update: 下面這篇文章距離現在比較久了，不一定適合大家機器現在的情況了，如果不能成功解決問題請見諒。

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簡單地說

配置hadoop時必須的一步就是保證ssh是聯通的。如果你的ubuntu中沒有安裝ssh，具體的安裝步驟是這樣的:

下載檔案” openssh-client_5.3p1-3ubuntu3_i386.deb”並在終端中安裝。

sudo dpkg -i openssh-client_5.3p1-3ubuntu3_i386.deb

複雜地說

我嘗試了很多錯誤路線，最後終於找到了正確方式，現在把我走過的彎路也記錄一下

在hadoop配置的過程中，前提條件之一是保證ssh是配置好的。使用這個命令，[email protected]:~$ ssh localhost

得到了如下的資訊

ssh: connect to host localhost port 22: Connection refused這意味著ssh不能聯通成功。不聯通的理由可以有很多，如防火牆設定問題，如ssh沒有被安裝。我的連防火牆都沒有，所以應該是ssh安裝的問題。

於是現在安裝ssh
網上搜到資訊說，安裝ssh應該使用這樣的命令，如下

[email protected]:~$ sudo apt-get install openssh-server

於是，自然而然地想到要去安裝1:5.3p1-3ubuntu，

[email protected]:~$ sudo apt-get install 1:5.3p1-3ubuntu3
Reading package lists... Done
Building dependency tree      
Reading state information... Done
E: Couldn't find package 1:5.3p1-3ubuntu3
最後一句話說明，sudo apt-get install此路不通啊，於是換一條路。

在百度上搜索5.3p1-3ubuntu3得到的有用資訊非常少，在google上搜索5.3p1-3ubuntu3發現了一個地址，，網頁方式直接下載了一個對應檔案。”ssh_5.3p1-3ubuntu3_all.deb”
本來我覺得只要安裝它應該就可以了，於是

[email protected]:~/Downloads$ sudo dpkg -i ssh_5.3p1-3ubuntu3_all.deb

但是，讓人吐血的一步來了，

Selecting previously deselected package ssh.
(Reading database ... 127434 files and directories currently installed.)
Unpacking ssh (from ssh_5.3p1-3ubuntu3_all.deb) ...
dpkg: dependency problems prevent configuration of ssh:
 ssh depends on openssh-server; however:
  Package openssh-server is not installed.
dpkg: error processing ssh (--install):
 dependency problems - leaving unconfigured
Errors were encountered while processing: ssh
注意一下，它說 ssh depends on openssh-server; however:Package openssh-server is not installed.也就是說，剛才安裝openssh-server時它說需要openssh-client，現在安裝openssh-client了，它又說需要先裝openssh-server。這樣豈不是死迴圈了。

發現，其實網上說得很明白，我剛才自己沒有看清楚。要成功地裝ssh需要三步。

剩下的事兒就好辦了。下載安裝即可。

下載並安裝第一個檔案

[email protected]:~/Downloads$ sudo dpkg -i openssh-client_5.3p1-3ubuntu3_i386.deb
dpkg: warning: downgrading openssh-client from 1:5.3p1-3ubuntu5 to 1:5.3p1-3ubuntu3.
(Reading database ... 127436 files and directories currently installed.)
Preparing to replace openssh-client 1:5.3p1-3ubuntu5 (using openssh-client_5.3p1-3ubuntu3_i386.deb) ...
Unpacking replacement openssh-client ...
Setting up openssh-client (1:5.3p1-3ubuntu3) ...
Processing triggers for man-db ...

下載並安裝第二個檔案

[email protected]:~/Downloads$ sudo dpkg -i openssh-server_5.3p1-3ubuntu3_i386.deb
Selecting previously deselected package openssh-server.
(Reading database ... 127436 files and directories currently installed.)
Unpacking openssh-server (from openssh-server_5.3p1-3ubuntu3_i386.deb) ...
Setting up openssh-server (1:5.3p1-3ubuntu3) ...
Creating SSH2 RSA key; this may take some time ...
Creating SSH2 DSA key; this may take some time ...
 * Stopping OpenBSD Secure Shell server sshd                                                              [ OK ]
ssh start/running, process 3822
Processing triggers for ureadahead ...
ureadahead will be reprofiled on next reboot
Processing triggers for ufw ...
Processing triggers for man-db ...

下載並安裝第三個檔案

[email protected]:~/Downloads$ sudo dpkg -i ssh_5.3p1-3ubuntu3_all.deb
(Reading database ... 127454 files and directories currently installed.)
Preparing to replace ssh 1:5.3p1-3ubuntu3 (using ssh_5.3p1-3ubuntu3_all.deb) ...
Unpacking replacement ssh ...
Setting up ssh (1:5.3p1-3ubuntu3) ...

最後試了試，成功。

[email protected]:~/Downloads$ ssh localhost
The authenticity of host 'localhost (::1)' can't be established.
RSA key fingerprint is 0f:f5:b7:32:06:a3:3c:4c:de:fb:04:aa:8a:f2:2d:ee.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'localhost' (RSA) to the list of known hosts.