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This question already has an answer here:

Is umount $mountpoint always enough to safely remove a single-partition USB drive on a modern GNU/Linux system? Or should I use sync && umount $mountpoint && sync, or perhaps umount $mountpoint && udisks --detach $device? I'd like to use the safest way possible, but on the other hand I don't want to introduce superfluous dependencies or delays into my program.

EDIT: Does umount calls sync to complete any pending writes indeed answers a part of this question (whether sync && umount $mountpoint && sync provides any benefit over umount $mountpoint), but not the whole question (whether udisks --detach $device or some other command provides improved safety), so it's not an exact duplicate.

marked as duplicate by Wouter Verhelst, Satō Katsura, Jeff Schaller, Gilles linux Mar 27 '17 at 23:36

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    SHort answer: umount is safe and doesn't need anything else, but of course, you have to check its return value to see if the command was effective. – xhienne Mar 27 '17 at 16:05
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    Unmounting a USB drive only partially makes it safe to remove. It stops I/O to the filesystem, but it doesn't power down the device, making it possible to remount the device. It also doesn't flush any I/O cache to the device, so the data you think may be on the device, may not be. In a gui, you'll often see an option to "Safely Remove" a USB device. That option sync's first, then unmounts, then powers down the device. – Tim Kennedy Mar 28 '17 at 14:23
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eject will work, but will not really "finish the job" regarding USB rotating drives.

The best way to unplug a USB external hard-drive, after proper unmounting, is:

udisks --detach /dev/sdb

https://unix.stackexchange.com/a/129282/29483

EDIT: Also, as g.rocket points out, this command may be equivalent:

udisksctl power-off -b /dev/sdb
  • Does executing this command after unmounting improve protection against data loss/corruption or only reduce power usage? – Pkkm Mar 27 '17 at 18:35
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    You'd hope it never makes a difference, but I don't know. It does help in the sense that a spinning drive is more vulnerable (docs on mine say "don't move it"), & with a short thick cable it is very hard to unplug without also moving the drive around a bit. – sourcejedi Mar 28 '17 at 7:49

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