ssh有两种连接方式
第一种：密码认证连接方式
[root@admin ~]# ssh root@192.168.1.25 (服务端的ip回车提示如下）
The authenticity of host ‘192.168.1.250 (192.168.1.250)‘ can‘t be established.
RSA key fingerprint is 75:f9:55:3b:da:0d:38:b2:c6:1b:e9:18:96:97:8a:2e.
Are you sure you want to continue connecting (yes/no)?（这里输入yes保证密钥回车）
Warning: Permanently added ‘192.168.1.250‘ (RSA) to the list of known hosts.
root@192.168.1.25‘s password:（输入密码回车）
第二种：密钥连接方式
[root@admin ~]# ssh-keygen（启动密钥连接方式）
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): (保持密钥的地方默认是保
存在当前用户目录下如需
修改，输入保持地址）
Enter passphrase (empty for no passphrase): （是否使用密码使用默认回车）
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
e4:4d:4c:b7:e4:ec:07:d5:a7:f0:3c:a0:b0:1f:98:a1 root@admin
The key‘s randomart image is:
+--[ RSA 2048]----+
| . o .. |
| oo =oo o|
| ..*o.== ..|
| Eo+oo. .= |
| S.... .. |
| . . |
| |
| |
| |
+-----------------+
密钥生成之后进入.ssh/目录会看到
[root@admin ~]# cd .ssh/
[root@admin .ssh]# ls
id_rsa id_rsa.pub known_hosts（id_rsa.pub)这个文件就是密钥认证文件
[root@admin .ssh]# ssh-copy-id -i id_rsa.pub root@192.168.1.25(把密钥发送给服务端）
root@192.168.1.25‘s password:（输入服务端密码）输入回车提示如下就成功了
Now try logging into the machine, with "ssh ‘root@192.168.1.25‘", and check in:
.ssh/authorized_keys
to make sure we haven‘t added extra keys that you weren‘t expecting.
备注：如果系统装或发生其它不能正常连接的情况把.ssh/目录下的文件删除重新配置即可
如果想比较安全或控制用户登录进入cd /etc/ssh会看到
[root@admin .ssh]# cd /etc/ssh
[root@admin ssh]# ls
moduli ssh_host_dsa_key ssh_host_key.pub
ssh_config ssh_host_dsa_key.pub ssh_host_rsa_key
sshd_config ssh_host_key ssh_host_rsa_key.pub
ssh_config这个是客户端配置文件不用管，sshd_config这个是服务端配置文件修改这个就行
用vim打开ssh_config
SyslogFacility AUTHPRIV
#LogLevel INFO
# Authentication:
#LoginGraceTime 2m
#PermitRootLogin yes(把这个改成no禁止用root登录）
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10
# To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes
#PermitEmptyPasswords no
PasswordAuthentication yes（打这个改成no不能使用密码验证）
原文地址：http://nakedman.blog.51cto.com/7350188/1730943
