How to fix mounting problem with external drive? I have a USB external hard drive with AC adapter that works fine with an Ubuntu machine. But when I plug it into my MacBook Air it lists one partition on the finder, and does not mount the other.

Even though it is listed on the finder, it shows that there are no files on the drive (even though there are).

Tried both USB ports with the same result.

Disk Utility does not see it.

How to fix?

OSX 10.7.5
The answer to your questions is in the "Disk Utilities" application: just type this in the search box on the top-right corner of your screen, and launch the application.

For every device connected, you will see much information. Relevant to analyse your problem is the "format" information: HDFS, Mac OS Extended, ExFAT, FAT32, ext3, ext4...

I guess because your harddisk comes from Ubuntu, it must be ext3 or ext4. If that is the case, please read the following answer for further help: https://apple.stackexchange.com/a/29914/44080