当我们打开系统输入hadoop启动命令start-all.sh时出现以下错误：

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[root@master ~]# start-all.sh
starting namenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-namenode-master.out
master: ssh: connect to host master port 22: Network is unreachable
master: ssh: connect to host master port 22: Network is unreachable
starting jobtracker, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-jobtracker-master.out
master: ssh: connect to host master port 22: Network is unreachable

我们查看进程：

[root@master ~]# jps
2739 Jps
[root@master ~]#

显示我们hadoop没有启动。

我的解决方法：

我们先查看我们当前虚拟机系统的ip为192.168.40.128,

[root@master ~]# ifconfig
eth2      Link encap:Ethernet  HWaddr 00:0C:29:4E:BC:7A  
          inet addr:192.168.40.128  Bcast:192.168.40.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe4e:bc7a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:127 errors:0 dropped:0 overruns:0 frame:0
          TX packets:134 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:12497 (12.2 KiB)  TX bytes:14291 (13.9 KiB)
          Interrupt:19 Base address:0x2024 
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:24 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:1616 (1.5 KiB)  TX bytes:1616 (1.5 KiB)

然后我们编辑查看/etc/hosts文件里的配置：

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
192.168.80.100 master#hadoop的ip配置
~                                                                                           
~                                                                                           
~                                                                                                                                                                                 
                                                                                         
"/etc/hosts" 3L, 180C

我们可以看到master,hadoop的ip配置为：192.168.80.100，与当前系统的ip不一致。键盘按i编辑修改ip为当前系统ip（192.168.40.128），按esc输入:wq退出保存。然后重新启动start-all.sh

[root@master ~]# start-all.sh
starting namenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-namenode-master.out
master: Warning: Permanently added the RSA host key for IP address '192.168.40.128' to the list of known hosts.
master: starting datanode, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-datanode-master.out
master: starting secondarynamenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-secondarynamenode-master.out
starting jobtracker, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-jobtracker-master.out
master: starting tasktracker, logging to /usr/local/hadoop/libexec/../logs/hadoop-root-tasktracker-master.out

启动成功，查看进程

[root@master ~]# jps
3065 SecondaryNameNode
3400 Jps
3146 JobTracker
2951 DataNode
2843 NameNode
3260 TaskTracker

成功

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