Fix file handles
Leaving file handles open is generally bad, and specifically worse for NFS mounts:
Cleanup mirror: full.
unlink .temp/dists/xenial-updates/universe/dep11/.nfs00000000002446110003c731: Device or resource busy at /usr/bin/debmirror line 2705.
WARNING: releasing 1 pending lock...
This is a "file deletion race" on NFS caused by multiple open handles to a given file. For each such file, the NFS client creates a "placeholder" to mark the thing that will be deleted once all open handles are closed. During cleanup,
debmirror attempts to delete the placeholders (among other things) which causes an error similar to that shown above.
There's also a fix for when
size is undefined.