Fedora Linux

Figure 2-32. Removable Drives and Media Preferences tool

The first tab, Storage, contains four checkboxes for USB storage devices:

Mount removable drives when hot-plugged

Freshly inserted USB drives will be mounted, and a corresponding icon will appear on the desktop.

Mount removable media when inserted

Freshly inserted media such as CDs and DVDs will be mounted, and an icon will appear on the desktop.

This option does not apply to media inserted into a memory-card reader! Use the 'Mount removable drives when hot-plugged' option for memory cards. 

Browse removable media when inserted

Removable drives and removable media will be displayed in a Nautilus window when they are mounted, regardless of whether they are mounted automatically (depending on the settings of the checkboxes) or manually.

Auto-run programs on new drives and media

Searches for a file named autorun on newly mounted media, prompts the user for confirmation, and then executes that file. The file may be a script or a compiled program.

The auto-run feature does not work with automatically mounted media because GNOME takes the precaution of mounting media with the noexec option, which prevents direct execution of files (including autorun files). It does work with manually mounted media. 

The third tab, Cameras, has a checkbox labeled 'Import digital photos when connected.' When checked (which is the default), GNOME will look for a directory named dcim on any newly mounted USB media. If found, it will run the specified command (the default is gthumb- import ).

2.8.1.3. Configuring default actions in KDE

To configure the behavior of KDE when storage devices are inserted, open the KDE Control Center and select the configuration category Peripherals>Storage Media. The window shown in Figure 2-33 will appear.

Figure 2-33. KDE Removable Media configuration

Select Unmounted Removable Medium in the 'Medium types' menu. Two actions will be displayed: 'Open in New Window,' which mounts the drive and opens a Konqueror browse window, and Do Nothing, which causes a drive icon to be displayed on the desktop, which, when clicked, will mount and browse the drive.

To set one of these actions as the default, click on it, then click 'Toggle as Auto Action,' and then Apply. The selected action will take place automatically when new media is detected.

2.8.2. How Does It Work?

When a USB storage device is detected by the USB drivers, the hal subsystem takes note and sends a message on the dbus , a messaging system for desktop applications. GNOME or KDE desktop applications listen for messages on the dbus and then perform the action you have configured, such as mounting the drive or displaying the drive contents in a window.

USB devices use a set of data items called descriptors to inform the controlling host of their capabilities. The Class descriptor is used to identify storage devices. These devices, which understand the same commands used to control SCSI disk drives, are given a device name in the form /dev/sd<x> where <x> is a sequential drive letter ( sd stands for SCSI disk ). Partitions within a USB storage device, if present, are given device names in the form /dev/sd<xp> where <p> is the partition number (1 is the first partition).

When a drive is mounted in a Fedora system, a record of the mount is made in /etc/mtab , which can be viewed with the mount command:

$ mount
/dev/mapper/main-root on / type ext3 (rw)
/dev/proc on /proc type proc (rw)
/dev/sys on /sys type sysfs (rw)
/dev/devpts on /dev/pts type devpts (rw,gid=5,mode=620)
/dev/md0 on /boot type ext3 (rw)
/dev/shm on /dev/shm type tmpfs (rw)
/dev/mapper/main-home on /home type ext3 (rw)
/dev/mapper/main-var on /var type ext3 (rw,acl)
/dev/sda on /media/spreadsheet type ext2 (rw,noexec,nosuid,nodev)
/dev/sdb on /media/disk type vfat (rw,noexec,nosuid,nodev,shortname=winnt,uid=500)

This particular single USB storage device appears as two separate devices, highlighted in bold in this example: a disk drive, mounted using the filesystem label as the mount point ( /media/<fslabel> ), and a floppy disk (mounted as /media/disk in the output above). This is a common configuration used on older USB keys; the emulated floppy disk device is intended to store encryption or password software for accessing the main storage device. Removable media is mounted under the /media directory.

A more useful way of looking at the /etc/mtab table is to use df :

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/main-root
30G 8.9G 20G 32% /
/dev/md0 251M 33M 205M 14% /boot
/dev/shm 506M 0 506M 0% /dev/shm
/dev/mapper/main-home
31G 5.9G 25G 20% /home
/dev/mapper/main-var 36G 26G 9.3G 74% /var
/dev/sda 120M 1.6M 112M 2% /media/spreadsheet
/dev/sdb 1.4M 70K 1.4M 5% /media/disk