Detecting mounted drives on Linux and Mac OS X

Question 1

As far as the filesystem is concerned, there is no concept of drives in Unix/Linux (I can't vouch for MacOSX but I'd say it's the same). The closest thing would probably be mount points, but a normal application shouldn't bother about them since all is already available under the filesystem root / (hence the behaviour of QDir::drives() that you observe).

If you really want to see which mount points are in use, you could parse the output of the mount command (without any arguments) or, at least on Linux, the contents of the /etc/mtab file. Beware though, mount points can get pretty hairy real quick (loop devices, FUSE filesystems, network shares, ...) so, again, I wouldn't recommend making use of them unless your application is designed to administer them.

Keep in mind that on Unix-y OSes, mount points are normally a matter for system administrators, not end-users, unless we're speaking of removable media or transient network shares.

Edit: Following your clarifications in the comments, on Linux you should use getmntent or getmntent_r to parse the contents of the /etc/mtab file and thus get a list of all mount points and the corresponding devices.

The trick after that is to determine which ones you want to display (removable? network share?). I know that /sys/block/... can help with that, but I don't know all the details so you'll have to dig a bit more.

For example, to check whether /dev/sdd1 (a USB key) mounted on /media/usb0/ is a removable device, you could do (note how I use the device name sdd, not the partition name sdd1):

$ cat /sys/block/sdd/removable
1

As opposed to my main hard drive:

$ cat /sys/block/sda/removable
0

Hope this puts you on the right track.

Question 2

For OS X, the Disk Arbitration framework can be used to list and monitor drives and mount points

Question 3

Scraping the output of mount shell command is certainly one option on either platform - although, what is your definition of a drive here? Physical media, removable drivers, network volumes? You'll need to do a lot of filtering.

On MacOSX, the mount point for removable media, network volumes, and secondary hard-drives is always under /Volumes/, so simply enumerating items in this directory will do the trick if your definition of a drive is broad. This ought to be fairly safe as they're all automounted .

On Linux, there are a variety of locations depending on the particular distro in use. /mnt/ is the traditional, but there are others.

Question 4

In linux, the way to get information about drives currently mounted is to parse the mtab file. glibc provides a macro _PATH_MNTTAB to locate this file. See http://www.gnu.org/software/libc/manual/html_node/Mount-Information.html#Mount-Information

Question 5

If you know the format of the drive/drives in question, you can use the df command to output the list of drives from the console or programatically as a system command. For example, to find all the ext4 drives:

df -t ext4

You can simply add additional formats onto the same command if you are interested in more than one type:

df -t ext4 -t tmpfs

This is going to return to you the physical location of the drive, the amount of memory it has, the amount of memory used, the amount of memory free, the use% and where it is mounted on the filesystem.

df will show you all of the drives mounted on the system, but some are going to be things that aren't really what you are looking for like temporary file systems, etc.

Not sure if this will work on OSX or not, but it does work on my Ubuntu 12.04 distribution.

Question 6

Another way is to check for "Volumes"

df -H | grep "/Volumes"

Question 7

I know that this is old, but it failed to mention getfsstat which I ended up using in macos. You can get a list of mounts (which will include most disks) using getfsstat. See man 2 getfsstat for further information.