numeric host address
debug1: Next authentication method: publickey
debug1: Trying private key: /root/.ssh/identity
debug1: Offering public key: /root/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
Last login: Thu May 12 23:51:22 2016 from 192.168.36.181
[root@su172 ~]#
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