Why does nfsroot result in nonzero root user euid?

[David Wuertele <dave-gnus at bfnet dot com>]

OK, this bonehead question is off-topic, but I figure everyone here
has the understanding of libc and nfsroots that I lack:

When I run my target system mounting / off of an NFS export, I see
this:

  # whoami
  root
  # echo $UID
  0
  # echo $EUID
  0
  # strace -e trace=geteuid mount -n --bind /tmp/dir1 /tmp/dir2
  geteuid()                               = 500
  mount: must be superuser to use mount

500 happens to be the user id of the file owner on the NFS server.
The NFS server /etc/exports file says:

  /nfsroot *(rw,all_squash,anonuid=500,anongid=501)

But just because the server uses these user ids, I still don't see why
the client has to know anything about them.

If there's a better place to ask this, please let me know.
Thanks!


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