1鸥咖，防火墻沒關(guān)閉燕鸽、或者沒有啟動 yarn 集群中錯誤首先看防火墻。
2啼辣，datanode 不被 namenode 識別問題
Namenode 在 format 初始化的時候會形成兩個標(biāo)識啊研，blockPoolId 和
clusterId。新的datanode 加入時鸥拧，會獲取這兩個標(biāo)識作為自己工作目錄中的
標(biāo)識党远。一旦 namenode 重新 format 后，namenode 的身份標(biāo)識已變富弦，而
datanode 如果依然持有原來的 id沟娱，就不會被 namenode 識別。
解決辦法腕柜，刪除 datanode 節(jié)點(diǎn)中的數(shù)據(jù)后济似，再次重新格式化 namenode柳爽。
3 ，jps 不生效碱屁。
原因：全局變量 hadoop java 沒有生效，需要 source /etc/profile 文件
4蛾找，8088 端口連接不上
$ cat /etc/hosts
注釋掉如下代碼
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 hadoop102
5娩脾，Hadoop集群從節(jié)點(diǎn)出現(xiàn)錯誤： Retrying connect to server:
0.0.0.0/0.0.0.0:8031. Already tried 0 time(s);
6，在使用啟動集群的命令start-dfs.sh時打毛，出現(xiàn)下面的警告：
WARN util.NativeCodeLoader: Unable to load native-hadoop library for your
platform... using builtin-java classes where applicable
或者另一個錯誤：
-c: Unknown cipher type 'cd'
admin1: stopping namenode
try: ssh: Could not resolve hostname try: Name or service not known
disabled: ssh: Could not resolve hostname disabled: Name or service not known
VM: ssh: Could not resolve hostname VM: Name or service not known
will: ssh: Could not resolve hostname will: Name or service not known
recommended: ssh: Could not resolve hostname recommended: Name or service not known
It's: ssh: Could not resolve hostname It's: Name or service not known
HotSpot(TM): ssh: Could not resolve hostname HotSpot(TM): Name or service not known
have: ssh: Could not resolve hostname have: Name or service not known
The: ssh: Could not resolve hostname The: Name or service not known
VM: ssh: Could not resolve hostname VM: Name or service not known
which: ssh: Could not resolve hostname which: Name or service not known
have: ssh: Could not resolve hostname have: Name or service not known
might: ssh: Could not resolve hostname might: Name or service not known
Client: ssh: Could not resolve hostname Client: Name or service not known
the: ssh: Could not resolve hostname the: Name or service not known
highly: ssh: Could not resolve hostname highly: Name or service not known
that: ssh: Could not resolve hostname that: Name or service not known
'execstack: ssh: Could not resolve hostname 'execstack: Name or service not known
stack: ssh: Could not resolve hostname stack: Name or service not known
guard: ssh: Could not resolve hostname guard: Name or service not known
library: ssh: Could not resolve hostname library: Name or service not known
guard.: ssh: Could not resolve hostname guard.: Name or service not known
You: ssh: Could not resolve hostname You: Name or service not known
warning:: ssh: Could not resolve hostname warning:: Name or service not known
loaded: ssh: Could not resolve hostname loaded: Name or service not known
fix: ssh: Could not resolve hostname fix: Name or service not known
it: ssh: Could not resolve hostname it: Name or service not known
to: ssh: Could not resolve hostname to: Name or service not known
stack: ssh: Could not resolve hostname stack: Name or service not known
Java: ssh: Could not resolve hostname Java: Name or service not known
now.: ssh: Could not resolve hostname now.: Name or service not known
library: ssh: Could not resolve hostname library: Name or service not known
the: ssh: Could not resolve hostname the: Name or service not known
you: ssh: Could not resolve hostname you: Name or service not known
fix: ssh: Could not resolve hostname fix: Name or service not known
'-z: ssh: Could not resolve hostname '-z: Name or service not known
or: ssh: Could not resolve hostname or: Name or service not known
with: ssh: Could not resolve hostname with: Name or service not known
<libfile>',: ssh: Could not resolve hostname <libfile>',: Name or service not known
link: ssh: Could not resolve hostname link: Name or service not known
noexecstack'.: ssh: Could not resolve hostname noexecstack'.: Name or service not known
with: ssh: Could not resolve hostname with: Name or service not known
7柿赊，在hadoop集群的master中用命令運(yùn)行例子易出現(xiàn)的故障：
- 錯誤現(xiàn)象：java.lang.OutOfMemoryError: Java heap space.
** 原因：**JVM內(nèi)存不夠。
** 解決方法**：修改mapred-site.xml中mapred.child.java.opts屬性的值幻枉，其默認(rèn)值是-Xmx200m 可根據(jù)需要適當(dāng)增大 該值碰声。
