I know that the
eject command can be used to eject almost any hardware component attached, but can it be used to eject USB drives?
Is it possible to eject USB drives and external HDD's with the
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Yes. For example:
sudo eject /dev/sda
Other answers here that indicate that you require mechanical ejection hardware are incorrect.
Unmounting is not the same thing as ejecting.
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:
udisksctl power-off -b /dev/sdb
udisks --detach /dev/sdb
This usually causes the drive to spin down gracefully.
udisksctl might be a more "mainstream" tool, compared to
udisks (the former is already installed on my Debian, the latter isn't).
The documentation states (about the power-off option):
Arranges for the drive to be safely removed and powered off. On the OS side this includes ensuring that no process is using the drive, then requesting that in-flight buffers and caches are committed to stable storage. The exact steps for powering off the drive depends on the drive itself and the interconnect used. For drives connected through USB, the effect is that the USB device will be deconfigured followed by disabling the upstream hub port it is connected to.
Note that as some physical devices contain multiple drives (for example 4-in-1 flash card reader USB devices) powering off one drive may affect other drives. As such there are not a lot of guarantees associated with performing this action. Usually the effect is that the drive disappears as if it was unplugged.
Precisely, the current implementation (as of 2014):
If you carefully read eject(1) man page you can see that there are 4 methods of ejecting:
-r This option specifies that the drive should be ejected using a CDROM eject command. -s This option specifies that the drive should be ejected using SCSI commands. -f This option specifies that the drive should be ejected using a remov‐ able floppy disk eject command. -q This option specifies that the drive should be ejected using a tape drive offline command.
When you call eject on HDD/SCSI it issue
ioctl(fd, SG_IO, (void *)&io_hdr); command (copy from
This is equivalent as you safely remove device in MS Windows or MaxOSX.
For some devices this have special mean. For example Kindle 3 after eject command has being moved to charging mode and allow browsing on device, while before screen was locked.
Another utilities do same thing, like this
scsi-spin --force --down /dev/sda
"Ejecting" has no meaning for hardware without a tray or other loading mechanism (I assume it works with tape drives too).
However, testing with an external USB flash drive tells that
eject works much like
umount - with the side effect of making the device nodes disappear, e.g.
% ls /dev/sdc* /dev/sdc /dev/sdc1 % sudo eject /dev/sdc % ls /dev/sdc* /dev/sdc
/dev/sdc1 has disappeared.
In osx command line you should use diskutil where LABEL is label of your usb drive.
diskutil eject /Volumes/<LABEL>
OK i will try to explain this better:
udisks command completely remove and power off any usb device mounted or attached in the system unmount command just unmount the partition ie: dev/sdb1 or whatever but the usb is still present in the system.
So is not the same unmount, eject and detach
udisks = power off the usb
umount = just unmount the partition not the whole pendrive
eject = the same or very close to umount command