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补充 DD 参数. 

Signed-off-by: rick.chan <chenyang@autoai.com>
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rick.chan 2020-12-22 10:43:59 +08:00
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Software/Applications/DD/DD_命令的使用.md
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# DD 命令的使用
## 1.一般使用
```bash
# 不固定长度，读到文件结尾自动停止
dd if=\<in file name\> of=/dev/\<out file name\> bs=4M status=progress
# 指定长度（4Mx1024=4G）
dd if=\<in file name\> of=/dev/\<out file name\> bs=4M count=1024 status=progress
```
## 2.指定 Flag
```bash
# iflag 指定 input flag
# iflag 指定 output flag
dd iflag=direct,nonblock if=\<in file name\> oflag=direct,nonblock of=/dev/\<out file name\> bs=4M status=progress
```
多个 Flag 之间可以用逗号分割，含义如下表。
| flags | Description |
|-----------|----------------------------------------------|
| direct | 读写数据采用直接 IO 方式 |
| directory | 读写失败除非是 directory |
| dsync | 读写数据采用同步 IO |
| sync | 同上，但是针对元数据 |
| fullblock | accumulate full blocks of input |
| nonblock | 读写数据采用非阻塞 IO 方式 |
| noatime | 读写数据不更新访问时间 |
| noctty | do not assign controlling terminal from file |
| nofollow | do not follow symlinks |