前面有篇博文已經介紹了HA得原理，這篇主要來介紹HA的實操，HA原理： https://blog.csdn.net/czz1141979570/article/details/104856251
NN切換：
切換前的正常狀態爲：hadoop101：active hadoop102：standby
現在使用命令kill -9進行人工干預：
test成功，再重新將hadoop101上nn啓動
haadmin getServiceState：
言外之意就是獲取serviceid狀態，
[hadoop@hadoop101 sbin]$ hdfs haadmin -getServiceState nn1
20/03/19 19:16:04 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
standby[hadoop@hadoop102 ~]$ hdfs haadmin -getServiceState nn2
20/03/19 19:25:50 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
active當然，也可以在同一臺機器上查看所有NN節點的工作狀態
這個參數主要是用來爲後期寫shell腳本監控NN1和NN2的運行狀態，後面會專門寫篇博文介紹。
hdfs getconf(get config values from configuration):
言外之意便是根據指定的key可以獲取相應的value，而且是從當前運行的集羣xml配置文件中動態獲取，這個參數也是主要用來監控，後面再介紹，先看下如何使用
[hadoop@hadoop101 sbin]$ hdfs getconf
20/03/19 19:31:13 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
hdfs getconf is utility for getting configuration information from the config file.hadoop getconf
[-namenodes] gets list of namenodes in the cluster.
[-secondaryNameNodes] gets list of secondary namenodes in the cluster.
[-backupNodes] gets list of backup nodes in the cluster.
[-includeFile] gets the include file path that defines the datanodes that can join the cluster.
[-excludeFile] gets the exclude file path that defines the datanodes that need to decommissioned.
[-nnRpcAddresses] gets the namenode rpc addresses
[-confKey [key]] gets a specific key from the configuration
For Example:
[hadoop@hadoop101 sbin]$ hdfs getconf -confKey dfs.nameservices
20/03/19 19:33:32 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
liuyi
[hadoop@hadoop101 sbin]$ hdfs getconf -confKey dfs.blocksize
20/03/19 19:33:47 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
134217728
hdfs fsck：
在HDFS中，提供了fsck命令，用於檢查HDFS上文件和目錄的健康狀態、獲取文件的block塊信息和位置信息等。
具體命令介紹：
-move: 移動損壞的文件到/lost+found目錄下
-delete: 刪除損壞的文件 注意：慎用！
-openforwrite: 輸出檢測中的正在被寫的文件
-list-corruptfileblocks: 輸出損壞的塊及其所屬的文件
-files: 輸出正在被檢測的文件
-blocks: 輸出block的詳細報告 （需要和-files參數一起使用）
-locations: 輸出block的位置信息 （需要和-files參數一起使用）
-racks: 輸出文件塊位置所在的機架信息（需要和-files參數一起使用）
例如要查看HDFS中某個文件的block塊的具體分佈，可以這樣寫：
hadoop fsck /your_file_path -files -blocks -locations -racks
for example:
[hadoop@hadoop101 sbin]$ hdfs fsck /
Connecting to namenode via http://hadoop102:50070/fsck?ugi=hadoop&path=%2F
FSCK started by hadoop (auth:SIMPLE) from /192.168.1.101 for path / at Thu Mar 19 19:59:42 CST 2020
Status: HEALTHY
Total size: 0 B
Total dirs: 7
Total files: 0
Total symlinks: 0
Total blocks (validated): 0
Minimally replicated blocks: 0
Over-replicated blocks: 0
Under-replicated blocks: 0
Mis-replicated blocks: 0
Default replication factor: 3
Average block replication: 0.0
Corrupt blocks: 0
Missing replicas: 0
Number of data-nodes: 2
Number of racks: 1
FSCK ended at Thu Mar 19 19:59:42 CST 2020 in 3 milliseconds主要關注標紅部分。
這裏只簡單介紹下，後面會有fsck故障恢復重演博文。
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