2021-07-06 10:04:58 +08:00
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# DD 命令说明
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2018-11-27 13:35:53 +08:00
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2020-12-22 10:43:59 +08:00
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## 1.一般使用
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```bash
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# 不固定长度，读到文件结尾自动停止
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2019-10-15 10:47:10 +08:00
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dd if=\<in file name\> of=/dev/\<out file name\> bs=4M status=progress
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2020-12-22 10:43:59 +08:00
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# 指定长度（4Mx1024=4G）
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dd if=\<in file name\> of=/dev/\<out file name\> bs=4M count=1024 status=progress
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```
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## 2.指定 Flag
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```bash
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# iflag 指定 input flag
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# iflag 指定 output flag
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dd iflag=direct,nonblock if=\<in file name\> oflag=direct,nonblock of=/dev/\<out file name\> bs=4M status=progress
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```
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多个 Flag 之间可以用逗号分割，含义如下表。
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2020-12-22 11:02:29 +08:00
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| Flag | Description |
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|-------------|-------------------------------------------------------------------|
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| append | append mode (makes sense only for output; conv=notrunc suggested) |
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| direct | use direct I/O for data |
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| directory | fail unless a directory |
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| dsync | use synchronized I/O for data |
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| sync | likewise, but also for metadata |
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| fullblock | accumulate full blocks of input (iflag only) |
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| nonblock | use non-blocking I/O |
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| noatime | do not update access time |
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| nocache | Request to drop cache. See also oflag=sync |
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| noctty | do not assign controlling terminal from file |
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| nofollow | do not follow symlinks |
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| count_bytes | treat 'count=N' as a byte count (iflag only) |
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| skip_bytes | treat 'skip=N' as a byte count (iflag only) |
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| seek_bytes | treat 'seek=N' as a byte count (oflag only) |
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