Using Gnome-Volume-Manager

GNU/Linux Desktop Survival Guide
by Graham Williams

Using Gnome-Volume-Manager

The gnome-volume-manager will automatically mount removable devices as they are connected. It is run as part of the default Debian session, but will also be started, if needed, if you enter the Removable Storage application under Desktop Preferences in the Applications menu. Otherwise it will need to be run in your session (add gnome-volume-manager to Application $\rightarrow$ Advanced $\rightarrow$ Session). The users need to be in group plugdev.

Note that this works best when you run a single X-session at a time (which is the common scenario). If you have two or more users with concurrent X-sessions on different tty's the permissions become an issue. In this situation it is perhaps best to use the Disk Mounter applets to do the mounting.

If you prefer to give gnome-volume-manager a try in the situation with concurrent users with different X sessions on the one console, and for trusted users (those in plugdev), you could use the following /etc/fstab entry:

/dev/usbkey /media/usbkey auto users,gid=plugdev,umask=0002,defaults

The main points here are the use of users to allow any user to unmount the device, and when mounting the device the gid (group ID) is set to plugdev. The umask then allows group access but not others.

Some background on pmount which is the basis of gnome-volume-manager might be give some insights. The use of pmount is hard coded in the gnome-volume-manager:

$ strings /usr/bin/gnome-volume-manager | grep pmount /usr/bin/pmount-hal %h
Thus there is no reconfigurability here. Also pmount's policy is hard-coded and so can not be configured. Part of pmount's policy is that you need to be able to run pmount in order to mount a device, and so you need to be in the plugdev group to mount a device. An entry in /etc/fstab overrides pmount's policy.
In order to be able to umount a device, pmount requires that this device has been mounted by the user. This is enforced by checking /etc/mtab and parsing the mount options looking for "uid=n". n needs to be the uid of the user trying to unmount the device.
The core issues seem to be that pmount's policy is that if you can run pmount and fulfill certain criteria, you can mount a device. And pumount's policy is that if you are the user who mounted the device and fulfill certain criteria, you can unmount the device.
The problem with g-v-m is that if you have two g-v-m's running, both will get messages from HAL which means that they will race for mounting the device. Ideally one of them should go to sleep even though that solution may not be so satisfactory.

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