Regain lost space hidden in trash on external disks

Think you emptied the trash on your external drive? Even if you did, there may be large amounts of trash still lurking on external or network drives that has not been emptied. As most folks know, the trash is segregated by user ID, and when you empty the trash, it only empties your user's trash -- even on FireWire disks. 

If you delete a user's account on your computer, the system won't remove the trash for that user ID on the external or network drive. This can also happen if you have ever shared a disk between two computers. Since the UIDs on one computer may not be the same as the other, trashes can be created by one computer that cannot be emptied by the other. This can even happen if your username is the same on both computers, but your UIDs (e.g. 501 an 502) are different. 

Thus periodically one needs to manually remove the trash like this, in Terminal: 

Quote:

$ sudo -s
$ rm -rf /Volumes/"my_external_disk"/.Trashes/*
$ exit

Replace "my_external_disk" is the name of the disk from which you want to remove all trash from all users. (The quotes are used in case of spaces in the disk name.) I noticed this because I had lost about one-third of my disk space to this phenomena, even though I only had one user account on my present computer.