HDFS简介
HDFS即Hadoop Distributed File System，是一个分布式文件系统，用于存储海量数据。一个HDFS集群由一个NameNode和多个DataNode组成。
HDFS特性
- 主从架构
分块存储
副本机制
元数据记录
抽象目录树
HDFS shell命令行
- Hadoop内置提供了shell命令行，格式为hadoop fs 参数。前面hadoop fs为固定搭配，表示操作的是文件系统，具体操作的文件系统则看参数中文件路径url的前缀协议。
示例如下：
[root@node1 ~]# hadoop fs -ls file:///
Found 21 items
-rw-r--r-- 1 root root 0 2021-10-26 14:27 file:///.autorelabel
dr-xr-xr-x - root root 28672 2021-10-26 15:12 file:///bin
dr-xr-xr-x - root root 4096 2020-09-11 14:44 file:///boot
drwxr-xr-x - root root 3260 2022-10-25 19:23 file:///dev
drwxr-xr-x - root root 8192 2022-10-25 19:23 file:///etc
drwxr-xr-x - root root 48 2021-10-26 15:15 file:///export
drwxr-xr-x - root root 6 2018-04-11 12:59 file:///home
dr-xr-xr-x - root root 4096 2020-09-11 14:40 file:///lib
dr-xr-xr-x - root root 24576 2020-09-11 14:40 file:///lib64
drwxr-xr-x - root root 6 2018-04-11 12:59 file:///media
drwxr-xr-x - root root 6 2018-04-11 12:59 file:///mnt
drwxr-xr-x - root root 16 2020-09-11 14:40 file:///opt
dr-xr-xr-x - root root 0 2022-10-25 19:23 file:///proc
dr-xr-x--- - root root 4096 2022-10-24 21:15 file:///root
drwxr-xr-x - root root 840 2022-10-25 19:23 file:///run
dr-xr-xr-x - root root 16384 2021-10-26 15:13 file:///sbin
drwxr-xr-x - root root 6 2018-04-11 12:59 file:///srv
dr-xr-xr-x - root root 0 2022-10-25 19:23 file:///sys
drwxrwxrwt - root root 4096 2022-10-25 19:34 file:///tmp
drwxr-xr-x - root root 155 2020-09-11 14:39 file:///usr
drwxr-xr-x - root root 4096 2020-09-11 14:46 file:///var
[root@node1 ~]# hadoop fs -ls hdfs://node1:8020/
Found 3 items
drwxr-xr-x - root supergroup 0 2022-10-24 21:14 hdfs://node1:8020/itcast
drwx------ - root supergroup 0 2021-10-26 15:20 hdfs://node1:8020/tmp
drwxr-xr-x - root supergroup 0 2021-10-26 15:23 hdfs://node1:8020/user
[root@node1 ~]# hadoop fs -ls /
Found 3 items
drwxr-xr-x - root supergroup 0 2022-10-24 21:14 /itcast
drwx------ - root supergroup 0 2021-10-26 15:20 /tmp
drwxr-xr-x - root supergroup 0 2021-10-26 15:23 /user
[root@node1 ~]# hdfs dfs -ls /
Found 3 items
drwxr-xr-x - root supergroup 0 2022-10-24 21:14 /itcast
drwx------ - root supergroup 0 2021-10-26 15:20 /tmp
drwxr-xr-x - root supergroup 0 2021-10-26 15:23 /user
shell命令行常用操作
HDFS shell命令行的常用操作基本与Linux相同。具体如下：
创建文件夹：hadoop fs -mkdir -p
[root@node1 ~]# hadoop fs -mkdir -p /study/hdfs
[root@node1 ~]# hdfs dfs -ls /
Found 4 items
drwxr-xr-x - root supergroup 0 2022-10-24 21:14 /itcast
drwxr-xr-x - root supergroup 0 2022-10-25 20:11 /study
drwx------ - root supergroup 0 2021-10-26 15:20 /tmp
drwxr-xr-x - root supergroup 0 2021-10-26 15:23 /user
- 显示文件：hadoop fs -ls -h
[root@node1 ~]# hadoop fs -mkdir -p /study/hdfs
[root@node1 ~]# hdfs dfs -ls /
Found 4 items
drwxr-xr-x - root supergroup 0 2022-10-24 21:14 /itcast
drwxr-xr-x - root supergroup 0 2022-10-25 20:11 /study
drwx------ - root supergroup 0 2021-10-26 15:20 /tmp
drwxr-xr-x - root supergroup 0 2021-10-26 15:23 /user
[root@node1 ~]# hadoop fs -put anaconda-ks.cfg /study/hdfs
[root@node1 ~]# hadoop fs -ls /study/hdfs
Found 1 items
-rw-r--r-- 3 root supergroup 1340 2022-10-25 20:14 /study/hdfs/anaconda-ks.cfg
[root@node1 ~]# hadoop fs -ls -h /study/hdfs
Found 1 items
-rw-r--r-- 3 root supergroup 1.3 K 2022-10-25 20:14 /study/hdfs/anaconda-ks.cfg
- 上传文件：hadoop fs -put
[root@node1 ~]# echo 2222 > 2.txt
[root@node1 ~]# hadoop fs -put file:///root/2.txt hdfs://node1:8020/study/hdfs
- 查看文件：hadoop fs -cat
# hadoop fs -cat /itcast/anaconda-ks.cfg
- 下载文件：hadoop fs -get
[root@node1 ~]# ll
总用量 32
-rw-r--r-- 1 root root 2 10月 24 21:15 1.txt
-rw-------. 1 root root 1340 9月 11 2020 anaconda-ks.cfg
drwxr-xr-x 2 root root 55 10月 5 00:08 hivedata
-rw------- 1 root root 23341 10月 5 00:11 nohup.out
[root@node1 ~]# hadoop fs -get hdfs://node1:8020/itcast/2.txt file:///root/
[root@node1 ~]# ll
总用量 36
-rw-r--r-- 1 root root 2 10月 24 21:15 1.txt
-rw-r--r-- 1 root root 5 10月 25 21:08 2.txt
-rw-------. 1 root root 1340 9月 11 2020 anaconda-ks.cfg
drwxr-xr-x 2 root root 55 10月 5 00:08 hivedata
-rw------- 1 root root 23341 10月 5 00:11 nohup.out
[root@node1 ~]# hadoop fs -get /itcast/2.txt ./666.txt
拷贝文件：hadoop fs -cd
追加数据到HDFS文件中：hadoop fs -appendToFile 注意！这个命令需要把集群全部打开，因为它涉及到了datanode节点，具体想了解的话可以看我上一篇博客
[root@node1 ~]# hadoop fs -appendToFile 1.txt 3.txt /2.txt
[root@node1 ~]# hadoop fs -cat /2.txt
2222
1
3
- 数据移动（重命名）：hadoop fs -mv
