官方文档：https://hadoop.apache.org/docs/r3.1.2/
hadoop fs -ls / 看根目录下的所有文件
hdfs dfs -put alice.txt 上传
hdfs dfs -get /hdfsPath /localPath 下载到本地
hdfs dfsadmin -report.
Edits + Fsimage过程在 hdfs-site.xml 中指定路径。
启动服务时可能会删除一些文件：sudo rm -r /usr/local/hadoop_store/hdfs/datanode/current
current文件夹下对应的文件：
1. Fsimage文件：HDFS文件系统元数据的一个永久性的检查点，其中包含HDFS文件系统的所有目录和文件idnode的序列化信息；
2. Fsimage.md5文件：是镜像文件的 md5 校验文件，这个校验文件是为了判断镜像文件是否被修改；
3. Edits文件：存放HDFS文件系统的所有更新操作，文件系统客户端执行的所有写操作首先会被记录到Edits文件中。
4. seen_txid文件：它代表的是 namenode 里面的 edits_* 文件的尾数，namenode 重启的时候，会按照 seen_txid 的数字， 循序从头跑 edits_0000001~ 到 seen_txid 的数字。
5. VERSION文件：记录了当前NameNode的一些信息。
显示HDFS块信息
hadoop@node-master:~$ hdfs fsck / -files Connecting to namenode via http://node-master:9870/fsck?ugi=hadoop&files=1&path=%2F FSCK started by hadoop (auth:SIMPLE) from /192.168.56.2 for path / at Sun Oct 27 17:37:28 AEDT 2019 / <dir> /alice.txt 173595 bytes, replicated: replication=2, 1 block(s): OK /readme.txt 152 bytes, replicated: replication=2, 1 block(s): OK Status: HEALTHY Number of data-nodes: 3 Number of racks: 1 Total dirs: 1 Total symlinks: 0 Replicated Blocks: Total size: 173747 B Total files: 2 Total blocks (validated): 2 (avg. block size 86873 B) Minimally replicated blocks: 2 (100.0 %) Over-replicated blocks: 0 (0.0 %) Under-replicated blocks: 0 (0.0 %) Mis-replicated blocks: 0 (0.0 %) Default replication factor: 2 Average block replication: 2.0 Missing blocks: 0 Corrupt blocks: 0 Missing replicas: 0 (0.0 %) Erasure Coded Block Groups: Total size: 0 B Total files: 0 Total block groups (validated): 0 Minimally erasure-coded block groups: 0 Over-erasure-coded block groups: 0 Under-erasure-coded block groups: 0 Unsatisfactory placement block groups: 0 Average block group size: 0.0 Missing block groups: 0 Corrupt block groups: 0 Missing internal blocks: 0 FSCK ended at Sun Oct 27 17:37:28 AEDT 2019 in 3 milliseconds The filesystem under path '/' is HEALTHY
hadoop@node-master:~$ hdfs fsck / -blocks Connecting to namenode via http://node-master:9870/fsck?ugi=hadoop&blocks=1&path=%2F FSCK started by hadoop (auth:SIMPLE) from /192.168.56.2 for path / at Sun Oct 27 17:40:29 AEDT 2019 Status: HEALTHY Number of data-nodes: 3 Number of racks: 1 Total dirs: 1 Total symlinks: 0 Replicated Blocks: Total size: 173747 B Total files: 2 Total blocks (validated): 2 (avg. block size 86873 B) Minimally replicated blocks: 2 (100.0 %) Over-replicated blocks: 0 (0.0 %) Under-replicated blocks: 0 (0.0 %) Mis-replicated blocks: 0 (0.0 %) Default replication factor: 2 Average block replication: 2.0 Missing blocks: 0 Corrupt blocks: 0 Missing replicas: 0 (0.0 %) Erasure Coded Block Groups: Total size: 0 B Total files: 0 Total block groups (validated): 0 Minimally erasure-coded block groups: 0 Over-erasure-coded block groups: 0 Under-erasure-coded block groups: 0 Unsatisfactory placement block groups: 0 Average block group size: 0.0 Missing block groups: 0 Corrupt block groups: 0 Missing internal blocks: 0 FSCK ended at Sun Oct 27 17:40:29 AEDT 2019 in 4 milliseconds The filesystem under path '/' is HEALTHY
hadoop@node-master:~$ hdfs fsck /readme.txt -files Connecting to namenode via http://node-master:9870/fsck?ugi=hadoop&files=1&path=%2Freadme.txt FSCK started by hadoop (auth:SIMPLE) from /192.168.56.2 for path /readme.txt at Sun Oct 27 17:43:58 AEDT 2019 /readme.txt 152 bytes, replicated: replication=2, 1 block(s): OK Status: HEALTHY Number of data-nodes: 3 Number of racks: 1 Total dirs: 0 Total symlinks: 0 Replicated Blocks: Total size: 152 B Total files: 1 Total blocks (validated): 1 (avg. block size 152 B) Minimally replicated blocks: 1 (100.0 %) Over-replicated blocks: 0 (0.0 %) Under-replicated blocks: 0 (0.0 %) Mis-replicated blocks: 0 (0.0 %) Default replication factor: 2 Average block replication: 2.0 Missing blocks: 0 Corrupt blocks: 0 Missing replicas: 0 (0.0 %) Erasure Coded Block Groups: Total size: 0 B Total files: 0 Total block groups (validated): 0 Minimally erasure-coded block groups: 0 Over-erasure-coded block groups: 0 Under-erasure-coded block groups: 0 Unsatisfactory placement block groups: 0 Average block group size: 0.0 Missing block groups: 0 Corrupt block groups: 0 Missing internal blocks: 0 FSCK ended at Sun Oct 27 17:43:58 AEDT 2019 in 1 milliseconds The filesystem under path '/readme.txt' is HEALTHY