离线镜像查看器用于查看HDFS镜像。hadoop2.4之前的镜像查看器与之后的不同，要查看2.4之前的，请用2.3的查看器，或者用oiv_legacy Command 命令。
输出格式：
1)web http(默认方式)
2)XML
使用方式：
1)web方式
首先启动HTTP REST:
列出有哪些目录:
查看指定目录:
2)XML方式
将fsimage里的内容dump到xml中
命令选项:
| Flag | Description |
| -i|--inputFile input file | Specify the input fsimage file to process. Required. |
| -o|--outputFile output file | Specify the output filename, if the specified output processor generates one. If the specified file already exists, it is silently overwritten. (output to stdout by default) |
| -p|--processor processor | Specify the image processor to apply against the image file. Currently valid options are Web (default), XML and FileDistribution. |
| -addr address | Specify the address(host:port) to listen. (localhost:5978 by default). This option is used with Web processor. |
| -maxSize size | Specify the range [0, maxSize] of file sizes to be analyzed in bytes (128GB by default). This option is used with FileDistribution processor. |
| -step size | Specify the granularity of the distribution in bytes (2MB by default). This option is used with FileDistribution processor. |
| -h|--help | Display the tool usage and help information and exit. |