Mergemaster won't run on NFS mount

I have been updating FreeBSD for years on my fastest computer and then
NFS mounting /usr/src and /usr/obj to share with other PC's.  I just
updated FreeBSD-CURRENT to 326070 and was able to install the kernel and
world.  When I attempted to run mergemaster, I received the following
error message:

*** Creating the temporary root environment in /var/tmp/temproot
 *** /var/tmp/temproot ready for use
 *** Creating and populating directory structure in /var/tmp/temproot

/bin/sh: cannot create freebsd.cf: Permission denied

  *** FATAL ERROR: Cannot 'cd' to /usr/src and install files to
      the temproot environment

In the many years that I have been doing updates using NFS shares, it
has never required write access to /usr/src to use for a temproot.

Tom


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