XQuartz disk image won't open Every time I try to open the .dmg to install XQuartz, a window pops up saying the following disk images couldn't be opened and the reason shown is not recognized. I don't know if I need another application to open it or if the file is corrupted, or if it's some other problem entirely.
I'd say the file downloaded is corrupted, you should be able to open the .dmg by simply double clicking it (I downloaded XQuartz a couple of days ago and could open the .dmg without a problem).

Unfortunately, the download page doesn't provide a checksum to check against, so I'll provide the one I generated:


  98b2ca8580046d5b91250c5a244c8182437dc9d7


This checksum uniquely identifies the XQuarz .dmg.

You can generate a checksum of XQuartz on your Mac like this (from http://support.apple.com/kb/HT1652):


Open Terminal (in /Application/Utilities)
Type:

openssl sha1 ~/Downloads/XQuartz-2.7.4.dmg 

(adapt to the path where XQuartz-2.7.4.dmg was downloaded)
Compare the number you get with the number above. If they are different, the file is corrupted.