how big does /tmp need to be?

[Bob Smith]

> > The only reason I can think of to use a separate partition for anything,
> > be it /var or /home, is to preserve that data when something else is
> > being destroyed/overwritten.

Or to make sure it does get destroyed/overwritten, see below.

> People create partitions for other reasons too.
> 
> One is some kind of performance/disk size issues - e.g. /tmp is on a
> separate faster drive, or it's local when all your other partitions
> are NFS mounted.

Well, I want /tmp to be on an encrypted filesystem using the
crypttab "tmp" option. I think this means the partition will be
reinitialized at boot-up with a random key and an ext2 will be
created from scratch on it.  (I have a spare 10GB partition I can
use for this.)

There's nothing in /tmp that needs to persist between boots, is
there?