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vanden
Asked: 2010-07-30 09:04:00 +0800 CST

Why do I need root privileges to umount a drive at the command line, but not in Nautilus? How to change that?

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When I insert a thumb drive, media card, or USB hard drive, to unmount it via the command line, I need to use:

sudo umount /media/the_device

But, I can unmount the device in a file manager like Nautilus simply by clicking the eject button or using the right-click context menu on the device.

What is the rationale for the difference? How can I change it so that I can unmount from the command line without needing root privileges? Is changing it a bad idea?

Edit: In case it has changed, I am running 9.04. I've run most versions 5.10--9.04, and as far as I recall, it has always been this way.

command-line sudo umount

3 Answers

  1. Best Answer

    Nautilus doesn't unmount the device directly; it talks over DBus to a system daemon (udisks-daemon) and asks it to unmount.

    The daemon checks if you're allowed to do that, by contacting another system daemon, PolicyKit.

    PolicyKit uses the configuration defined in /usr/share/polkit-1/actions/org.freedesktop.udisks.policy (unless the local system administrator overrides it in /etc/polkit-1). That file tells PolicyKit that users with active console sessions can detatch drives, so PolicyKit talks to a third daemon, ConsoleKit, to see if you have active console sessions. Logging in via gdm counts as a console session; logging in via ssh doesn't.

    There's a command-line tool udisks that lets you unmount devices without using sudo, using the same mechanism:

    udisks --unmount /dev/sdb1

    that unmounts the filesystem; I can also detatch the whole device with

    udisks --detach /dev/sdb

    which makes the LED on my USB key go dark.

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  2. The situation might have changed -- in current Ubuntu 10.04 umount works without sudo for USB drives. Generally I think that the command 

    gvfs-mount -u /media/the_device

    (gvfs-mount is in the gvfs-bin package) should always work.

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  3. Current answers are deprecated. Try with GIO command line tool.

    gio mount --unmount *mounted location*

    Get the current mounted partitions with, for example:

    lsblk | grep media

    Reference

    Gio is a GTK library providing useful classes for general purpose I/O, networking, IPC, settings, and other high level application functionality.

    GIO provides a portable, modern and easy-to-use file system abstraction API for accessing local and remote files; a set of low and high level abstractions over the DBus IPC specification; an application settings API; portable networking abstractions; and additional utilities for writing asynchronous operations without blocking the user interface of your application.

    gio mount

    Provides commandline access to various aspects of GIO’s mounting functionality.

    Mounting refers to the traditional concept of arranging multiple file systems and devices in a single tree, rooted at /. Classical mounting happens in the kernel and is controlled by the mount utility. GIO expands this concept by introducing mount daemons that can make file systems available to GIO applications without kernel involvement.

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