Eject USB drives / eject command

Question

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?

Answer 1

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.

Answer 2

On Linux, eject will work, but will not really "finish the job" regarding USB rotating drives.

So first, you eject /dev/sdb (or umount everything).

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

    udisksctl power-off -b /dev/sdb

or

    udisks --detach /dev/sdb

This usually causes the drive to spin down gracefully.

Note: udisksctl might be a more "mainstream" tool, compared to udisks (the former is already installed on my Debian, the latter isn't & has been criticised for unnecessary spin up/down).

Some details

udisksctl

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.

udisks (deprecated?)

Precisely, the current implementation (as of 2014):

• 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.

Answer 3

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.

Answer 4

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.

Answer 5

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 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

Answer 6

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

diskutil eject /Volumes/<LABEL>

Answer 7

"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

Note that /dev/sdc1 has disappeared.

Answer 8

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

Answer 9

Based on two top answers. Just using udisksctl results in error if still mounted and eject alone does not power-off, only unmounts USB. Therefore I wrote simple one-liner to create a function in bash:

 e_ject() { 2>/dev/null eject $1;udisksctl power-off -b $1; }; export -f e_ject

To use:

e_ject /dev/sdX

Even more complex and user friendly:

'e_ject() { dev=$(mount| grep $1 | awk --field-separator " " '{ FS = " " ; print $1 ; exit }');2>/dev/null eject $dev;udisksctl power-off -b $dev; }; export -f e_ject'

To use:

e_ject name

name is searched (grepped) in mount output of all mounts, expected to be present on one line only, but seems to work fine even if on multiple mounts e.g. for e_ject sdb with multiple partitions USB stick. On my system both eject and udisksctl work with partition (/dev/sdbx) parameter.

P.S.

2>/dev/null is added due to eject outputing an error each time, but result seemed correct.

Not sure a function need to be exported each time of login, but count not find an asnwer to that in man bash and do not want to google now. Therefore to be on the safe side below (adding to user profile) is expected to be Ok (multiple re-export did not output any errors):

echo 'e_ject() { 2>/dev/null eject $1;udisksctl power-off -b $1; }; export -f e_ject' >> /home/$(id -u -n)/.profile

Answer 10

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

Answer 11

In gnome,

$ gio mount -e /media/dzmanto/MYUSB

ejects a drive MYUSB. No root privileges are required.