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1) I would like to copy a single file from Ubuntu 18.04's ext4-formatted partition to Window 10's NTFS-formatted partition without going through an intermediate FAT32 partition. Can the "dd" command in Ubuntu do that? What "mount" commands might be needed to do that?

2) If the source is a block of bytes rather than a file, can "dd" transfer those bytes to a file format in the NTFS-formatted partition? (I'm trying to set up the "\linux.bin" file with Window's BCDedit to dual-boot to Ubuntu, as in: bcdedit /set {long id here} path C:\linux.bin where dd's if= is a sector of 512 bytes.)

TimDaniels

TimDaniels
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1 Answers1

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1) I would like to copy a single file from Ubuntu 18.04's ext4-formatted partition to Window 10's NTFS-formatted partition without going through an intermediate FAT32 partition. Can the "dd" command in Ubuntu do that? What "mount" commands might be needed to do that?

dd does not care about partitions or filesystems. Its input and output are ordinary files, and the only thing it does is copy data, byte-by-byte (or chunk-by-chunk) from its input to its output.

In your situation, dd isn't any more useful than regular cp or even cat. After you have mounted both the source ext4 partition and the destination NTFS partition on Linux, you can just... copy the files using cp or other regular tools or even using a graphical file manager.

To mount an NTFS filesystem with read/write features, install ntfs-3g. No special options are needed from the Linux side (generally), but if this is an internal disk, you do need to make sure Windows has fully unmounted it during shutdown – i.e. hasn't gone into 'hibernate' or 'hybrid' or 'fast startup' mode.

(For example, you can use shutdown /s /t 0 from Windows in order to begin a full shutdown.)

2) If the source is a block of bytes rather than a file, can "dd" transfer those bytes to a file format in the NTFS-formatted partition? (I'm trying to set up the "\linux.bin" file with Window's BCDedit to dual-boot to Ubuntu, as in: bcdedit /set {long id here} path C:\linux.bin where dd's if= is a sector of 512 bytes.)

Same answer as before. dd does not understand filesystems; it just copies files. So if the output needs to be a file on NTFS, you must mount the NTFS filesystem within Linux itself, and then dd will simply write to the file you give it.

So just mount the NTFS partition like you did in part 1 above, and use dd if=/dev/xxx of=/mnt/windows/linux.bin bs=... count=... to copy the bootcode.

The sector size is irrelevant to the final data. It only tells dd how large a chunk to read at once – e.g. reading a single 512-byte chunk is much faster than reading 512 one-byte chunks, but the resulting data will be identical either way.

(That is, dd if=A of=B bs=1 count=512 and dd if=A of=B bs=512 count=1 will create identical files, just doing it at different speeds.

In fact, head -c 512 A > B will create an identical file to both.)

u1686_grawity
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    Upvoted, one problem though: while specifying count you may not get identical files. You will be surprised if dd reads a partial input block. This will still count as a successful read but it will provide less than ibs data. In effect, when you reach count you will not reach the amount of data you wanted. I have never seen this while reading from a local filesystem, but in general (pipes, named pipes, network mounts?, FUSE?) you need iflag=fullblock. Proof of concept: </dev/zero dd bs=1 | dd bs=4M count=2 | wc -c. – Kamil Maciorowski Nov 19 '18 at 06:39
  • Apparently dd does not need a source to be a named file, but it also can take just a block of hex code from a physical location identified only by its sector no. and write it into a file of a format that corresponds to the destination file system, adding metadata and record structure in the process. True? False? – TimDaniels Nov 19 '18 at 09:10
  • Is ntfs-3g included as part of Ubuntu 18.04 or must it be downloaded from an online repository? Once ntfs-3g is installed and the proper "mount" commands executed, then, dd can copy the MBR, known only by its location at the beginning of disc, or a partition boot record known only by its location at the beginning of the partition, directly to a file in an NTFS partition (such as Windows) without using an intermediary shared FAT32 partition? – TimDaniels Nov 19 '18 at 09:22
  • @TimDaniels: It is part of the core repositories, although I'm not sure whether it is part of the "base" installation. Is there some other reason, besides ntfs-3g support, that you're asking whether an intermediary partition would be needed? – u1686_grawity Nov 19 '18 at 10:54
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    @TimDaniels: The source in dd if=…, as well as the destination, is always a named file. It might be a virtual "device" file provided by the kernel, but as far as dd knows, it's still just a file. dd never adds any metadata. dd never adds any record structure. dd does not understand filesystems. The only way to make dd create a file on NTFS is to mount the NTFS filesystem globally. – u1686_grawity Nov 19 '18 at 10:56
  • @grawity: I'm trying to launch Linux's Grub2 boot manager from Windows 10's BCD by providing a copy of the SSD device's MBR to Windows' BCD in the form of a path to an NTFS file containing that MBR copy. Usually, one uses dd to copy the MBR to a shared partition with Linux, then copy the resulting file to Window's partition with Windows, and provide a path to that file to Windows' BCD for the Windows' boot manager to use to boot Linux. I would like to not need the intermediary file and to dd directly to the Windows NTFS file system. – TimDaniels Nov 22 '18 at 04:13