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From: David Empson on 9 Mar 2010 18:13
Stephen2 <Stephen(a)mailinator.com> wrote:

> Does anyone know what this folder is for. I'm guessing it's a work
> area applications use for temporary storage or something.

Yes. I don't fully understand it, but it appears that the system
automatically creates a randomly named folder in /private/var/folders
for each user account for use as temporary storage. I first noticed this
mechanism in Leopard, but it may have been there earlier.

The randomly named folder is in a parent folder which has a name that
has the same first two letters, e.g.

/private/var/folders/mp/mpAQxZfAFAtaBRSM1LtlbY+++WX

The +++ near the end appears to be consistent.

Inside the randomly named folder are typically four subfolders:
-Caches-, -Tmp-, CleanupAtStartup and TemporaryItems.

Some of these obviously date back to Mac OS 9, which had hidden
CleanupAtStartup and TemporaryItems folders at the top level of the hard
drive. That mechanism had to be modified to cope with multiple users,
each of which might need to create files of the same name in
TemporaryItems (for example).

I'm guessing that the random folder name is an encoded version of the
128-bit UUID (universally unique identifier) which is associated with
each user account, therefore the random folder name is fixed at the time
the user account is created.

These folders appear to exist long term, and some of the files inside
them are never deleted automatically, while others are.

My account's randomly named folder is using about 134 MB.

There is also a /private/var/folders/zz/ which contains several
similarly named temporary folders used by various system-level accounts
(all starting with zz).

> Is it safe to delete any of these folders?

I wouldn't try this with my own one until I'd experimented with a
sacrificial account.

I expect the system will recreate them automatically.

It would be a good idea not to try deleting them while logged in as the
user corresonding to that folder - log in as a different user, then use
'su' to temporarily change to the user owning the folder you want to
delete.

(This is less risky than using 'sudo rm' to delete files, which has
unrestricted access to anything on the computer, and a typing error
could have disastrous consequences.)

> I mean, I did delete one of the folders to fix a problem with superduper
> and everything seems to be ok so far. I basically screwed up permissions
> on my home folder somehow at the weekend when I was dabbling. This
> resulted in a problem with superduper so that whenever I changed anything
> in the settings the application wouldn't quit. The console log showed a
> permissions error deleting a file in a subfolder of
> /private/var/folders/f6.


--
David Empson
dempson(a)actrix.gen.nz
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