LinuxQuestions.org - NFS server apparently stops

I posted this yesterday, but it seems to have disappeared. If you feel it belongs in another forum, please let me know.

I'm teaching an online embedded Linux class for UC San Diego extension. Two of my students seem to be having the same problem that I've never seen before. Both are running F17 under VMWare.

They can't mount the target board's root file system over NFS. Executing service nfs-server status yields:

[root@localhost linux-3.5.3]# service nfs-server status
Redirecting to /bin/systemctl status nfs-server.service
nfs-server.service - NFS Server
Loaded: loaded (/usr/lib/systemd/system/nfs-server.service; enabled)
Active: active (exited) since Sat, 19 Oct 2013 14:59:27 -0600; 7s ago
Process: 2090 ExecStartPost=/usr/lib/nfs-utils/scripts/nfs-server.postconfig (code=exited, status=0/SUCCESS)
Process: 2088 ExecStartPost=/usr/sbin/rpc.idmapd $RPCIDMAPDARGS (code=exited, status=0/SUCCESS)
Process: 2086 ExecStartPost=/usr/sbin/rpc.mountd $RPCMOUNTDOPTS (code=exited, status=0/SUCCESS)
Process: 2074 ExecStart=/usr/sbin/rpc.nfsd $RPCNFSDARGS ${RPCNFSDCOUNT} (code=exited, status=0/SUCCESS)
Process: 2073 ExecStartPre=/usr/sbin/exportfs -r (code=exited, status=0/SUCCESS)
Process: 2071 ExecStartPre=/usr/sbin/rpc.rquotad $RPCRQUOTADOPTS (code=exited, status=0/SUCCESS)
Process: 2068 ExecStartPre=/usr/lib/nfs-utils/scripts/nfs-server.preconfig (code=exited, status=0/SUCCESS)
Main PID: 2072 (rpc.rquotad)
CGroup: name=systemd:/system/nfs-server.service
├ 2072 /usr/sbin/rpc.rquotad
├ 2087 /usr/sbin/rpc.mountd
└ 2089 /usr/sbin/rpc.idmapd

Oct 19 14:59:26 localhost.localdomain rpc.mountd[2087]: Version 1.2.5 starting

where the key word is exited. On my system, which is F17 running under VirtualBox, it says running. Looking at the graphical services dialog, on my system nfs-server shows as running, while on theirs it shows as "finished". In all three cases the firewall is disabled.

What's going on? Thanks.