missing 20gb on hard drive

What do you see in ->About This Mac->[More Infor...]->[Storage]

Try using the linked program to see what is taking up your disk space.

OmniDiskSweeper

They also might be local snapshots if you are using a laptop.

Local Snapshots - About

Local Snapshots on Portable Macs

Looks like you only have 20g free (Not sure why your Finder Info shows more).

One final place to look is with df in Terminal:

df -Hl

I get:

Filesystem Size Used Avail Capacity iused ifree %iused Mounted on

/dev/disk0s2 120G 75G 46G 63% 18302149 11110219 62% /

And my Finder (with ⌘/) shows: 45.51 GB available, and ⌘I on Macintosh HD also reports Available 45.51 GB

I think your 20 GB are being used by OS X as swap space.

Restart the Mac and try all those disk space methods/apps immediately. Any difference?

.

Robin Bonathan wrote:

mobilebackups is showing 124gb used.

In Terminal:

sudo tmutil disablelocal

Try that, and if you want to re-enable local snapshots:

sudo tmutil enablelocal

From man tmutil:

disablelocal

Turn off local Time Machine snapshots and trigger automatic

cleanup of accumulated local snapshot data. Requires root privi-

leges.

You may notice a difference in available space statistics between Disk Utility, Finder, and Get Info inspectors. This is expected and can be safely ignored. The Finder displays the available space on the disk without accounting for the local snapshots, because local snapshots will surrender their disk space if needed.

About Time Machine's "local snapshots" on portable Macs

As Eric suggested, it looks like it may be Local Snapshots

Try resetting with sudo tmutil disablelocal (see my previous reply)

(FWIW, I have a MacBook Air, backup to a network drive with Time Machine, and I keep local snapshots disabled)