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 eject command?

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    Related: the opposite of eject /dev/sdX is sg_start -s /dev/sdX (from sg3_utils package), both use SCSI commands to send to the device. – Yeti Feb 9 '18 at 12:09

No. Nor do they need to be; eject is used for opening optical drives, where one cannot pull the media from directly.

Unmounting is sufficient for USB/eSATA/etc. storage devices.

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  • Hmm, I saw eject hdd as in /dev/sda somewhere. I guess the reference was wrong then. – Joe Barr Apr 2 '12 at 0:49
  • You can do it, but it usually doesn't do very much if anything at all. – Ignacio Vazquez-Abrams Apr 2 '12 at 0:51
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    This assumes that the device is mounted in the first place, and that carries along another big set of assumptions (it's got a filesystem that you can read, for one). Imagine that you're erasing a bunch of external drives - they probably never get mounted. eject is the right thing to use. – James Moore Oct 5 '12 at 15:03
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    If I'm ever unsure, I sync before yanking it out – EkriirkE May 14 '14 at 6:51
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    Big, fat WARNING: This is NOT completely true. If you do not eject it underlying USB Device Driver may still (try to) write AFTER umount has returned. This can be clearly seen if drive has a status LED. Yanking the USB stick right after umount terminates is RECIPE FOR DISASTER. – ZioByte Sep 11 '19 at 9:49

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.

  1. If you unmount a volume, you can immediately mount it back, because the underlying device is still available. In some situations, this could present a security risk. By ejecting the device, only a reset of the USB subsystem (e.g. a reboot) will reload the device.
  2. By ejecting the device, you effectively disable any further access to the device. Only a reset of the USB subsystem (e.g. a reboot) will reload the device. Otherwise, you must physically disconnect the USB device and reconnect it in order to access it again.
  3. Before ejecting, this command will unmount all volumes on the device that were mounted.
  4. If volumes are in use, this command will fail as with unmount, except that some volumes might be unmounted and some volumes might remain mounted.
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    I also had to use sudo to get this command to finish (all it would do was unmount the drive before saying it was unable to open the file). Other than that, helpful answer. – GDP2 Jan 31 '16 at 5:16
  • Under-appreciated answer in this thread. Just look at a FAT32 mounted thumb drive, and notice how unmounting and ejecting have a world of difference just in the file explorer (ie: nautilus) alone. A simple Sansa clip would also help demonstrate this. – Cloud Sep 21 '16 at 5:17
  • The device is still present when executing lsusb. So you don't have to reset the whole USB-Subsystem. Just the device is sufficient. You can use usbreset to do this github.com/jkulesza/usbreset github.com/CWempe/usbreset The usbreset.c files are identically in both projects, – Hannes Jun 15 '19 at 7:17
  • How do I know that "sda" is the right one? Can I map sda, sdb, etc to the real device names? – Jürgen K. Oct 31 '19 at 13:29
  • you can use blkid as in sudo blkid /dev/sda1 to get the label of your usb drive, if it has one. Otherwise you can always revert to the dumb way, which is to check the size of drives listed with sudo lsblk. Of course this assumes you know the drive's size, and it differs significantly from other devices... – Romain Vincent May 17 at 1:19

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

This usually causes the drive to spin down gracefully.

Precisely, the current implementation:

  • sends SCSI sync-cache command,
  • sends SCSI stop command,
  • unbinds the usb-storage kernel driver,
  • suspends the USB device (power),
  • logically disables/removes it from its USB port.

This process is close to the manual procedure that is suggested here. Initial answer was on askubuntu.

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

udisksctl power-off -b /dev/sdb
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  • On my ubuntu onyl udisksctl which does not have --detach otion is available. What to do in this case? thank you. – Wakan Tanka Jan 11 '16 at 14:37
  • @WakanTanka you install udisks. – Totor Jan 20 '16 at 0:37
  • How can I install udisks? It is not on my system. I found the package udisks2, but that did not make udisks or udisks2 available. – Martin Thoma May 14 '16 at 8:07
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    @WakanTanka udisksctl power-off -b /dev/sdwhatever seems to do the same thing. – Gavin S. Yancey Sep 30 '16 at 3:38
  • @g.rocket answer updated accordingly. Thank you. – Totor Sep 30 '16 at 19:22

Manual steps for unmounting disk /dev/sdb (Requires sudo):

echo 'offline' > /sys/block/sdb/device/state
echo '1' > /sys/block/sdb/device/delete

This will completely power-off the device and detach it from the system. It won't be detected again till it is disconnected and re-attached.

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    FWIW this is the only thing that works for me in a Xen dom0 with an external USB cradle - the eject and udisks commands gave errors. – GS - Apologise to Monica Jan 13 '18 at 10:19
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    I was searching for this, i'm in dracut emergency mode and I don't have access to any of the other functions. Thanks! – Nassiel Oct 25 '18 at 12:03
  • hdparm -Y is also handy for SATA/IDE drives. – Walf Feb 1 '19 at 6:39

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

   -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 eject.c sources).

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
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"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*

Note that /dev/sdc1 has disappeared.

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    Never tried it with tapes (mt rewoffl is more convenient because it also rewinds), but it does work with motorised floppy drives like those found on old Macs and Sun workstations. – Alexios Apr 2 '12 at 4:23
  • @Alexios interesting. – Renan Apr 2 '12 at 16:14

In osx command line you should use diskutil where LABEL is label of your usb drive.

diskutil eject /Volumes/<LABEL>
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udisks --detach /dev/sdX where (X) is the last letter of your usb device. It works fine on any linux system.

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  • Your answer is okay, although maybe it is a little bit short. I would suggest to elaborate more: what this command does, how, why is this what you suggest, etc. – peterh - Reinstate Monica Oct 4 '15 at 3:25

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

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