How do I mount my FileVault 2-encrypted volume?

I have a Lion 10.7.2 system (on MacBook Air 13" 2011) which doesn't boot anymore after a restart. My HD is encrypted with FileVault 2, and after I click on my username and enter my password, it appears to be logging in but the apple logo turns into sort of a "forbidden" traffic sign, and stops there forever.

So I booted into Lion Recovery to try and repair permissions, but Disk Utility won't mount my Macintosh HD. It doesn't even allow me the option to mount or verify, they're greyed out.

An output from diskutil list recognizes my partition (/dev/disk0s2) as having the type Apple_CoreStorage.

Any way to make my encrypted partition mount?

You should be able to unlock or decrypt your FileVault 2-encrypted HD with Disk Utility. I've got a post on how to do this:

Using Disk Utility to unlock or decrypt your FileVault 2-encrypted boot drive:

http://derflounder.wordpress.com/2011/11/23/using-disk-utility-to-unlock-or-decrypt-your-filevault-2-encrypted-boot-drive/

If unlocking via Disk Utility isn't working, you may need to use your recovery key. I've got another post on how you can unlock using your recovery key using the command line:

Unlock or decrypt your FileVault 2-encrypted boot drive from the command line:

http://derflounder.wordpress.com/2011/11/23/using-the-command-line-to-unlock-or-decrypt-your-filevault-2-encrypted-boot-drive/

You could try to repair the disk through termainal

e.g. where disk0 will be the partition you want to repair

  diskutil repairVolume /dev/disk0

if you just type in

diskutil

This will give you a list of options e.g. mounting the drive etc.

Will probably not help but worth a try.

I was having the same issue with 10.7.4 just now and this question and the comments helped but nothing really worked. But I did try using diskutil from the command line and I got it to work. df showed me my mount points of slash:

{dhcp} df
Filesystem    1024-blocks      Used    Avail Capacity  Mounted on
/dev/disk1      243966468 206648460 37062008    85%    /

I used diskutil list to show me my partitions:

{dhcp} diskutil list
    /dev/disk0
      ...
   /dev/disk1
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:                  Apple_HFS SSD Hard DIsk          *249.8 GB   disk1

Then I was able to do the repair permissions from the command line on /dev/disk1:

{dhcp} diskutil repairPermissions /dev/disk1
Started verify/repair permissions on disk1 SSD Hard DIsk
Group differs on "Library/Java"; should be 0; group is 80
Permissions differ on "Library/Java"; should be drwxr-xr-x ; they are drwxrwxr-x 
...

I was also able to verify the volume:

{dhcp} diskutil verifyVolume /dev/disk1 
Started file system verification on disk1 SSD Hard DIsk
Checking storage system
Checking volume
...