The ebuild and emerge commands apparently use various temporary files, which are created in the /tmp directory. Could these programs please erase the files when they terminate? That would help not to clutter the /tmp directory up any more than it is already. :-)
Azarah, could you look into this? In particular, it seems that /tmp/sandboxpids.tmp filling up is causing the sandbox to die even with Portage 2.0.26. I am not sure when it's OK to clean this file so I'm assigning this bug to you.
*** Bug 6707 has been marked as a duplicate of this bug. ***
I recently encountered this same problem with /tmp/sandboxpids.tmp (I believe that's the correct name). It existed for some time, I'm unsure how long, and apparently was interfering with Portage. Emerge'ing anything would stall at "Emerging {package-name} to /" indefinately. Removing the file seems to have cured it. In the process, however, I attempted to untar the Portage rescue tarball, per the instructions in README.RESCUE, but it crashed when trying to emerge portage. Apparently the problem was the /var/cache/edb/counter file. When moved out of that directory the problem(s) went away immediately.
Should be fixed now in latest portage, as sandbox now removes /tmp/sandboxpids.tmp
