一、启动namenode服务后，web页面依然无法访问
1、启动namenode服务，
指令：start-all.sh
'''
[root@hadoop1 hadoop-3.2.1]# start-all.sh
Starting namenodes on [hadoop1]
Starting datanodes
Starting secondary namenodes [hadoop1]
Starting resourcemanager
Starting nodemanagers
ERROR: Refusing to run as root: roo account is not found. Aborting.
'''
2、查看namenode服务是否启动，
'''
[root@hadoop1 hadoop-3.2.1]# jps
8130 Jps
7494 ResourceManager
6871 NameNode
7244 SecondaryNameNode
'''
3、查看后台监听端口
'''
[root@hadoop1 hadoop-3.2.1]# netstat -nltp |grep 6871
tcp 0 0 192.168.43.250:9000 0.0.0.0:* LISTEN 6871/java
tcp 0 0 0.0.0.0:9870 0.0.0.0:* LISTEN 6871/java
'''
4、查看web是否可以访问，发现web页面无法访问
5、检查防火墙设置，可以看到hadoop1服务器已经禁用了除本机外的其他多有服务访问，
[root@hadoop1 hadoop-3.2.1]# service iptables status
表格：filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
2 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
3 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
4 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
5 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
1 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
6、关闭防火墙，并把防火墙设置为开启不启动
centos6：
关闭防火墙：service iptables stop
设置开启不启动防火墙：chkconfig iptables off
centos7：
关闭防火墙：systemctl stop firewalld.service
设置开启不启动防火墙：systemctl disable firewalld.service
7、检查web已经可以正常显示
8、如果上面的操作依然无法访问的话，需要查看一下主机的hosts文件 是否有配置域名映射
二、开启datanode指令时出现waring
[root@hadoop1 hadoop-3.2.1]# hadoop-daemon.sh start datanode
WARNING: Use of this script to start HDFS daemons is deprecated.
WARNING: Attempting to execute replacement "hdfs --daemon start" instead.
主要是2.7版本的hadoop已经把hadoop命令改为hdfs命令了，所以尝试使用
指令：hdfs --daemon start datanode
'''
[root@hadoop2 hadoop-3.2.1]# hdfs --daemon start datanode
[root@hadoop2 hadoop-3.2.1]# jps
4064 Jps
4033 DataNode
2922 ResourceManager
'''
三、使用root配置的hadoop并启动会出现报错
错误：
Starting namenodes on [master]
ERROR: Attempting to operate on hdfs namenode as root
ERROR: but there is no HDFS_NAMENODE_USER defined. Aborting operation.
Starting datanodes
ERROR: Attempting to operate on hdfs datanode as root
ERROR: but there is no HDFS_DATANODE_USER defined. Aborting operation.
Starting secondary namenodes [slave1]
ERROR: Attempting to operate on hdfs secondarynamenode as root
ERROR: but there is no HDFS_SECONDARYNAMENODE_USER defined. Aborting operation.
原因分析：由于root没有start-dfs.sh和 stop-dfs.sh脚本的执行权限，在这两个脚本的开头加上如下参数，给root赋予执行权限即可：
HDFS_DATANODE_USER=root
HADOOP_SECURE_DN_USER=hdfs /* 后续版本这边需要修改为 HDFS_DATANODE_SECURE_USER=hdfs
HDFS_NAMENODE_USER=root
HDFS_SECONDARYNAMENODE_USER=root
start-yarn.sh，stop-yarn.sh顶部也需添加以下
YARN_RESOURCEMANAGER_USER=root
HADOOP_SECURE_DN_USER=yarn /* 后续版本这边需要修改为 HDFS_DATANODE_SECURE_USER=hdfs
YARN_NODEMANAGER_USER=root
4、hdfs运行指令时出现warn警告提示：
2019-11-13 00:07:58,517 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
该警告信息主要是由于是依赖库的问题
我们对静态库查看下依赖：看下依赖是否都正常：
通过指令 ldd libhadoop.so.1.0.0
'''
./libhadoop.so.1.0.0: /lib64/libc.so.6: version `GLIBC_2.14' not found (required by ./libhadoop.so.1.0.0)
linux-vdso.so.1 => (0x00007fff369ff000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f3caa7ea000)
libc.so.6 => /lib64/libc.so.6 (0x00007f3caa455000)
/lib64/ld-linux-x86-64.so.2 (0x00007f3caac1b000)
'''
可以看到是glibc 版本的问题：
我们再确认下：
GLIBC_2.14找不到，现在检查系统的glibc库, ldd --version 即可检查。
输入命令：
'''
ldd --version
ldd (GNU libc) 2.12
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.
'''
还可以直接确认下glibc 目前支持的版本：
通过如下查询方法：
'''
strings /lib64/libc.so.6|grep GLIBC
GLIBC_2.2.5
GLIBC_2.2.6
GLIBC_2.3
GLIBC_2.3.2
GLIBC_2.3.3
GLIBC_2.3.4
GLIBC_2.4
GLIBC_2.5
GLIBC_2.6
GLIBC_2.7
GLIBC_2.8
GLIBC_2.9
GLIBC_2.10
GLIBC_2.11
GLIBC_2.12
GLIBC_PRIVATE
'''
可以看到目前只支持到 2.12
解决办法有两个
1、升级 glibc 库
2、屏蔽hadoop提示这个告警
直接在log4j日志中去除告警信息。在$HADOOP_HOME/etc/hadoop/log4j.properties文件中添加
log4j.logger.org.apache.hadoop.util.NativeCodeLoader=ERROR