Ubuntu中使用命令：
$sudo apt-get install openssh-server openssh-client
$sudo apt-get install openssh-server openssh-clientCentOS中使用命令：
$sudo yum install openssh-server openssh-client
$sudo yum install openssh-server openssh-client启动ssh使用命令：
$sudo service sshd start
$sudo service sshd start二、配置无密码登录SSH
Ubuntu中配置如下：
$ ssh-keygen -t dsa -P ''
Generating public/private dsa key pair.
Enter file in which to save the key (/home/aaron/.ssh/id_dsa):
Created directory '/home/aaron/.ssh'.
Your identification has been saved in /home/aaron/.ssh/id_dsa.
Your public key has been saved in /home/aaron/.ssh/id_dsa.pub.
The key fingerprint is:
bd:2c:ed:ab:6d:a9:b2:45:88:32:08:5a:d2:d9:ad:cc aaron@ubuntu
The key's randomart image is:
+--[ DSA 1024]----+
| |
| . o . |
|o + . . |
|o+ o o . . |
|o o E . S . |
| o . o . |
| o +. |
| .. +o |
| .oo++. |
+-----------------+
$ ssh-keygen -t dsa -P '' Generating public/private dsa key pair. Enter file in which to save the key (/home/aaron/.ssh/id_dsa): Created directory '/home/aaron/.ssh'. Your identification has been saved in /home/aaron/.ssh/id_dsa. Your public key has been saved in /home/aaron/.ssh/id_dsa.pub. The key fingerprint is: bd:2c:ed:ab:6d:a9:b2:45:88:32:08:5a:d2:d9:ad:cc aaron@ubuntu The key's randomart image is: +--[ DSA 1024]----+ | | | . o . | |o + . . | |o+ o o . . | |o o E . S . | | o . o . | | o +. | | .. +o | | .oo++. | +-----------------+（注：回车后会在~/.ssh/下生成两个文件：id_rsa和id_rsa.pub。这两个文件是成对出现的。）
将id_dsa.pub里面的内容加到用于认证的公钥文件中，命令如下：
$ cat id_dsa.pub >> authorized_keys
$ cat id_dsa.pub >> authorized_keys可以将这个生成的authorized_keys拷贝到别的机器上面
$ cat ~/.ssh/authorized_keys | \
ssh aarron@192.168.1.108 "cat - >> ~/.ssh/authorized_keys"
$ cat ~/.ssh/authorized_keys | \ ssh aarron@192.168.1.108 "cat - >> ~/.ssh/authorized_keys"登录localhost。在终端输入命令：ssh localhost(注：当ssh远程登录到其它机器后，你控制的是远程的机器，需要执行退出命令才能重新控制本地主机。)执行退出命令。输入命令：exit
如果配置过程中出现问题，一般的问题都是文件权限设置的不对，请把.ssh和authorized_keys的访问权限分别设置为755个600，命令如下：
$ chmod 755 ~/.ssh
$ chmod 600 ~/.ssh/authorized_keys
$ chmod 755 ~/.ssh $ chmod 600 ~/.ssh/authorized_keys上面是以Ubuntu平台为例子，下面来说说怎么在CentOS平台上面配置。
首先，需要设置一下/etc/ssh/sshd_config文件，请将/etc/ssh/sshd_config文件中下面三行的注释去掉：
$sudo vim /etc/ssh/sshd_config
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
$sudo vim /etc/ssh/sshd_config RSAAuthentication yes PubkeyAuthentication yes AuthorizedKeysFile .ssh/authorized_keys其余的步骤和在Ubuntu下配置是一样的。
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